ISO/FDIS 4925

Road vehicles — Specification of non-petroleum-based brake fluids for hydraulic systems

This document provides the specifications, requirements and test methods, for non-petroleum-based fluids used in road-vehicle hydraulic brake and clutch systems that are designed for use with such fluids and equipped with seals, cups or double-lipped type gland seals made of styrene-butadiene rubber (SBR) and ethylene-propylene elastomer (EPDM).

Véhicules routiers — Spécifications pour liquides de frein à base non pétrolière pour systèmes hydrauliques

General Information

• Status: Not Published
• ICS: 43.040.40 - Braking systems
• ICS: 75.120 - Hydraulic fluids
• Technical Committee: ISO/TC 22/SC 33 - Vehicle dynamics and chassis components
• Drafting Committee: ISO/TC 22/SC 33/WG 14 - Brake fluids
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 09-Mar-2026
• Completion Date: 09-Mar-2026

Relations

• Revises: ISO 4925:2020 - Road vehicles — Specification of non-petroleum-based brake fluids for hydraulic systems
• Effective Date: 18-Nov-2023

Overview

ISO/FDIS 4925 sets out the international requirements for non-petroleum-based brake fluids designed for hydraulic systems in road vehicles. Developed by the International Organization for Standardization (ISO), this standard is intended for manufacturers, suppliers, and testing laboratories involved in the formulation and assessment of hydraulic brake and clutch fluids. The document covers essential specifications, test methods, and quality criteria necessary to ensure the safety and performance of brake fluids compatible with components made from styrene-butadiene rubber (SBR) and ethylene-propylene diene monomer (EPDM) elastomers.

Key Topics

• Scope and Purpose: Specifies performance requirements and testing methods for non-petroleum-based brake fluids used in road-vehicle hydraulic braking and clutch systems.
• Compatibility: Ensures fluids work with systems equipped with SBR and EPDM rubber seals, cups, or gland seals.
• Quality Control: Emphasizes materials' clarity, absence of suspended matter, and prevention of sediment or contamination.
• Performance Requirements:
  • Viscosity: Evaluated at low and high temperatures for reliable operation in varying climates.
  • Equilibrium Reflux Boiling Point (ERBP): Assessing boiling and wet boiling points prevents brake failure due to vapor lock.
  • pH Levels: Ensures chemical stability and prevents corrosion or degradation of system components.
  • Corrosion Resistance: Mandates strict limits on metal corrosion to safeguard brake system integrity.
  • Effect on Rubber: Examines the compatibility and durability of rubber components in contact with brake fluid.
  • Stability: Requires high temperature and chemical stability for safe, extended use.
  • Wear and Noise: Includes pass/fail testing for friction-induced noise and wear to address evolving industry concerns.
  • Water Tolerance and Miscibility: Specifies behavior in the presence of water and compatibility with reference fluids.

Applications

ISO/FDIS 4925 is applied primarily in the following areas:

• Brake Fluid Manufacturing: Guides the formulation, development, and quality control of non-petroleum-based (e.g., glycol-based) brake and clutch fluids.
• Automotive OEMs and Component Suppliers: Supports the design and validation of vehicle hydraulic systems that utilize SBR or EPDM rubber components.
• Testing Laboratories: Informs rigorous, standardized test methods for viscosity, boiling point, compatibility, corrosion, and more.
• Regulatory Compliance: Serves as a reference point for national regulations concerning vehicle safety, performance, and environmental impact.
• Brake System Maintenance: Provides service guidelines and safety assurance for mechanics and automotive service providers when selecting fluids for vehicles with specified rubber component compatibility.

Related Standards

• ISO 4926: Reference fluids for non-petroleum-based hydraulic braking systems, defining base fluids for compatibility and performance testing.
• ASTM D 1120 / D 1121 / D 3185: US standards for defining properties such as boiling point and rubber compatibility.
• DIN 51834-5: Test methods for evaluating friction-induced noise in brake fluids in EPDM-metal contacts.
• ISO 37 / ISO 48-2 / ISO 812: Methods for measuring the physical and mechanical properties of vulcanized rubbers, relevant for elastomeric component assessment.

Practical Value

ISO/FDIS 4925 enhances road safety by ensuring brake fluids meet global standards for chemical and mechanical performance. Its rigorous test protocols help manufacturers avoid premature system failures caused by fluid breakdown, corrosion, or incompatibility with key elastomeric parts. The standard streamlines compliance, aids in global market access, and fosters the production of reliable, high-performance non-petroleum-based hydraulic brake fluids for modern vehicles. For regulators and industry professionals, it provides a credible reference for certification, inspection, and continuous improvement of automotive safety products.

Standards Content (Sample)

DRAFT
International
Standard
ISO/DIS 4925
ISO/TC 22/SC 33
Road vehicles — Specification of
Secretariat: DIN
non-petroleum-based brake fluids
Voting begins on:
for hydraulic systems
2025-09-04
Véhicules routiers — Spécifications pour liquides de frein à base
Voting terminates on:
non pétrolière pour systèmes hydrauliques
2025-11-27
ICS: 43.040.40; 75.120
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
This document has not been edited by the ISO Central Secretariat.
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 4925:2025(en)
DRAFT
ISO/DIS 4925:2025(en)
International
Standard
ISO/DIS 4925
ISO/TC 22/SC 33
Road vehicles — Specification of
Secretariat: DIN
non-petroleum-based brake fluids
Voting begins on:
for hydraulic systems
Véhicules routiers — Spécifications pour liquides de frein à base
Voting terminates on:
non pétrolière pour systèmes hydrauliques
ICS: 43.040.40; 75.120
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
This document has not been edited by the ISO Central Secretariat. BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: [phone]
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 4925:2025(en)
ii
ISO/DIS 4925:2025(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Materials . 2
5 Specifications . 2
6 Test methods . 4
6.1 Viscosity .4
6.1.1 General .4
6.1.2 Repeatability (single analyst) .4
6.1.3 Reproducibility (multi-laboratory) .4
6.2 Equilibrium reflux boiling point (ERBP) .5
6.2.1 General .5
6.2.2 Preparation of apparatus .5
6.2.3 Test procedure.5
6.2.4 Repeatability (single analyst) .5
6.2.5 Reproducibility (multi-laboratory) .5
6.2.6 Wet ERBP test .6
6.3 pH .9
6.4 Fluid stability .9
6.4.1 High-temperature stability .9
6.4.2 Chemical stability .10
6.5 Corrosion .10
6.5.1 Metal strip characteristics prior to testing .10
6.5.2 Preparation of joints .10
6.5.3 Test procedure.11
6.6 Fluidity and appearance at low temperatures .11
6.6.1 At −40 °C for 144 h .11
6.6.2 At −50 °C for 6 h .11
6.7 Water tolerance .11
6.7.1 At −40 °C for 22 h .11
6.7.2 At 60 °C for 22 h. 12
6.8 Compatibility/miscibility with ISO 4926 fluid . 12
6.8.1 At −40 °C for 22 h . 12
6.8.2 At 60 °C for 22 h. 12
6.9 Resistance to oxidation . 12
6.10 Effect on rubber . 13
6.10.1 Test procedures . 13
6.10.2 Repeatability (single analyst) . 13
6.10.3 Reproducibility (multi-laboratory) .14
6.11 Reserve alkalinity according to ASTM D 1121 .14
6.12 Resistance to friction induced noise .14
6.13 Resistance to friction induced wear .14
Annex A (normative) ISO styrene-butadiene rubber (SBR) brake cups for testing brake fluid .15
Annex B (normative) Corrosion test strips.18
Annex C (informative) Corrosion strip assembly . 19
Annex D (normative) Standard ethylene, propylene and diene (EPDM) terpolymer rubber
slabstock .20
Annex E (normative) Triethylene glycol monomethyl ether (TEGME) brake fluid grade.22

iii
ISO/DIS 4925:2025(en)
Annex F (normative) Wear test in the translatory oscillation tribometer to quantify the
friction-induced wear of a brake fluid in EPDM-metal contact .25
Bibliography .29

iv
ISO/DIS 4925:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee 33, Chassis
systems and components.
This fourth edition cancels and replaces the third edition (ISO 4925:2005), (2020 instead of 2005)which has
been technically revised.
The main changes compared to the previous edition are as follows:
— the note of intended introduction of a wear and noise test currently under development in the SAE and
ISO TF lubrication is replaced by introduction of these developed tests methods:
— lubrication requirement for noise test is added as pass/fail criterion 6.12;
— lubrication requirement for wear test is added as pass/fail criterion 6.13;
— few editorial changes.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
ISO/DIS 4925:2025(en)
Introduction
The specifications for fluids given in this document incorporate a range of performance standards in use
throughout the world at the time of publication. To the already existing requirements to further lubrication
requirements are added for all classes 3, 4, 5-1, 6 and 7 .
The major use of these fluids is in the hydraulic brake and clutch systems of road vehicles, but they can also
be used in any suitable hydraulic system.

vi
DRAFT International Standard ISO/DIS 4925:2025(en)
Road vehicles — Specification of non-petroleum-based brake
fluids for hydraulic systems
1 Scope
This document provides the specifications, requirements and test methods, for non-petroleum-based fluids
used in road-vehicle hydraulic brake and clutch systems that are designed for use with such fluids and
equipped with seals, cups or double-lipped type gland seals made of styrene-butadiene rubber (SBR) and
ethylene-propylene elastomer (EPDM).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ASTM D 3185:2006, Standard test methods for rubber—Evaluation of SBR (Styrene-Butadiene Rubber)
including mixtures with oil
ASTM D 91, Standard test method for precipitation number of lubricating oils
ASTM D 395, Standard test methods for rubber property — Compression set
ASTM D 412, Standard test methods for vulcanized rubber and thermoplastic elastomers — Tension
ASTM D 746, Standard test method for brittleness temperature of plastics and elastomers by impact
ASTM D 865, Standard test method for rubber — Deterioration by heating in air (test tube enclosure)
ASTM D 1120, Standard test method for boiling point of engine coolants
ASTM D 1121, Standard test method for reserve alkalinity of engine coolants and antirusts
ASTM D 1123, Standard test methods for water in engine coolant concentrate by the Karl Fisher reagent method
ASTM D 1415, Standard test method for rubber property — International hardness
ASTM D 3182, Standard practice for rubber — Materials, equipment and procedures for mixing standard
compounds and preparing standard vulcanized sheets
ASTM E 298, Standard test methods for assay of organic peroxides
DIN 51834-5, Testing of lubricants - Tribological test in the translatory oscillation apparatus - Part 5:
Quantification of the friction-induced noise development of brake fluids in EPDM-metal contacts
ISO 37, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties
ISO 48-2, Rubber, vulcanized or thermoplastic — Determination of hardness (hardness between 10 IRHD and
100 IRHD)
ISO 812, Rubber, vulcanized or thermoplastic — Determination of low-temperature brittleness
ISO 815 (all parts), Rubber, vulcanized or thermoplastic — Determination of compression set
ISO 3104, Petroleum products — Transparent and opaque liquids — Determination of kinematic viscosity and
calculation of dynamic viscosity

ISO/DIS 4925:2025(en)
ISO 4926, Road vehicle — Hydraulic braking systems — Non petroleum base reference fluids
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Materials
On visual inspection, the fluid shall be clear and free of suspended matter, dirt and sediment. The quality of
the materials used shall be such that the resulting product conforms to the requirements of this document
and that uniformity of performance is ensured. Fluids may be dyed, provided no confusion is possible
between them and other types of fluids.
5 Specifications
The product shall meet the requirements for the appropriate class in accordance with Table 1, using the test
methods according to Clause 6.
Table 1 — Brake fluid specifications — Tests and requirements
Requirement(s)
Test
method Test description Unit
Class Class Class Class Class
(subclause)
3 4 5–1 6 7
6.1 Viscosity
at −40 °C mm /s ≤1 500 ≤900 ≤750 ≤750
at 100 °C mm /s ≥1,5
6.2 Equilibrium reflux boiling point (ERBP) °C ≥205 ≥230 ≥260 ≥250 ≥260
6.2.6 Wet ERBP °C ≥140 ≥155 ≥180 ≥165 ≥180
6.3 pH — 7 to 11,5
6.4 Fluid stability
6.4.1 High-temperature stability °C ±5 °C
6.4.2 Chemical stability °C ±5 °C
6.5 Corrosion
Metal strip characteristics after testing
Mass change
Tinned iron mg/cm −0,2 to 0,2
Steel mg/cm −0,2 to 0,2
Aluminium mg/cm −0,1 to 0,1
Cast iron mg/cm −0,2 to 0,2
Brass mg/cm −0,4 to 0,4
Copper mg/cm −0,4 to 0,4
Aspect — No pitting or roughness outside
contact area
Staining/discoloration — Permitted
Liquid characteristics after testing

ISO/DIS 4925:2025(en)
TTaabblle 1 e 1 ((ccoonnttiinnueuedd))
Requirement(s)
Test
method Test description Unit
Class Class Class Class Class
(subclause)
3 4 5–1 6 7
Aspect — No gel, none adhering crystals
pH — 7 to 11,5
Sediment % vol. ≤0,1
Rubber cup characteristics after testing
Blisters or carbon black separation at — None
surface
Hardness decrease IRHD ≤15
Base diameter increase mm ≤1,4
Volume increase % ≤16
6.6 Fluidity and appearance at low temperatures
6.6.1 at −40 °C for 144 h
Aspect — Clear and homogeneous
Bubble flow time s ≤10
Sediments — Absence
6.6.2 at −50 °C for 6 h
Aspect — Clear and homogeneous
Bubble flow time s ≤35
Sediments — Absence
6.7 Water tolerance
6.7.1 at −40 °C for 22 h
Aspect — Clear and homogeneous
Bubble flow time s ≤10
Sediments — Absence
6.7.2 at 60 °C for 22 h
Aspect — Clear and homogeneous
Sediments % vol. ≤0,05
6.8 Compatibility/miscibility with ISO 4926 fluid
6.8.1 at − 40 °C for 22 h
Aspect — Clear and homogeneous
Sediments — Absence
6.8.2 at 60 °C for 22 h
Aspect — Clear and homogeneous
Sediments % vol. ≤0,05
6.9 Resistance to oxidation
Metal strip aspect No pitting or roughness
—
no more than a trace of gum
Staining/discoloration — Permitted
Mass change of aluminium strip mg/cm −0,05 to +0,05
Mass change of cast iron strip mg/cm −0,3 to +0,3
6.10 Effect on rubber
6.10.1.1 Styrene butadiene rubber (SBR)
at 120 °C
Cup diameter increase mm 0,15 to 1,4

ISO/DIS 4925:2025(en)
TTaabblle 1 e 1 ((ccoonnttiinnueuedd))
Requirement(s)
Test
method Test description Unit
Class Class Class Class Class
(subclause)
3 4 5–1 6 7
Hardness change IRHD −15 to 0
Volume increase % 1 to 16
Blisters or carbon black separation at None
—
surface
6.10.1.2 Ethylene propylene diene monomer (EPDM)
at 120 °C
Hardness change IRHD −15 to 0
Volume change % 0 to 10
Blisters or carbon black separation at None
—
surface
6.11 Reserve alkalinity according to ASTM D 1121 mL to be reported
6.12 FIN
1 .
6.13 FIW
.
6 Test methods
6.1 Viscosity
6.1.1 General
Determine the kinematic viscosity of the fluid in accordance with ISO 3104.
2 2
Report the viscosity to the nearest 1 mm /s at −40 °C and to the nearest 0,01 mm /s at +100 °C. Duplicate
runs that agree within 1,2 % relative are acceptable for averaging (95 % confidence level).
6.1.2 Repeatability (single analyst)
The coefficient of variation of results (each the average of duplicates) obtained by the same analyst on
different days shall not be greater than 0,4 % at 47 degrees of freedom. Two such values shall be considered
unacceptable (95 % confidence level) if they differ by more than 1,2 %.
6.1.3 Reproducibility (multi-laboratory)
The coefficient of variation of results (each the average of duplicates) obtained by analysts in different
laboratories shall not be greater than 1,0 % at 15 degrees of freedom. Two such values shall be considered
unacceptable (95 % confidence level) if they differ by more than 3,0 %.

ISO/DIS 4925:2025(en)
6.2 Equilibrium reflux boiling point (ERBP)
6.2.1 General
1)
Determine the ERBP of the fluid in accordance with ASTM D 1120 , but with the following changes to the
procedure and to the apparatus (see Figure 1 and Figure 2).
— Thermometer: immersion shall be 76 mm and the thermometer shall be calibrated.
— Heat source: use either a suitable variac-controlled heating mantle designed to fit the flask, or an electric
heater with rheostat heat control.
6.2.2 Preparation of apparatus
Thoroughly clean and dry all glassware before use. Attach the flask to the condenser. When using a heating
mantle, place the mantle under the flask and support it with a suitable ring clamp and laboratory-type
stand, holding the whole assembly in place by a clamp. When using a rheostat-controlled heater, centre a
standard porcelain or other suitable refractory having a diameter opening of 32 mm to 38 mm over the
heating element of the electric heater and mount the flask on the refractory so that direct heat is applied to
the flask only through the opening in the refractory. Place the whole assembly in an area free from draughts
or other causes of sudden temperature changes.
6.2.3 Test procedure
Turn on the condenser water and apply heat to the flask at such a rate that the fluid is refluxing within
(10 ± 2) min at a rate higher than one drop per second. The reflux rate shall not exceed five drops per second.
Immediately adjust the heat input to obtain a specified equilibrium reflux rate of one drop per second to two
drops per second over the next (5 ± 2) min period. Maintain a timed and constant equilibrium reflux rate
of one drop per second to two drops per second for an additional 2 min; record the average value of four
temperature readings taken at 30 s intervals at the equilibrium reflux boiling point.
Report the boiling point to the nearest degree Celsius. Duplicate results that agree within 3 °C are acceptable
for averages (95 % confidence level).
6.2.4 Repeatability (single analyst)
The standard deviation of results (each the average of duplicates), obtained by the same analyst on
different days shall not be greater than 1,3 °C at 34 degrees of freedom. Two such values shall be considered
unacceptable (95 % confidence level) if they differ by more than 4 °C.
6.2.5 Reproducibility (multi-laboratory)
The standard deviation of results (each the average of duplicates), obtained by analysts in different
laboratories, shall be not greater than 3,5 °C at 15 degrees of freedom. Two such values shall be considered
unacceptable (95 % confidence level) if they differ by more than 10,5 °C.
1) Boiling chips for use with ASTM D 1120 can be obtained from Electro Minerals Co. (US) Inc, PO Box 423, Niagara Falls,
NY 14302, USA, or from the Society of Automotive Engineers (SAE), 400 Commonwealth Drive, Warrendale Pa 15096,
USA (RM-75). Boiling chip is an example of a suitable product available commercially. This information is given for the
convenience of users of this document and does not constitute an endorsement by ISO of this product.

ISO/DIS 4925:2025(en)
6.2.6 Wet ERBP test
6.2.6.1 Apparatus
6.2.6.1.1 Two corrosion test jars or equivalent screw-top, straight-sided, round glass jars each having
a capacity of about 475 ml and approximate inner dimensions of 100 mm height by 75 mm diameter, with
2)
matching lids having new, clean inserts providing water-proof and vapour-proof seals .
6.2.6.1.2 Desiccator and cover: bowl-form glass desiccator with 250 mm inside diameter, having a
matching tubulated cover fitted with a No. eight rubber stopper (see Figure 3).
6.2.6.1.3 Desiccator plate of 230 mm diameter, perforated porcelain desiccator plate, without feet, glazed
3)
on one side (No.18 or equivalent) .
2) Suitable corrosion test jars (RM-49) and tinned steel lids (RM-63) can be obtained from the Society of Automotive
Engineers (SAE), 400 Commonwealth Drive, Warrendale, Pa 15096, USA.
3) Desiccator plates (No. 08-641C) can be obtained from Fischer Scientific, Springfield, New Jersey, USA or CeramTec
AG (No. 602786), Glaswerk Wertheim KG (No. 911743431) or equivalents, according to DIN/ISO 12911, diameter 235
mm. Corrosion test jars (RM-49), tinned steel lids (RM-63) and desiccator plates (No. 08-641C) are examples of suitable
products available commercially. This information is given for the convenience of users of this document and does not
constitute an endorsement by ISO of these products.

ISO/DIS 4925:2025(en)
Dimensions in millimetres
Key
1 water outlet
2 water jacket
3 thermometer
4 plastic screw cap or rubber sleeve
5 boiling chips
6 19/38 joint
7 water inlet
Figure 1 — Boiling point test apparatus

ISO/DIS 4925:2025(en)
Dimensions in millimetres
Key
1 19/38 joint
2 fire-polished
3 screw joint or rubber sleeve
a
Internal diameter: 8 to 9.
Figure 2 — Detail of 100 ml short-neck flask
6.2.6.2 Test procedure
To determine the wet ERBP of the fluid in duplicate (see Figure 3), first, humidify a 350 ml sample of the
fluid under controlled conditions, using 350 ml of triethylene glycol mono methyl ether (TEGME), follow
Annex E, to establish the end point for humidification.
Lubricate the ground-glass joint of the desiccator.
Then, pour (450 ± 10) ml of distilled water into the desiccator and insert the perforated porcelain plate.
Immediately place one open corrosion test jar containing (350 ± 5) ml of the humidified test fluid into
the desiccator. Place a second open corrosion test jar containing (350 ± 5) ml of TEGME control fluid
into the same desiccator. The water content of the TEGME control fluid at the start of exposure shall be
(0,50 ± 0,05) % by weight.
Next, replace the desiccator cover and place immediately in a forced ventilation oven set at (50 ± 1) °C.
Periodically, during oven humidification, remove the rubber stopper from the desiccator and, using a long-
needle hypodermic syringe, quickly sample the control fluid and determine its water content in accordance
with ASTM D 1123. A maximum of 10 ml of fluid shall be removed in total. When the water content of the
control fluid has reached (3,70 ± 0,05) % by weight, remove the desiccator from the oven and seal the test jar
promptly using a screw-cap jar lid. Allow the sealed jar to cool for 60 min to 90 min at (23 ± 5) °C. Determine
the ERBP in accordance with 6.2.1 and 6.2.3.

ISO/DIS 4925:2025(en)
Dimensions in millimetres
Key
1 rubber stopper
2 glass desiccator with tubulated cover
3 lubricated ground joint
4 TEGME (see Annex E)
5 corrosion test jars
6 fluid sample
7 porcelain desiccator plate
8 water
Figure 3 — Humidification apparatus
6.3 pH
Mix the fluid with an equal volume of a mixture 50 % ethanol and 50 % distilled water neutralized to a pH
of 7,0 ± 0,1. Determine the pH of the resulting solution electrometrically at (23 ± 5) °C, using a pH meter
equipped with a calibrated full range (0 to 14) glass electrode and a calomel reference electrode, as specified
in ASTM D 664.
Clouding or muddiness of the resulting solution is permitted in the determination.
6.4 Fluid stability
6.4.1 High-temperature stability
To determine the high-temperature stability of the fluid, heat a fresh sample of the original test fluid to a
temperature of (185 ± 2) °C according to the procedure specified in 6.2.3 and maintain it at that temperature
for (120 ± 5) min before determining the boiling point of the fluid, also in accordance with 6.2.3. The
difference between this observed boiling point and that previously determined using that test procedure
shall be considered as the change in boiling point of the fluid.

ISO/DIS 4925:2025(en)
6.4.2 Chemical stability
To determine the chemical stability of the fluid, first, mix 30 ml of the fluid with 30 ml of the fluid specified
in ISO 4926. Determine the ERBP of this fluid mixture by use of the test apparatus specified in 6.2, applying
heat to the flask at such a rate that the fluid refluxes within (10 ± 2) min at a rate of between one drop per
second and five drops per second.
Record the maximum fluid temperature observed during the first minute after the fluid begins refluxing
at a rate higher than one drop per second. Over the next (15 ± 1) min, adjust and maintain the rate of reflux
to one drop per second to two drops per second. Maintain a timed and constant equilibrium reflux rate of
from one drop per second to two drops per second for an additional 2 min, recording the average value of
four temperature readings at 30 s intervals as the final equilibrium reflux boiling point. Chemical reversion
is evidenced by the change in temperature between the maximum fluid temperature recorded and the final
equilibrium reflux boiling point.
6.5 Corrosion
6.5.1 Metal strip characteristics prior to testing
Prepare two sets of strips from each of the metals listed in Table B.1 (see Annex B), each strip having a
surface area of (25 ± 5) cm (approximately 8 cm long, 1,3 cm wide, and not more than 0,6 cm thick). Drill a
hole of between 4 mm and 5 mm in diameter and about 6 mm from one end of each strip. With the exception
of the tinned iron strips, clean the strips by abrading them on all surface areas with 320A or P400 waterproof
carborundum paper and ethanol (laboratory grade) until all surface scratches, cuts and pits are removed
from the strips, using a new piece of carborundum paper for each different type of metal. Wash the strips,
including the tinned iron, with ethanol (laboratory grade), then dry them with a clean lint-free cloth and
place them in a desiccator containing desiccant maintained at (23 ± 5) °C for at least 1 h. Handle the strips
with clean forceps after polishing to avoid fingerprint contamination.
Determine the mass of each strip to the nearest 0,1 mg and assemble each set of strips on an uncoated
steel cotter pin or bolt in the following order, so that the strips are in electrical contact: tinned iron, steel,
aluminium, cast iron, brass and copper. Bend the strips, except for the cast iron, so that there is a separation
of approximately 10 mm between two adjacent strips at their free ends. Immerse the strip assemblies in
ethanol (laboratory grade) to eliminate fingerprints (see Annex C).
6.5.2 Preparation of joints
Measure the base diameter of two standard SBR cups (follow Annex A), using an optical comparator or
micrometer, to the nearest 0,02 mm, along the centreline of the ISO and rubber type identifications and at
right angles to this centreline. Take the measurements at least 0,4 mm and not more than 2,4 mm above the
bottom edge and parallel to the base of the cup. Discard any cup if the two measured diameters differ by
more than 0,08 mm. Take the average of the measurements on each cup. Determine the hardness of each cup
thus supported by the procedure according to ISO 48-2:2018 (see Annex A). Determine the volume change
using the method given in 6.10.
Alternatively, the test may be carried out on rubber anvils prepared from the same material and having
the same properties as the cups. Place one rubber cup, with lip edge facing up, in each of two straight-sided
4)
round glass jars having a capacity of approximately 475 ml and inner dimensions of approximately 100 mm
height and 75 mm diameter. Apply four wrappings of 15 mm PTFE tape around the jar threads allowing
3 mm above the top of the jar. Use only tinned steel lids vented with a hole (0,8 ± 0,1) mm in diameter.
Insert a metal strip assembly inside each cup with the pinned end in contact with the concavity of the cup
and the free end extending upward in the jar. Mix 760 ml of the fluid with 40 ml of distilled water.
4) Suitable jars (RM-49) and lids (RM-64) are available from Society of Automotive Engineers (SAE), 400 Commonwealth
Drive, Warendale, Pa 15096, USA. Jars (RM 49) and lids (RM 64) are examples of suitable products available commercially.
This information is given for the convenience of users of this document and does not constitute an endorsement by ISO of
these products.
ISO/DIS 4925:2025(en)
6.5.3 Test procedure
Add a sufficient amount of the mixture to cover the metal strip assembly in each jar to a depth of
approximately 10 mm above the tops of the strips. Tighten the lids and place the jars in an oven maintained
at (100 ± 2) °C for (120 ± 2) h then allow the jars to cool at (23 ± 5) °C for 60 min to 90 min. Immediately
following the cooling period, remove the metal strips from the jars by use of forceps, removing loose
adhering sediment by agitation of the metal strip assembly in the fluid in the jar. Examine the test strips and
test jars for adhering crystalline deposit. Disassemble the metal strips, remove adhering fluid by flushing
with water and clean individual strips by wiping with a cloth for evidence of deterioration. Place the strips
in a desiccator containing a desiccant maintained at (23 ± 5) °C for at least 1 h.
Determine the mass of each strip to the nearest 0,1 mg. Determine the difference in mass of each metal
strip and divide the difference by the total surface area of the metal strip measured in square centimetres.
Average the measured values of the duplicates. In the event of a marginal pass on inspection, or of a failure
in only one of the duplicates, another set of duplicate test samples shall be run. Both repeat samples shall
meet all the requirements of Table 1.
Immediately following the cooling period, remove the rubber cups from the jars by use of forceps, removing
loose adhering sediment by agitation of the cup in the fluid in the jar. Rinse the cups in ethanol (laboratory
grade) and dry them in air. Examine the cups for evidence of sloughing, blisters, and other forms of
disintegration. Measure the base diameter, hardness and volume of each cup within 15 min after removal
from the fluid and calculate the changes according to 6.10.
Examine the fluid/water mixture in the jars for presence of gel. Agitate the fluid in the jars to suspend and
uniformly disperse sediment and transfer a 100 ml portion of this fluid to a cone-shaped centrifuge tube.
Determine the percentage sediment in accordance with ASTM D 91. Measure the pH of the corrosion test
fluid in accordance with 6.3.
6.6 Fluidity and appearance at low temperatures
6.6.1 At −40 °C for 144 h
5)
Place 100 ml of fluid in a glass sample bottle having a capacity of approximately 125 ml, an outside diameter
of (37 ± 0,5) mm and an overall height of (165 ± 2,5) mm. Stopper the bottle with a cork and place in a cold
bath maintained at (−40 ± 2) °C for (144 ± 4) h.
Examine the fluid for evidence of stratification and sedimentation. Invert the bottle and determine the
number of seconds required for the air bubble to travel to the top of the fluid.
6.6.2 At −50 °C for 6 h
Repeat the procedure and observations according to 6.6.1 but maintain the cold bath at (−50 ± 2) °C for
(6 ± 0,2) h.
6.7 Water tolerance
6.7.1 At −40 °C for 22 h
Mix 3,5 ml of distilled water with 100 ml of fluid and pour the mixture into a cone-shaped centrifuge tube.
Stopper the tube with a cork and place in a cold bath maintained at (−40 ± 2) °C for (22 ± 2) h.
Examine the fluid for evidence of stratification and sedimentation. Invert the tube and determine the number
of seconds required for the air bubble to travel to the top of the fluid. The air bubble shall be considered to
have reached the top of the fluid when the top of the bubble reaches the 2 ml graduation of the centrifuge tube.
5) Sample bottles (RM-59A) may be obtained from the Society of Automotive Engineers (SAE), 400 Commonwealth
Drive, Warrendale, Pa 15096, USA. Sample bottles (RM-59A) are an example of a suitable product available commercially.
This information is given for the convenience of users of this document and does not constitute an endorsement by ISO of
this product.
ISO/DIS 4925:2025(en)
6.7.2 At 60 °C for 22 h
Place the centrifuge tube from 6.7.1 in an oven maintained at (60 ± 2) °C for (22 ± 2) h. Remove the tube from
the oven and immediately examine the contents for evidence of stratification. Determine the percentage
sediment by volume in accordance with ASTM D 91.
6.8 Compatibility/miscibility with ISO 4926 fluid
6.8.1 At −40 °C for 22 h
Mix 50 ml of fluid with 50 ml of the fluid as specified in ISO 4926 and pour this mixture into a cone-shaped
centrifuge tube and stopper with a cork. Place the centrifuge tube for (22 ± 2) h in a bath maintained at
(−40 ± 2) °C. Examine the fluid for stratification and sedimentation.
6.8.2 At 60 °C for 22 h
Place the centrifuge tube specified in 6.8.1 in an oven maintained at (60 ± 2) °C for (22 ± 2) h. Remove the
tube from the oven and immediately examine the contents for evidence of stratification. Determine the
percentage sediment by volume in accordance with ASTM D 91.
6.9 Resistance to oxidation
Prepare two sets of aluminium and cast-iron test strips using the procedure given in 6.5. Determine the
mass of each strip to the nearest 0,1 mg and assemble a strip of each metal on an uncoated steel cotter
6)
pin or bolt, separating the strips at each end with a piece of tinfoil (99,9 % tin, 0,025 % lead, maximum)
approximately 12 mm square and between 0,02 mm and 0,06 mm in thickness.
Place (30 ± 1) ml of fluid in a small glass bottle approximately 120 ml in capacity. Add (60 ± 2) mg of reagent
grade benzoyl peroxide and (1,5 ± 0,05) ml of distilled water to the bottle. Benzoyl peroxide that has more
than 90 % purity (excluding water) when tested according to ASTM E 298 shall be used; brownish or dusty
product shall be discarded. Stopper the bottle and shake the contents, avoiding contact of the solution with
the stopper. Place the bottle in an oven at (70 ± 2) °C for (120 ± 10) min, shaking every 15 min to effect
solution of the peroxide. Remove the bottle from the oven, do not disturb the stopper, and cool in air at a
temperature of (23 ± 5) °C for 2 h.
Place approximately 1/8 section of a standard SBR cup, as described in Annex A, in the bottom of each of
two test tubes about 22 mm in diameter and 175 mm in length. Add 10 ml of prepared test fluid to each test
tube. Place a metal strip assembly in each tube with the end of the strips resting on the rubber, the solution
covering about one half of the length of the strips, and the end having the cotter pin remaining out of the
solution. Stopper the tubes with corks and store upright for (70 ± 2) h at (23 ± 5) °C. Loosen the stoppers and
place the tubes for (168 ± 2) h in an oven maintained at (70 ± 2) °C.
After the heating period, remove and disassemble the metal strips and examine for gum deposits. Wipe the
strips with a cloth saturated with ethanol (laboratory grade) and examine for pitting or roughening of the
surface. Place the strips in a desiccator containing a desiccant maintained at (23 ± 5) °C for at least 1 h.
Determine the mass of each strip to the nearest 0,1 mg.
Determine the mass change by dividing the difference in mass of each metal strip by the total surface area
of each metal strip measured in square centimetres. Average the measured values of the duplicates. In the
event of a marginal pass on inspection, or of a failure in only one of the duplicates, another set of duplicate
test samples shall be run. Both repeat samples shall meet all the requirements of Table 1.
6) Tinfoil (RM-27) may be obtained from the Society of
...

FINAL DRAFT
International
Standard
ISO/TC 22/SC 33
Road vehicles — Specification of
Secretariat: DIN
non-petroleum-based brake fluids
Voting begins on:
for hydraulic systems
2026-03-09
Véhicules routiers — Spécifications pour liquides de frein à base
Voting terminates on:
non pétrolière pour systèmes hydrauliques
2026-05-04
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 22/SC 33
Road vehicles — Specification of
Secretariat: DIN
non-petroleum-based brake fluids
Voting begins on:
for hydraulic systems
Véhicules routiers — Spécifications pour liquides de frein à base
Voting terminates on:
non pétrolière pour systèmes hydrauliques
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
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Phone: [phone]
Email: [e-mail]
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Published in Switzerland Reference number
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Materials . 2
5 Specifications . 2
6 Test methods . 4
6.1 Viscosity .4
6.1.1 General .4
6.1.2 Repeatability (single analyst) .5
6.1.3 Reproducibility (multi-laboratory) .5
6.2 Equilibrium reflux boiling point (ERBP) .5
6.2.1 General .5
6.2.2 Preparation of apparatus .5
6.2.3 Test procedure.5
6.2.4 Repeatability (single analyst) .5
6.2.5 Reproducibility (multi-laboratory) .6
6.2.6 Wet ERBP test .6
6.3 pH .9
6.4 Fluid stability .9
6.4.1 High-temperature stability .9
6.4.2 Chemical stability .10
6.5 Corrosion .10
6.5.1 Metal strip characteristics prior to testing .10
6.5.2 Preparation of joints .10
6.5.3 Test procedure.11
6.6 Fluidity and appearance at low temperatures .11
6.6.1 At −40 °C for 144 h .11
6.6.2 At −50 °C for 6 h .11
6.7 Water tolerance .11
6.7.1 At −40 °C for 22 h .11
6.7.2 At 60 °C for 22 h. 12
6.8 Compatibility and miscibility with ISO 4926 fluid . 12
6.8.1 At −40 °C for 22 h . 12
6.8.2 At 60 °C for 22 h. 12
6.9 Resistance to oxidation . 12
6.10 Effect on rubber . 13
6.10.1 Test procedures . 13
6.10.2 Repeatability (single analyst) .14
6.10.3 Reproducibility (multi-laboratory) .14
6.11 Reserve alkalinity in accordance with ASTM D 1121 .14
6.12 Resistance to friction-induced noise.14
6.13 Resistance to friction induced wear .14
Annex A (normative) ISO 4925 styrene-butadiene rubber (SBR) brake cups for testing brake
fluid .15
Annex B (normative) Corrosion test strips.18
Annex C (informative) Corrosion strip assembly . 19
Annex D (normative) Standard ethylene, propylene and diene monomer (EPDM) terpolymer
rubber slabstock .20

iii
Annex E (normative) Triethylene glycol monomethyl ether (TEGME) brake fluid grade.22
Annex F (normative) Wear test in the translatory oscillation tribometer to quantify the
friction-induced wear of a brake fluid in EPDM-metal contact .25
Bibliography .29

iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee 33, Vehicle
dynamics, chassis components and driving automation systems testing.
[1]
This fourth edition cancels and replaces the third edition (ISO 4925:2020 ), which has been technically
revised.
The main changes are as follows:
— lubrication requirement for noise test is added as a pass/fail criterion 6.12;
— lubrication requirement for wear test is added as a pass/fail criterion 6.13.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
Introduction
The specifications for fluids given in this document incorporate a range of performance standards in use
throughout the world at the time of publication. Further lubrication requirements are added for all classes 3,
4, 5–1, 6 and 7.
These fluids are mainly used in the hydraulic brake and clutch systems of road vehicles, but they can also be
used in any suitable hydraulic system.

vi
FINAL DRAFT International Standard ISO/FDIS 4925:2026(en)
Road vehicles — Specification of non-petroleum-based brake
fluids for hydraulic systems
1 Scope
This document provides the specifications, requirements and test methods for non-petroleum-based fluids
used in road-vehicle hydraulic brake and clutch systems that are designed for use with such fluids and
equipped with seals, cups or double-lipped type gland seals made of styrene-butadiene rubber (SBR) and
ethylene-propylene elastomer (EPDM).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 37, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties
ISO 48-2, Rubber, vulcanized or thermoplastic — Determination of hardness — Part 2: Hardness between 10
IRHD and 100 IRHD
ISO 815-1, Rubber, vulcanized or thermoplastic — Determination of compression set — Part 1: At ambient or
elevated temperatures
ISO 815-2, Rubber, vulcanized or thermoplastic — Determination of compression set — Part 2: At low
temperatures
ISO 3104, Petroleum products — Transparent and opaque liquids — Determination of kinematic viscosity and
calculation of dynamic viscosity
ISO 4926, Road vehicles — Hydraulic braking systems — Non-petroleum-based reference fluid
ASTM A 624, Standard specification for tin mill products, electrolytic tin plate, single reduced
ASTM D 91, Standard test method for precipitation number of lubricating oils
ASTM D 395, Standard test methods for rubber property — Compression set
ASTM D 412, Standard test methods for vulcanized rubber and thermoplastic elastomers — Tension
ASTM D 746, Standard test method for brittleness temperature of plastics and elastomers by impact
ASTM D 865, Standard test method for rubber — Deterioration by heating in air (test tube enclosure)
ASTM D 1120, Standard test method for boiling point of engine coolants
ASTM D 1121, Standard test method for reserve alkalinity of engine coolants and antirusts
ASTM D 1123, Standard test methods for water in engine coolant concentrate by the Karl Fisher reagent method
ASTM D 1415, Standard test method for rubber property — International hardness
ASTM D 3182, Standard practice for rubber — Materials, equipment and procedures for mixing standard
compounds and preparing standard vulcanized sheets

ASTM D 3185, Standard test methods for rubber—Evaluation of SBR (Styrene-Butadiene Rubber) including
mixtures with oil
ASTM D 3185:2006, Standard test methods for rubber — Evaluation of SBR (Styrene-Butadiene Rubber)
including mixtures with oil
ASTM E 298, Standard test methods for assay of organic peroxides
DIN 51834-5:2024, Testing of lubricants - Tribological test in the translatory oscillation apparatus - Part 5:
Quantification of the friction-induced noise development of brake fluids in EPDM-metal contacts
DIN 51834-5, Testing of lubricants - Tribological test in the translatory oscillation apparatus - Part 5:
Quantification of the friction-induced noise development of brake fluids in EPDM-metal contacts
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Materials
On visual inspection, the fluid shall be clear and free of suspended matter, dirt and sediment. The quality of
the materials used shall be such that the resulting product conforms to the requirements of this document
and that uniformity of performance is ensured. Fluids may be dyed, provided no confusion is possible
between them and other types of fluids.
5 Specifications
The product shall meet the requirements for the appropriate class in accordance with Table 1, using the test
methods according to Clause 6.
Table 1 — Brake fluid specifications — Tests and requirements
Requirement(s)
Test
method Test description Unit
Class Class Class Class Class
(subclause)
3 4 5–1 6 7
6.1 Viscosity
at −40 °C mm /s ≤1 500 ≤900 ≤750 ≤750
at 100 °C mm /s ≥1,5
6.2 Equilibrium reflux boiling point (ERBP) °C ≥205 ≥230 ≥260 ≥250 ≥260
6.2.6 Wet ERBP °C ≥140 ≥155 ≥180 ≥165 ≥180
6.3 pH — 7 to 11,5
6.4 Fluid stability
6.4.1 High-temperature stability °C ±5 °C
6.4.2 Chemical stability °C ±5 °C
6.5 Corrosion
Metal strip characteristics after testing
Mass change
TTaabblle 1 e 1 ((ccoonnttiinnueuedd))
Requirement(s)
Test
method Test description Unit
Class Class Class Class Class
(subclause)
3 4 5–1 6 7
Tinned iron mg/cm −0,2 to 0,2
Steel mg/cm −0,2 to 0,2
Aluminium mg/cm −0,1 to 0,1
Cast iron mg/cm −0,2 to 0,2
Brass mg/cm −0,4 to 0,4
Copper mg/cm −0,4 to 0,4
Aspect — No pitting or roughness outside
contact area
Staining/discolouration — Permitted
Liquid characteristics after testing
Aspect — No gel, none adhering crystals
pH — 7 to 11,5
Sediment % vol. ≤0,1
Rubber cup characteristics after testing
Blisters or carbon black separation at — None
surface
Hardness decrease IRHD ≤15
Base diameter increase mm ≤1,4
Volume increase % ≤16
6.6 Fluidity and appearance at low temperatures
6.6.1 at −40 °C for 144 h
Aspect — Clear and homogeneous
Bubble flow time s ≤10
Sediments — Absence
6.6.2 at −50 °C for 6 h
Aspect — Clear and homogeneous
Bubble flow time s ≤35
Sediments — Absence
6.7 Water tolerance
6.7.1 at −40 °C for 22 h
Aspect — Clear and homogeneous
Bubble flow time s ≤10
Sediments — Absence
6.7.2 at 60 °C for 22 h
Aspect — Clear and homogeneous
Sediments % vol. ≤0,05
6.8 Compatibility/miscibility with ISO 4926 fluid
6.8.1 at − 40 °C for 22 h
Aspect — Clear and homogeneous
Sediments — Absence
6.8.2 at 60 °C for 22 h
Aspect — Clear and homogeneous
Sediments % vol. ≤0,05
TTaabblle 1 e 1 ((ccoonnttiinnueuedd))
Requirement(s)
Test
method Test description Unit
Class Class Class Class Class
(subclause)
3 4 5–1 6 7
6.9 Resistance to oxidation
Metal strip aspect No pitting or roughness
—
no more than a trace of gum
Staining/discolouration — Permitted
Mass change of aluminium strip mg/cm −0,05 to +0,05
Mass change of cast iron strip mg/cm −0,3 to +0,3
6.10 Effect on rubber
6.10.1.2 Styrene butadiene rubber (SBR)
at 120 °C
Cup diameter increase mm 0,15 to 1,4
Hardness change IRHD −15 to 0
Volume increase % 1 to 16
Blisters or carbon black separation at None
—
surface
6.10.1.3 Ethylene propylene diene monomer (EPDM)
at 120 °C
Hardness change IRHD −15 to 0
Volume change % 0 to 10
Blisters or carbon black separation at None
—
surface
6.11 Reserve alkalinity in accordance with ASTM D 1121 ml to be reported
6.12 Resistance to friction introduced noise
Stick-slip oscillations, sigma — < 0,005
Static friction coefficient (SFC) — to be reported
6.13 Resistance to friction induced wear
Wear depth of EPDM disc: d mm < 0,18
wear
Load cycles before friction jump: n — to be reported
jump
Average friction coefficient: µ — to be reported
mean
6 Test methods
6.1 Viscosity
6.1.1 General
Determine the kinematic viscosity of the fluid in accordance with ISO 3104.
2 2
Report the viscosity to the nearest 1 mm /s at −40 °C and to the nearest 0,01 mm /s at +100 °C. Duplicate
runs that agree within 1,2 % relative are acceptable for averaging (95 % confidence level).

6.1.2 Repeatability (single analyst)
The coefficient of variation of results (each the average of duplicates) obtained by the same analyst on
different days shall not be greater than 0,4 % at 47 degrees of freedom. Two such values shall be considered
unacceptable (95 % confidence level) if they differ by more than 1,2 %.
6.1.3 Reproducibility (multi-laboratory)
The coefficient of variation of results (each the average of duplicates) obtained by analysts in different
laboratories shall not be greater than 1,0 % at 15 degrees of freedom. Two such values shall be considered
unacceptable (95 % confidence level) if they differ by more than 3,0 %.
6.2 Equilibrium reflux boiling point (ERBP)
6.2.1 General
1)
Determine the ERBP of the fluid in accordance with ASTM D 1120 , but with the following changes to the
procedure and to the apparatus (see Figure 1 and Figure 2).
— Thermometer: immersion shall be 76 mm and the thermometer shall be calibrated.
— Heat source: use either a suitable variac-controlled heating mantle designed to fit the flask, or an electric
heater with rheostat heat control.
6.2.2 Preparation of apparatus
Thoroughly clean and dry all glassware before use. Attach the flask to the condenser. When using a heating
mantle, place the mantle under the flask and support it with a suitable ring clamp and laboratory-type
stand, holding the whole assembly in place by a clamp. When using a rheostat-controlled heater, centre a
standard porcelain or other suitable refractory having a diameter opening of 32 mm to 38 mm over the
heating element of the electric heater and mount the flask on the refractory so that direct heat is applied to
the flask only through the opening in the refractory. Place the whole assembly in an area free from draughts
or other causes of sudden temperature changes.
6.2.3 Test procedure
Turn on the cooling water for the condenser and apply heat to the flask at such a rate that the fluid is refluxing
within (10 ± 2) min at a rate higher than one drop per second. The reflux rate shall not exceed five drops
per second. Immediately adjust the heat input to obtain a specified equilibrium reflux rate of one drop per
second to two drops per second over the next (5 ± 2) min period. Maintain a timed and constant equilibrium
reflux rate of one drop per second to two drops per second for an additional 2 min; record the average value
of four temperature readings taken at 30 s intervals at the equilibrium reflux boiling point.
Report the boiling point to the nearest degree Celsius. Duplicate results that agree within 3 °C are acceptable
for averages (95 % confidence level).
6.2.4 Repeatability (single analyst)
The standard deviation of results (each the average of duplicates), obtained by the same analyst on
different days shall not be greater than 1,3 °C at 34 degrees of freedom. Two such values shall be considered
unacceptable (95 % confidence level) if they differ by more than 4 °C.
1) Boiling chips are available from Electro Minerals Co. (US) or from the Society of Automotive Engineers (SAE). This
information is given for the convenience of users of this document and does not constitute an endorsement by ISO of the
products named. Equivalent products may be used if they can be shown to lead to the same results.

6.2.5 Reproducibility (multi-laboratory)
The standard deviation of results (each the average of duplicates), obtained by analysts in different
laboratories, shall be not greater than 3,5 °C at 15 degrees of freedom. Two such values shall be considered
unacceptable (95 % confidence level) if they differ by more than 10,5 °C.
6.2.6 Wet ERBP test
6.2.6.1 Apparatus
6.2.6.1.1 Two corrosion test jars or equivalent screw-top, straight-sided, round glass jars each having
a capacity of about 475 ml and approximate inner dimensions of 100 mm height by 75 mm diameter, with
2)
matching lids having new, clean inserts providing water-proof and vapour-proof seals .
6.2.6.1.2 Desiccator and cover, bowl-form glass desiccator with 250 mm inside diameter, having a
matching tubulated cover fitted with a No. eight rubber stopper (see Figure 3).
6.2.6.1.3 Desiccator plate of 230 mm diameter, perforated porcelain desiccator plate, without feet, glazed
3)
on one side (No.18 or equivalent).
2) Suitable corrosion test jars (RM-49) and tinned steel lids (RM-63) can be obtained from SAE, 400 Commonwealth
Drive, Warrendale, PA 15096, USA.
3) Desiccator plates (No. 08-641C) can be obtained from Fischer Scientific, Springfield, New Jersey, USA or CeramTec
[2]
AG (No. 602786), Glaswerk Wertheim KG (No. 911743431) or equivalents, according to ISO 12911 , diameter 235
mm. Corrosion test jars (RM-49), tinned steel lids (RM-63) and desiccator plates (No. 08-641C) are examples of suitable
products available commercially. This information is given for the convenience of users of this document and does not
constitute an endorsement by ISO of these products.

Dimensions in millimetres
Key
1 water outlet
2 water jacket
3 thermometer
4 plastic screw cap or rubber sleeve
5 boiling chips
6 19/38 joint
7 water inlet
Figure 1 — Boiling point test apparatus

Dimensions in millimetres
Key
1 19/38 joint
2 fire-polished
3 screw joint or rubber sleeve
a
Internal diameter: 8 to 9.
Figure 2 — Detail of 100 ml short-neck flask
6.2.6.2 Test procedure
To determine the wet ERBP of the fluid in duplicate (see Figure 3), first, humidify a 350 ml sample of the
fluid under controlled conditions, using 350 ml of triethylene glycol mono methyl ether (TEGME), follow
Annex E, to establish the end point for humidification.
Lubricate the ground-glass joint of the desiccator.
Then, pour (450 ± 10) ml of distilled water into the desiccator and insert the perforated porcelain plate.
Immediately place one open corrosion test jar containing (350 ± 5) ml of the humidified test fluid into the
desiccator. Place a second open corrosion test jar containing (350 ± 5) ml of TEGME control fluid into the same
desiccator. The water content of the TEGME control fluid at the start of exposure shall be (0,50 ± 0,05) % by
weight.
Next, replace the desiccator cover and place immediately in a forced ventilation oven set at (50 ± 1) °C.
Periodically, during oven humidification, remove the rubber stopper from the desiccator and, using a long-
needle hypodermic syringe, quickly sample the control fluid and determine its water content in accordance
with ASTM D 1123. A maximum of 10 ml of fluid shall be removed in total. When the water content of the
control fluid has reached (3,70 ± 0,05) % by weight, remove the desiccator from the oven and seal the test jar
promptly using a screw-cap jar lid. Allow the sealed jar to cool for 60 min to 90 min at (23 ± 5) °C. Determine
the ERBP in accordance with 6.2.1 and 6.2.3.

Dimensions in millimetres
Key
1 rubber stopper
2 glass desiccator with tubulated cover
3 lubricated ground joint
4 TEGME (see Annex E)
5 corrosion test jars
6 fluid sample
7 porcelain desiccator plate
8 water
Figure 3 — Humidification apparatus
6.3 pH
Mix the fluid with an equal volume of a mixture 50 % ethanol and 50 % distilled water neutralized to a pH
of 7,0 ± 0,1. Determine the pH of the resulting solution electrometrically at (23 ± 5) °C, using a pH meter
equipped with a calibrated full range (0 to 14) glass electrode and a calomel reference electrode, as specified
[3]
in ASTM D 664 .
Clouding or muddiness of the resulting solution is permitted in the determination.
6.4 Fluid stability
6.4.1 High-temperature stability
To determine the high-temperature stability of the fluid, heat a fresh sample of the original test fluid to a
temperature of (185 ± 2) °C according to the procedure specified in 6.2.3 and maintain it at that temperature
for (120 ± 5) min before determining the boiling point of the fluid, also in accordance with 6.2.3. The
difference between this observed boiling point and the previously determined ERBP (see 6.2) shall be
considered as the change in boiling point of the fluid.

6.4.2 Chemical stability
To determine the chemical stability of the fluid, first, mix 30 ml of the fluid with 30 ml of the fluid in
accordance with ISO 4926. Determine the ERBP of this fluid mixture by use of the test apparatus specified
in 6.2, applying heat to the flask at such a rate that the fluid refluxes within (10 ± 2) min at a rate of between
one drop per second and five drops per second.
Record the maximum fluid temperature observed during the first minute after the fluid begins refluxing
at a rate higher than one drop per second. Over the next (15 ± 1) min, adjust and maintain the rate of reflux
to one drop per second to two drops per second. Maintain a timed and constant equilibrium reflux rate of
from one drop per second to two drops per second for an additional 2 min, recording the average value of
four temperature readings at 30 s intervals as the final equilibrium reflux boiling point. Chemical reversion
is evidenced by the change in temperature between the maximum fluid temperature recorded and the final
equilibrium reflux boiling point.
6.5 Corrosion
6.5.1 Metal strip characteristics prior to testing
Prepare two sets of strips from each of the metals listed in Table B.1 (see Annex B), each strip having a
surface area of (25 ± 5) cm (approximately 8 cm long, 1,3 cm wide, and not more than 0,6 cm thick). Drill a
hole of between 4 mm and 5 mm in diameter and about 6 mm from one end of each strip. With the exception
of the tinned iron strips, clean the strips by abrading them on all surface areas with 320A or P400 waterproof
carborundum paper and ethanol (laboratory grade) until all surface scratches, cuts and pits are removed
from the strips, using a new piece of carborundum paper for each different type of metal. Wash the strips,
including the tinned iron, with ethanol (laboratory grade), then dry them with a clean lint-free cloth and
place them in a desiccator containing desiccant maintained at (23 ± 5) °C for at least 1 h. Handle the strips
with clean forceps after polishing to avoid fingerprint contamination.
Determine the mass of each strip to the nearest 0,1 mg and assemble each set of strips on an uncoated
steel cotter pin or bolt in the following order, so that the strips are in electrical contact: tinned iron, steel,
aluminium, cast iron, brass and copper. Bend the strips, except for the cast iron, so that there is a separation
of approximately 10 mm between two adjacent strips at their free ends. Immerse the strip assemblies in
ethanol (laboratory grade) to eliminate fingerprints (see Annex C).
6.5.2 Preparation of joints
Measure the base diameter of two standard SBR cups (in accordance with Annex A), using an optical
comparator or micrometer, to the nearest 0,02 mm, along the centreline of the ISO and rubber type
identifications and at right angles to this centreline. Take the measurements at least 0,4 mm and not more
than 2,4 mm above the bottom edge and parallel to the base of the cup. Discard any cup if the two measured
diameters differ by more than 0,08 mm. Take the average of the measurements on each cup. Determine
the hardness of each cup, thus supported by the procedure in accordance with ISO 48-2 (see Annex A).
Determine the volume change using the method given in 6.10.
Alternatively, the test may be carried out on rubber anvils prepared from the same material and having
the same properties as the cups. Place one rubber cup, with lip edge facing up, in each of two straight-sided
4)
round glass jars having a capacity of approximately 475 ml and inner dimensions of approximately 100 mm
height and 75 mm diameter. Apply four wrappings of 15 mm PTFE tape around the jar threads allowing
3 mm above the top of the jar. Use only tinned steel lids vented with a hole (0,8 ± 0,1) mm in diameter.
Insert a metal strip assembly inside each cup with the pinned end in contact with the concavity of the cup
and the free end extending upward in the jar. Mix 760 ml of the fluid with 40 ml of distilled water.
4) Suitable jars (RM-49) and lids (RM-64) are available from SAE, 400 Commonwealth Drive, Warendale, PA 15096, USA.
Jars (RM 49) and lids (RM 64) are examples of suitable products available commercially. This information is given for the
convenience of users of this document and does not constitute an endorsement by ISO of these products.

6.5.3 Test procedure
Add a sufficient amount of the mixture to cover the metal strip assembly in each jar to a depth of
approximately 10 mm above the tops of the strips. Tighten the lids and place the jars in an oven maintained
at (100 ± 2) °C for (120 ± 2) h. Then allow the jars to cool at (23 ± 5) °C for 60 min to 90 min. Immediately
following the cooling period, remove the metal strips from the jars by use of forceps, removing loose
adhering sediment by agitation of the metal strip assembly in the fluid in the jar. Examine the test strips and
test jars for adhering crystalline deposit. Disassemble the metal strips, remove adhering fluid by flushing
with water and clean individual strips by wiping with a cloth for evidence of deterioration. Place the strips
in a desiccator containing a desiccant maintained at (23 ± 5) °C for at least 1 h.
Determine the mass of each strip to the nearest 0,1 mg. Determine the difference in mass of each metal
strip and divide the difference by the total surface area of the metal strip measured in square centimetres.
Average the measured values of the duplicates. In the event of a marginal pass on inspection, or of a failure
in only one of the duplicates, another set of duplicate test samples shall be run. Both repeat samples shall
meet all the requirements of 6.5 in Table 1.
Immediately following the cooling period, remove the rubber cups from the jars by use of forceps, removing
loose adhering sediment by agitation of the cup in the fluid in the jar. Rinse the cups in ethanol (laboratory
grade) and dry them in air. Examine the cups for evidence of sloughing, blisters and other forms of
disintegration. Measure the base diameter, hardness and volume of each cup within 15 min after removal
from the fluid and calculate the changes according to 6.10.
Examine the fluid and water mixture in the jars for presence of gel. Agitate the fluid in the jars to suspend
and uniformly disperse sediment and transfer a 100 ml portion of this fluid to a cone-shaped centrifuge
tube. Determine the percentage sediment in accordance with ASTM D 91. Measure the pH of the corrosion
test fluid in accordance with 6.3.
6.6 Fluidity and appearance at low temperatures
6.6.1 At −40 °C for 144 h
5)
Place 100 ml of fluid in a glass sample bottle having a capacity of approximately 125 ml, an outside diameter
of (37 ± 0,5) mm and an overall height of (165 ± 2,5) mm. Stopper the bottle with a cork and place in a cold
bath maintained at (−40 ± 2) °C for (144 ± 4) h.
Examine the fluid for evidence of stratification and sedimentation. Invert the bottle and determine the
number of seconds required for the air bubble to travel to the top of the fluid.
6.6.2 At −50 °C for 6 h
Repeat the procedure and observations in accordance with 6.6.1 but maintain the cold bath at (−50 ± 2) °C
for (6 ± 0,2) h.
6.7 Water tolerance
6.7.1 At −40 °C for 22 h
Mix 3,5 ml of distilled water with 100 ml of fluid and pour the mixture into a cone-shaped centrifuge tube.
Stopper the tube with a cork and place in a cold bath maintained at (−40 ± 2) °C for (22 ± 2) h.
Examine the fluid for evidence of stratification and sedimentation. Invert the tube and determine the number
of seconds required for the air bubble to travel to the top of the fluid. The air bubble shall be considered to
have reached the top of the fluid when the top of the bubble reaches the 2 ml graduation of the centrifuge
tube.
5) Sample bottles (RM-59A) may be obtained from SAE, 400 Commonwealth Drive, Warrendale, PA 15096, USA.
Sample bottles (RM-59A) are an example of a suitable product available commercially. This information is given for the
convenience of users of this document and does not constitute an endorsement by ISO of this product.

6.7.2 At 60 °C for 22 h
Place the centrifuge tube from 6.7.1 in an oven maintained at (60 ± 2) °C for (22 ± 2) h. Remove the tube from
the oven and immediately examine the contents for evidence of stratification. Determine the percentage
sediment by volume in accordance with ASTM D 91.
6.8 Compatibility and miscibility with ISO 4926 fluid
6.8.1 At −40 °C for 22 h
Mix 50 ml of fluid with 50 ml of the fluid in accordance with ISO 4926 and pour this mixture into a cone-
shaped centrifuge tube and stopper with a cork. Place the centrifuge tube for (22 ± 2) h in a bath maintained
at (−40 ± 2) °C. Examine the fluid for stratification and sedimentation.
6.8.2 At 60 °C for 22 h
Place the centrifuge tube specified in 6.8.1 in an oven maintained at (60 ± 2) °C for (22 ± 2) h. Remove the
tube from the oven and immediately examine the contents for evidence of stratification. Determine the
percentage sediment by volume in accordance with ASTM D 91.
6.9 Resistance to oxidation
Prepare two sets of aluminium and cast-iron test strips using the procedure given in 6.5. Determine the
mass of each strip to the nearest 0,1 mg and assemble a strip of each metal on an uncoated steel cotter
6)
pin or bolt, separating the strips at each end with a piece of tinfoil (99,9 % tin, 0,025 % lead, maximum)
approximately 12 mm square and between 0,02 mm and 0,06 mm in thickness.
Place (30 ± 1) ml of fluid in a small glass bottle approximately 120 ml in capacity. Add (60 ± 2) mg of reagent
grade benzoyl peroxide and (1,5 ± 0,05) ml of distilled water to the bottle. Benzoyl peroxide that has more
than 90 % purity (excluding water) when tested in accordance with ASTM E 298 shall be used; brownish or
dusty product shall be discarded. Stopper the bottle and shake the contents, avoiding contact of the solution
with the stopper. Place the bottle in an oven at (70 ± 2) °C for (120 ± 10) min, shaking every 15 min to effect
solution of the peroxide. Remove the bottle from the oven, do not disturb the stopper and cool in air at a
temperature of (23 ± 5) °C for 2 h.
Place approximately 1/8 section of a standard SBR cup, as described in Annex A, in the bottom of each of
two test tubes about 22 mm in diameter and 175 mm in length. Add 10 ml of prepared test fluid to each test
tube. Place a metal strip assembly in each tube with the end of the strips resting on the rubber, the solution
covering about one half of the length of the strips, and the end having the cotter pin remaining out of the
solution. Stopper the tubes with corks and store upright for (70 ± 2) h at (23 ± 5) °C. Loosen the stoppers and
place the tubes for (168 ± 2) h in an oven maintained at (70 ± 2) °C.
After the heating period, remove and disassemble the metal strips and examine for gum deposits. Wipe the
strips with a cloth saturated with ethanol (laboratory grade) and examine for pitting or roughening of the
surface. Place the strips in a desiccator containing a desiccant maintained at (23 ± 5) °C for at least 1 h.
Determine the mass of each strip to the nearest 0,1 mg.
Determine the mass change by dividing the difference in mass of each metal strip by the total surface area
of each metal strip measured in square centimetres. Average the me
...

ISO/TC 22/SC 33
Secretariat: DIN
Date: 2026-02-23
Road vehicles — Specification of non-petroleum-based brake fluids
for hydraulic systems
Véhicules routiers — Spécifications pour liquides de frein à base non pétrolière pour systèmes hydrauliques
FDIS stage
VVoottiing bng beegiginsns o on:n: 202 20255--0909--0404
VoVotinting tg teerrminminatateses o onn:: 22002255--1111--2727

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Materials . 2
5 Specifications . 2
6 Test methods . 5
6.1 Viscosity . 5
6.2 Equilibrium reflux boiling point (ERBP) . 6
6.3 pH . 10
6.4 Fluid stability . 10
6.5 Corrosion . 11
6.6 Fluidity and appearance at low temperatures . 12
6.7 Water tolerance . 13
6.8 Compatibility and miscibility with ISO 4926 fluid . 13
6.9 Resistance to oxidation . 13
6.10 Effect on rubber . 14
6.11 Reserve alkalinity in accordance with ASTM D 1121 . 15
6.12 Resistance to friction-induced noise . 15
6.13 Resistance to friction induced wear . 15
Annex A (normative) ISO 4925 styrene-butadiene rubber (SBR) brake cups for testing brake
fluid . 16
Annex B (normative) Corrosion test strips . 19
Annex C (informative) Corrosion strip assembly . 20
Annex D (normative) Standard ethylene, propylene and diene monomer (EPDM) terpolymer
rubber slabstock . 21
Annex E (normative) Triethylene glycol monomethyl ether (TEGME) brake fluid grade . 23
Annex F (normative) Wear test in the translatory oscillation tribometer to quantify the friction-
induced wear of a brake fluid in EPDM-metal contact . 26
Bibliography . 30

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO documentdocuments should be noted. This document was drafted in accordance with the editorial rules
of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee 33, Vehicle
dynamics, chassis components and driving automation systems testing.
[1]
This fourth edition cancels and replaces the third edition (ISO 4925 ), which has been technically revised.
The main changes are as follows:
— the note of intended introduction of a wear and noise test currently under development in the SAE and
ISO TF lubrication is replaced by introduction of these developed tests methods:
— lubrication requirement for noise test is added as a pass/fail criterion 6.12;6.12;
— lubrication requirement for wear test is added as a pass/fail criterion 6.13;6.13.
— editorial changes.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
The specifications for fluids given in this document incorporate a range of performance standards in use
throughout the world at the time of publication. Further lubrication requirements are added for all classes 3,
4, 5–1, 6 and 7.
The major use of theseThese fluids isare mainly used in the hydraulic brake and clutch systems of road
vehicles, but they can also be used in any suitable hydraulic system.
v
Road vehicles — Specification of non-petroleum-based brake fluids
for hydraulic systems
1 Scope
This document provides the specifications, requirements and test methods for non-petroleum-based fluids
used in road-vehicle hydraulic brake and clutch systems that are designed for use with such fluids and
equipped with seals, cups or double-lipped type gland seals made of styrene-butadiene rubber (SBR) and
ethylene-propylene elastomer (EPDM).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 37, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties
ISO 48-2, Rubber, vulcanized or thermoplastic — Determination of hardness — Part 2: Hardness between 10
IRHD and 100 IRHD
ISO 815-1, Rubber, vulcanized or thermoplastic — Determination of compression set — Part 1: At ambient or
elevated temperatures
ISO 815-2, Rubber, vulcanized or thermoplastic — Determination of compression set — Part 2: At low
temperatures
ISO 3104, Petroleum products — Transparent and opaque liquids — Determination of kinematic viscosity and
calculation of dynamic viscosity
ISO 4926, Road vehicles — Hydraulic braking systems — Non-petroleum-based reference fluid
ASTM D 3185:2006 A 624, Standard test methodsspecification for rubber—Evaluation of SBR (Styrene-
Butadiene Rubber) including mixtures with oiltin mill products, electrolytic tin plate, single reduced
ASTM D 91, Standard test method for precipitation number of lubricating oils
ASTM D 395, Standard test methods for rubber property — Compression set
ASTM D 412, Standard test methods for vulcanized rubber and thermoplastic elastomers — Tension
ASTM D 746, Standard test method for brittleness temperature of plastics and elastomers by impact
ASTM D 865, Standard test method for rubber — Deterioration by heating in air (test tube enclosure)
ASTM D 1120, Standard test method for boiling point of engine coolants
ASTM D 1121, Standard test method for reserve alkalinity of engine coolants and antirusts
ASTM D 1123, Standard test methods for water in engine coolant concentrate by the Karl Fisher reagent method
ASTM D 1415, Standard test method for rubber property — International hardness

ASTM D 3182, Standard practice for rubber — Materials, equipment and procedures for mixing standard
compounds and preparing standard vulcanized sheets
ASTM D 3185, Standard test methods for rubber—Evaluation of SBR (Styrene-Butadiene Rubber) including
mixtures with oil
ASTM D 3185:2006, Standard test methods for rubber — Evaluation of SBR (Styrene-Butadiene Rubber)
including mixtures with oil
ASTM E 298, Standard test methods for assay of organic peroxides
DIN 51834-5:2024, Testing of lubricants - Tribological test in the translatory oscillation apparatus - Part 5:
Quantification of the friction-induced noise development of brake fluids in EPDM-metal contacts
ISO 37, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties
ISO 48-2, Rubber, vulcanized or thermoplastic — Determination of hardness (hardness between 10 IRHD and
100 IRHD)
ISO 812, Rubber, vulcanized or thermoplastic — Determination of low-temperature brittleness
ISO 815 (all parts), Rubber, vulcanized or thermoplastic — Determination of compression set
ISO 3104, Petroleum products — Transparent and opaque liquids — Determination of kinematic viscosity and
calculation of dynamic viscosity
ISO 4926, Road vehicle — Hydraulic braking systems — Non petroleum base reference fluids
DIN 51834-5, Testing of lubricants - Tribological test in the translatory oscillation apparatus - Part 5:
Quantification of the friction-induced noise development of brake fluids in EPDM-metal contacts
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
4 Materials
On visual inspection, the fluid shall be clear and free of suspended matter, dirt and sediment. The quality of
the materials used shall be such that the resulting product conforms to the requirements of this document and
that uniformity of performance is ensured. Fluids may be dyed, provided no confusion is possible between
them and other types of fluids.
5 Specifications
The product shall meet the requirements for the appropriate class in accordance with Table 1, using the test
methods according to Clause 6.
Table 1 — Brake fluid specifications — Tests and requirements
Requirement(s)
Test
method
Clas Clas
Test description Unit
Clas Clas Clas
(subclaus
s 5– s 7
s 3 s 4 s 6
e)
6.16.1 Viscosity
at −40 °C mm /s ≤1 500 ≤900 ≤750 ≤750
at 100 °C mm /s ≥1,5
6.26.2 Equilibrium reflux boiling point (ERBP) °C ≥205 ≥230 ≥260 ≥250 ≥260
6.2.66.2.6 Wet ERBP °C ≥140 ≥155 ≥180 ≥165 ≥180
6.36.3 pH — 7 to 11,5
6.46.4 Fluid stability
6.4.16.4.1 High-temperature stability °C ±5 °C
6.4.26.4.2 Chemical stability °C ±5 °C
6.56.5 Corrosion
Metal strip characteristics after testing
Mass change
Tinned iron mg/cm −0,2 to 0,2
Steel mg/cm −0,2 to 0,2
Aluminium mg/cm −0,1 to 0,1
Cast iron mg/cm −0,2 to 0,2
Brass mg/cm −0,4 to 0,4
Copper mg/cm −0,4 to 0,4
Aspect — No pitting or roughness outside
contact area
Staining/discolorationdiscolouration — Permitted
Liquid characteristics after testing
Aspect — No gel, none adhering crystals
pH — 7 to 11,5
Sediment % vol. ≤0,1
Rubber cup characteristics after testing
Blisters or carbon black separation at — None
surface
Hardness decrease IRHD ≤15
Base diameter increase mm ≤1,4
Requirement(s)
Test
method
Clas Clas
Test description Unit
Clas Clas Clas
(subclaus
s 5– s 7
s 3 s 4 s 6
e)
Volume increase % ≤16
6.66.6 Fluidity and appearance at low temperatures
6.6.16.6.1  at −40 °C for 144 h
Aspect — Clear and homogeneous
Bubble flow time s ≤10
Sediments — Absence
6.6.26.6.2  at −50 °C for 6 h
Aspect — Clear and homogeneous
Bubble flow time s ≤35
Sediments — Absence
6.76.7 Water tolerance
6.7.16.7.1 at −40 °C for 22 h
Aspect — Clear and homogeneous
Bubble flow time s ≤10
Sediments — Absence
6.7.26.7.2 at 60 °C for 22 h
Aspect — Clear and homogeneous
Sediments % vol. ≤0,05
6.86.8 Compatibility/miscibility with ISO 4926 fluid
6.8.16.8.1 at − 40 °C for 22 h
Aspect — Clear and homogeneous
Sediments — Absence
6.8.26.8.2 at 60 °C for 22 h
Aspect — Clear and homogeneous
Sediments % vol. ≤0,05
6.96.9 Resistance to oxidation
Metal strip aspect No pitting or roughness
—
no more than a trace of gum
Staining/discolorationdiscolouration — Permitted
Mass change of aluminium strip mg/cm −0,05 to +0,05
Mass change of cast iron strip mg/cm −0,3 to +0,3
6.106.10 Effect on rubber
6.10.1.16.
Styrene butadiene rubber (SBR)
10.1.2
Requirement(s)
Test
method
Clas Clas
Test description Unit
Clas Clas Clas
(subclaus
s 5– s 7
s 3 s 4 s 6
e)
at 120 °C
Cup diameter increase mm 0,15 to 1,4
Hardness change IRHD −15 to 0
Volume increase % 1 to 16
Blisters or carbon black separation at None
—
surface
6.10.1.26.
Ethylene propylene diene monomer (EPDM)
10.1.3
at 120 °C
Hardness change IRHD −15 to 0
Volume change % 0 to 10
Blisters or carbon black separation at None
—
surface
6.116.11 Reserve alkalinity according toin accordance with to be reported
ml
ASTM D 1121
6.126.12 Resistance to friction introduced noise
Stick-slip oscillations, sigma — < 0,005
Static friction coefficient, (SFC) — to be reported
6.136.13 Resistance to friction induced wear

Wear depth of EPDM disc: d d mm < 0,18
wear wear
Load cycles before friction jump: njump — to be reported
Average friction coefficient: µmean — to be reported
6 Test methods
6.1 Viscosity
6.1.1 General
Determine the kinematic viscosity of the fluid in accordance with ISO 3104.
2 2
Report the viscosity to the nearest 1 mm /s at −40 °C and to the nearest 0,01 mm /s at +100 °C. Duplicate runs
that agree within 1,2 % relative are acceptable for averaging (95 % confidence level).
6.1.2 Repeatability (single analyst)
The coefficient of variation of results (each the average of duplicates) obtained by the same analyst on
different days shall not be greater than 0,4 % at 47 degrees of freedom. Two such values shall be considered
unacceptable (95 % confidence level) if they differ by more than 1,2 %.
6.1.3 Reproducibility (multi-laboratory)
The coefficient of variation of results (each the average of duplicates) obtained by analysts in different
laboratories shall not be greater than 1,0 % at 15 degrees of freedom. Two such values shall be considered
unacceptable (95 % confidence level) if they differ by more than 3,0 %.
6.2 Equilibrium reflux boiling point (ERBP)
6.2.1 General
1)
Determine the ERBP of the fluid in accordance with ASTM D 1120 , but with the following changes to the
procedure and to the apparatus (see Figure 1 and Figure 2).
— Thermometer: immersion shall be 76 mm and the thermometer shall be calibrated.
— Heat source: use either a suitable variac-controlled heating mantle designed to fit the flask, or an electric
heater with rheostat heat control.
6.2.2 Preparation of apparatus
Thoroughly clean and dry all glassware before use. Attach the flask to the condenser. When using a heating
mantle, place the mantle under the flask and support it with a suitable ring clamp and laboratory-type stand,
holding the whole assembly in place by a clamp. When using a rheostat-controlled heater, centre a standard
porcelain or other suitable refractory having a diameter opening of 32 mm to 38 mm over the heating element
of the electric heater and mount the flask on the refractory so that direct heat is applied to the flask only
through the opening in the refractory. Place the whole assembly in an area free from draughts or other causes
of sudden temperature changes.
6.2.3 Test procedure
Turn on the cooling water for the condenser and apply heat to the flask at such a rate that the fluid is refluxing
within (10 ± 2) min at a rate higher than one drop per second. The reflux rate shall not exceed five drops per
second. Immediately adjust the heat input to obtain a specified equilibrium reflux rate of one drop per second
to two drops per second over the next (5 ± 2) min period. Maintain a timed and constant equilibrium reflux
rate of one drop per second to two drops per second for an additional 2 min; record the average value of four
temperature readings taken at 30 s intervals at the equilibrium reflux boiling point.
Report the boiling point to the nearest degree Celsius. Duplicate results that agree within 3 °C are acceptable
for averages (95 % confidence level).
6.2.4 Repeatability (single analyst)
The standard deviation of results (each the average of duplicates), obtained by the same analyst on different
days shall not be greater than 1,3 °C at 34 degrees of freedom. Two such values shall be considered
unacceptable (95 % confidence level) if they differ by more than 4 °C.

1)
Boiling chips are available from Electro Minerals Co. (US) or from the Society of Automotive Engineers (SAE). This
information is given for the convenience of users of this document and does not constitute an endorsement by ISO of the
products named. Equivalent products may be used if they can be shown to lead to the same results.

6.2.5 Reproducibility (multi-laboratory)
The standard deviation of results (each the average of duplicates), obtained by analysts in different
laboratories, shall be not greater than 3,5 °C at 15 degrees of freedom. Two such values shall be considered
unacceptable (95 % confidence level) if they differ by more than 10,5 °C.
6.2.6 Wet ERBP test
6.2.6.1 Apparatus
6.2.6.1.1 Two corrosion test jars or equivalent screw-top, straight-sided, round glass jars each having a
capacity of about 475 ml and approximate inner dimensions of 100 mm height by 75 mm diameter, with
2)
matching lids having new, clean inserts providing water-proof and vapour-proof seals .
6.2.6.1.2 Desiccator and cover, bowl-form glass desiccator with 250 mm inside diameter, having a
matching tubulated cover fitted with a No. eight rubber stopper (see Figure 3).
6.2.6.1.3 Desiccator plate of 230 mm diameter, perforated porcelain desiccator plate, without feet, glazed
3) )
on one side (No.18 or equivalent)). .

2)
Suitable corrosion test jars (RM-49) and tinned steel lids (RM-63) can be obtained from the Society of Automotive
Engineers (SAE),, 400 Commonwealth Drive, Warrendale, PaPA 15096, USA.

3)
Desiccator plates (No. 08-641C) can be obtained from Fischer Scientific, Springfield, New Jersey, USA or CeramTec AG
[2]
(No. 602786), Glaswerk Wertheim KG (No. 911743431) or equivalents, according to DIN/ISOto ISO 12911, , diameter
235 mm. Corrosion test jars (RM-49), tinned steel lids (RM-63) and desiccator plates (No. 08-641C) are examples of
suitable products available commercially. This information is given for the convenience of users of this document and
does not constitute an endorsement by ISO of these products.

Dimensions in millimetres
Key
1 water outlet
2 water jacket
3 thermometer
4 plastic screw cap or rubber sleeve
5 boiling chips
6 19/38 joint
7 water inlet
Figure 1— Boiling point test apparatus
Dimensions in millimetres
Key
1 19/38 joint
2 fire-polished
3 screw joint or rubber sleeve
a
Internal diameter: 8 to 9.
Figure 2— Detail of 100 ml short-neck flask
6.2.6.2 Test procedure
To determine the wet ERBP of the fluid in duplicate (see Figure 3), first, humidify a 350 ml sample of the fluid
under controlled conditions, using 350 ml of triethylene glycol mono methyl ether (TEGME), follow Annex E,
to establish the end point for humidification.
Lubricate the ground-glass joint of the desiccator.
Then, pour (450 ± 10) ml of distilled water into the desiccator and insert the perforated porcelain plate.
Immediately place one open corrosion test jar containing (350 ± 5) ml of the humidified test fluid into the
desiccator. Place a second open corrosion test jar containing (350 ± 5) ml of TEGME control fluid into the same
desiccator. The water content of the TEGME control fluid at the start of exposure shall be (0,50 ± 0,05) % by
weight.
Next, replace the desiccator cover and place immediately in a forced ventilation oven set at (50 ± 1) °C.
Periodically, during oven humidification, remove the rubber stopper from the desiccator and, using a long-
needle hypodermic syringe, quickly sample the control fluid and determine its water content in accordance
with ASTM D 1123. A maximum of 10 ml of fluid shall be removed in total. When the water content of the
control fluid has reached (3,70 ± 0,05) % by weight, remove the desiccator from the oven and seal the test jar
promptly using a screw-cap jar lid. Allow the sealed jar to cool for 60 min to 90 min at (23 ± 5) °C. Determine
the ERBP in accordance with 6.2.1 and 6.2.3.
Dimensions in millimetres
Key
1 rubber stopper
2 glass desiccator with tubulated cover
3 lubricated ground joint
4 TEGME (see Annex E)
5 corrosion test jars
6 fluid sample
7 porcelain desiccator plate
8 water
Figure 3— Humidification apparatus
6.3 pH
Mix the fluid with an equal volume of a mixture 50 % ethanol and 50 % distilled water neutralized to a pH of
7,0 ± 0,1. Determine the pH of the resulting solution electrometrically at (23 ± 5) °C, using a pH meter
equipped with a calibrated full range (0 to 14) glass electrode and a calomel reference electrode, as specified
[3]
in ASTM D 664 .
Clouding or muddiness of the resulting solution is permitted in the determination.
6.4 Fluid stability
6.4.1 High-temperature stability
To determine the high-temperature stability of the fluid, heat a fresh sample of the original test fluid to a
temperature of (185 ± 2) °C according to the procedure specified in 6.2.3 and maintain it at that temperature
for (120 ± 5) min before determining the boiling point of the fluid, also in accordance with 6.2.3. The difference
between this observed boiling point and the previously determined ERBP (see 6.2) shall be considered as the
change in boiling point of the fluid.
6.4.2 Chemical stability
To determine the chemical stability of the fluid, first, mix 30 ml of the fluid with 30 ml of the fluid specified in
accordance with ISO 4926. Determine the ERBP of this fluid mixture by use of the test apparatus specified in
6.2, applying heat to the flask at such a rate that the fluid refluxes within (10 ± 2) min at a rate of between one
drop per second and five drops per second.
Record the maximum fluid temperature observed during the first minute after the fluid begins refluxing at a
rate higher than one drop per second. Over the next (15 ± 1) min, adjust and maintain the rate of reflux to one
drop per second to two drops per second. Maintain a timed and constant equilibrium reflux rate of from one
drop per second to two drops per second for an additional 2 min, recording the average value of four
temperature readings at 30 s intervals as the final equilibrium reflux boiling point. Chemical reversion is
evidenced by the change in temperature between the maximum fluid temperature recorded and the final
equilibrium reflux boiling point.
6.5 Corrosion
6.5.1 Metal strip characteristics prior to testing
Prepare two sets of strips from each of the metals listed in Table B.1 (see Annex B), each strip having a surface
area of (25 ± 5) cm (approximately 8 cm long, 1,3 cm wide, and not more than 0,6 cm thick). Drill a hole of
between 4 mm and 5 mm in diameter and about 6 mm from one end of each strip. With the exception of the
tinned iron strips, clean the strips by abrading them on all surface areas with 320A or P400 waterproof
carborundum paper and ethanol (laboratory grade) until all surface scratches, cuts and pits are removed from
the strips, using a new piece of carborundum paper for each different type of metal. Wash the strips, including
the tinned iron, with ethanol (laboratory grade), then dry them with a clean lint-free cloth and place them in
a desiccator containing desiccant maintained at (23 ± 5) °C for at least 1 h. Handle the strips with clean forceps
after polishing to avoid fingerprint contamination.
Determine the mass of each strip to the nearest 0,1 mg and assemble each set of strips on an uncoated steel
cotter pin or bolt in the following order, so that the strips are in electrical contact: tinned iron, steel,
aluminium, cast iron, brass and copper. Bend the strips, except for the cast iron, so that there is a separation
of approximately 10 mm between two adjacent strips at their free ends. Immerse the strip assemblies in
ethanol (laboratory grade) to eliminate fingerprints (see Annex C).
6.5.2 Preparation of joints
Measure the base diameter of two standard SBR cups (in accordance with Annex A), using an optical
comparator or micrometer, to the nearest 0,02 mm, along the centreline of the ISO and rubber type
identifications and at right angles to this centreline. Take the measurements at least 0,4 mm and not more
than 2,4 mm above the bottom edge and parallel to the base of the cup. Discard any cup if the two measured
diameters differ by more than 0,08 mm. Take the average of the measurements on each cup. Determine the
hardness of each cup, thus supported by the procedure according toin accordance with ISO 48-2:2018 (see
Annex A). Determine the volume change using the method given in 6.10.
Alternatively, the test may be carried out on rubber anvils prepared from the same material and having the
same properties as the cups. Place one rubber cup, with lip edge facing up, in each of two straight-sided round
4)
glass jars having a capacity of approximately 475 ml and inner dimensions of approximately 100 mm height

4)
Suitable jars (RM-49) and lids (RM-64) are available from Society of Automotive Engineers (SAE),, 400 Commonwealth
Drive, Warendale, PaPA 15096, USA. Jars (RM 49) and lids (RM 64) are examples of suitable products available
and 75 mm diameter. Apply four wrappings of 15 mm PTFE tape around the jar threads allowing 3 mm above
the top of the jar. Use only tinned steel lids vented with a hole (0,8 ± 0,1) mm in diameter.
Insert a metal strip assembly inside each cup with the pinned end in contact with the concavity of the cup and
the free end extending upward in the jar. Mix 760 ml of the fluid with 40 ml of distilled water.
6.5.3 Test procedure
Add a sufficient amount of the mixture to cover the metal strip assembly in each jar to a depth of approximately
10 mm above the tops of the strips. Tighten the lids and place the jars in an oven maintained at (100 ± 2) °C
for (120 ± 2) h then. Then allow the jars to cool at (23 ± 5) °C for 60 min to 90 min. Immediately following the
cooling period, remove the metal strips from the jars by use of forceps, removing loose adhering sediment by
agitation of the metal strip assembly in the fluid in the jar. Examine the test strips and test jars for adhering
crystalline deposit. Disassemble the metal strips, remove adhering fluid by flushing with water and clean
individual strips by wiping with a cloth for evidence of deterioration. Place the strips in a desiccator containing
a desiccant maintained at (23 ± 5) °C for at least 1 h.
Determine the mass of each strip to the nearest 0,1 mg. Determine the difference in mass of each metal strip
and divide the difference by the total surface area of the metal strip measured in square centimetres. Average
the measured values of the duplicates. In the event of a marginal pass on inspection, or of a failure in only one
of the duplicates, another set of duplicate test samples shall be run. Both repeat samples shall meet all the
requirements of Table 1, 6.5.6.5 in Table 1.
Immediately following the cooling period, remove the rubber cups from the jars by use of forceps, removing
loose adhering sediment by agitation of the cup in the fluid in the jar. Rinse the cups in ethanol (laboratory
grade) and dry them in air. Examine the cups for evidence of sloughing, blisters and other forms of
disintegration. Measure the base diameter, hardness and volume of each cup within 15 min after removal from
the fluid and calculate the changes according to 6.10.6.10.
Examine the fluid/ and water mixture in the jars for presence of gel. Agitate the fluid in the jars to suspend
and uniformly disperse sediment and transfer a 100 ml portion of this fluid to a cone-shaped centrifuge tube.
Determine the percentage sediment in accordance with ASTM D 91. Measure the pH of the corrosion test fluid
in accordance with 6.3.
6.6 Fluidity and appearance at low temperatures
6.6.1 At −40 °C for 144 h
5)
Place 100 ml of fluid in a glass sample bottle having a capacity of approximately 125 ml, an outside diameter
of (37 ± 0,5) mm and an overall height of (165 ± 2,5) mm. Stopper the bottle with a cork and place in a cold
bath maintained at (−40 ± 2) °C for (144 ± 4) h.
Examine the fluid for evidence of stratification and sedimentation. Invert the bottle and determine the number
of seconds required for the air bubble to travel to the top of the fluid.

commercially. This information is given for the convenience of users of this document and does not constitute an
endorsement by ISO of these products.

5)
Sample bottles (RM-59A) may be obtained from the Society of Automotive Engineers (SAE),, 400 Commonwealth Drive,
Warrendale, PaPA 15096, USA. Sample bottles (RM-59A) are an example of a suitable product available commercially.
This information is given for the convenience of users of this document and does not constitute an endorsement by ISO
of this product.
6.6.2 At −50 °C for 6 h
Repeat the procedure and observations according to 6.6.1in accordance with 6.6.1 but maintain the cold bath
at (−50 ± 2) °C for (6 ± 0,2) h.
6.7 Water tolerance
6.7.1 At −40 °C for 22 h
Mix 3,5 ml of distilled water with 100 ml of fluid and pour the mixture into a cone-shaped centrifuge tube.
Stopper the tube with a cork and place in a cold bath maintained at (−40 ± 2) °C for (22 ± 2) h.
Examine the fluid for evidence of stratification and sedimentation. Invert the tube and determine the number
of seconds required for the air bubble to travel to the top of the fluid. The air bubble shall be considered to
have reached the top of the fluid when the top of the bubble reaches the 2 ml graduation of the centrifuge tube.
6.7.2 At 60 °C for 22 h
Place the centrifuge tube from 6.7.1 in an oven maintained at (60 ± 2) °C for (22 ± 2) h. Remove the tube from
the oven and immediately examine the contents for evidence of stratification. Determine the percentage
sediment by volume in accordance with ASTM D 91.
6.8 Compatibility/ and miscibility with ISO 4926 fluid
6.8.1 At −40 °C for 22 h
Mix 50 ml of fluid with 50 ml of the fluid as specified in accordance with ISO 4926 and pour this mixture into
a cone-shaped centrifuge tube and stopper with a cork. Place the centrifuge tube for (22 ± 2) h in a bath
maintained at (−40 ± 2) °C. Examine the fluid for stratification and sedimentation.
6.8.2 At 60 °C for 22 h
Place the centrifuge tube specified in 6.8.1 in an oven maintained at (60 ± 2) °C for (22 ± 2) h. Remove the tube
from the oven and immediately examine the contents for evidence of stratification. Determine the percentage
sediment by volume in accordance with ASTM D 91.
6.9 Resistance to oxidation
Prepare two sets of aluminium and cast-iron test strips using the procedure given in 6.5. Determine the mass
of each strip to the nearest 0,1 mg and assemble a strip of each metal on an uncoated steel cotter pin or bolt,
6)
separating the strips at each end with a piece of tinfoil (99,9 % tin, 0,025 % lead, maximum) approximately
12 mm square and between 0,02 mm and 0,06 mm in thickness.
Place (30 ± 1) ml of fluid in a small glass bottle approximately 120 ml in capacity. Add (60 ± 2) mg of reagent
grade benzoyl peroxide and (1,5 ± 0,05) ml of distilled water to the bottle. Benzoyl peroxide that has more
than 90 % purity (excluding water) when tested according toin accordance with ASTM E 298 shall be used;
brownish or dusty product shall be discarded. Stopper the bottle and shake the contents, avoiding contact of
the solution with the stopper. Place the bottle in an oven at (70 ± 2) °C for (120 ± 10) min, shaking every

6)
Tinfoil (RM-27) may be obtained from the Society of Automotive Engineers (SAE),, 400 Commonwealth Drive,
Warrendale, PaPA 15096, USA. Tinfoil (RM-27) is an example of a suitable product available commercially. This
information is given for the convenience of users of this document and does not constitute an endorsement by ISO of this
product.
15 min to effect solution of the peroxide. Remove the bottle from the oven, do not disturb the stopper, and
cool in air at a temperature of (23 ± 5) °C for 2 h.
Place approximately 1/8 section of a standard SBR cup, as described in Annex A, in the bottom of each of two
test tubes about 22 mm in diameter and 175 mm in length. Add 10 ml of prepared test fluid to each test tube.
Place a metal strip assembly in each tube with the end of the strips resting on the rubber, the solution covering
about one half of the length of the strips, and the end having the cotter pin remaining out of the solution.
Stopper the tubes with corks and store upright for (70 ± 2) h at (23 ± 5) °C. Loosen the stoppers and place the
tubes for (168 ± 2) h in an oven maintained at (70 ± 2) °C.
After the heating period, remove and disassemble the metal strips and examine for gum deposits. Wipe the
strips with a cloth saturated with ethanol (laboratory grade) and examine for pitting or roughening of the
surface. Place the strips in a desiccator containing a desiccant maintained at (23 ± 5) °C for at least 1 h.
Determine the mass of each strip to the nearest 0,1 mg.
Determine the mass change by dividing the difference in mass of each metal strip by the total surface area of
each metal strip measured in square centimetres. Average the measured values of the duplicates. In the event
of a marginal pass on inspection, or of a failure in only one of the duplicates, another set of duplicate test
samples shall be run. Both repeat samples shall meet all the requirements of 6.9 in Table 1.
6.10 Effect on rubber
6.10.1 Test procedures
6.10.1.1 General
For the test procedure according to 6.10.1.1described in 6.10.1.2, use standard SBR cups (follow Annex A)
andin accordance with Annex A; for that according to 6.10.1.2,6.10.1.3, use standard EPDM slabstock (in
accordance with Annex D).Annex D. Measure the base diameter and hardness of all cups in accordance with
6.5,6.5, discarding any cup whose diameter differs by more than 0,08 mm.
Determine the mass of the cups in air (m ) to the nearest 1 mg and then determine the apparent mass of the
cup immersed in distilled water at (23 ± ± 5) °C (m ). Quickly dip each specimen in ethanol (laboratory grade)
and then air dry or blot dry with filter paper free of lint and foreign material.
6.10.1.2 At 120 °C — SBR cups
7)
Place two SBR cups in a straight-sided round glass jar having a capacity of approximately 250 ml and inner
dimensions of approximately 125 mm height and 50 mm diameter, and a tinned steel lid.
Add 75 ml of fluid to the jar and heat for (70 ± 2) h at (120 ± 2) °C. Allow the jar to cool at (23 ± 5) °C for 60 min
to 90 min. Remove the cups from the jar, wash quickly with ethanol (laboratory grade) and dry in air. Examine
the cups for disintegration as evidenced by blisters or sloughing.
After removal from the alcohol and drying, place each cup in a separate, tared, stoppered weighing bottle and
determine the mass (m ). Remove each cup from its weighing bottle and determine the apparent mass
7)
Suitable test jars (RM-51) and tinned steel lids (RM-52a) may be obtained from the Society of Automotive Engineers
(SAE),, 400 Commonwealth Drive, Warrendale, PaPA 15096, USA. Test jars (RM 51) and tinned steel lids (RM 52a) are an
example of suitable products available commercially. This information is given for the convenience of users of this
document and does not constitute an endorsement by ISO of these product. products.

immersed in distilled water (m ) to determine water displacement after hot fluid immersion. Measure the
base diameter and hardness of each cup within 15 min after removal from the fluid.
Calculate the volume change, ΔV, as a percentage of the original volume, as follows:shown in Formula (1):
(𝑚𝑚 −𝑚𝑚 )−(𝑚𝑚 −𝑚𝑚 )
3 4 1 2
𝛥𝛥𝛥𝛥 = × 100
(𝑚𝑚 −𝑚𝑚 )
1 2
(1)
where
m is the initial mass, in grams, in air;
m is the apparent initial mass, in grams, in water;
m is the mass, in grams, in air after immersion in test fluid;
m is the apparent mass, in grams, in water after immersion in test fluid.
6.10.1.3 At 120 °C — Standard EPDM slabstock
Place two 25 mm × 25 mm standard test specimens in a straight-sided round glass jar having a capacity of
approximately 250 ml and inner dimensions of approximately 125 mm in height and 50 mm in diameter and
a tinned steel lid. Add 75 ml of fluid to the jar and heat for (70 ± 2) h at (120 ± 2) °C before allowing the jar to
cool to (23 ± 5) °C for 60 min to 90 min. Remove the specimens from the jar, wash quickly with ethanol
(laboratory grade) and air dry. Examine the specimens for disintegration as evidenced by blisters or sloughing.
Determine the volume change in accordance with 6.10.1.16.10.1.2 and measure the hardness of each
specimen.
6.10.2 Repeatability (single analyst)
The standard deviation of results (each the average of duplicate determinations) obtained by the same analyst
on different days shall not be greater than 0,05 mm at 46 degrees of freedom. Two such values shall be
considered unacceptable if they differ by more than 0,13 mm (95 % confidence level).
6.10.3 Reproducibility (multi-laboratory)
The standard deviation of results (each the average of duplicates) obtained by analysts in different
laboratories shall not be greater than 0,08 mm at 7 degrees of freedom. Two such values shall be considered
unacceptable if they differ by more than 0,20 mm (95 % confidence level).
6.11 Reserve alkalinity according toin accordance with ASTM D 1121
Procedures shall be as described in ASTM D 1121.
6.12 Resistance to friction-induced noise
Determine s
...