ASTM D1121-11(2020)

Standard Test Method for Reserve Alkalinity of Engine Coolants and Antirusts

SIGNIFICANCE AND USE
5.1 Reserve alkalinity is the number of millilitres, to the nearest 0.1 mL of 0.100 N hydrochloric acid (HCl) required for the titration to a pH of 5.5 of a 10 mL sample of an undiluted, unused coolant, antirust, or coolant additive, and unused or used solutions thereof.  
5.2 Reserve alkalinity is a term applied to engine coolants and antirusts to indicate the amount of alkaline components present in the product. It is frequently used for quality control during production, and values are often listed in specifications. When applied to used solutions, reserve alkalinity gives an approximate indication of the amount of remaining alkaline components. Unfortunately, the term is sometimes misused in that its numerical value is said to be directly related to coolant quality, the higher the number, the better the coolant. ASTM Committee D15 on Engine Coolants believes there is a need to correct some misconceptions and place the term in its proper perspective.  
5.3 Reserve alkalinity (R.A.) as defined in Section 3 of this method is the number of millilitres of 0.1 N hydrochloric acid required to titrate 10 mL of concentrated coolant to a pH of 5.5. The term is not a completely accurate description of the property being measured because “alkalinity” usually refers to the pH range above 7.0.  
5.4 A review of the origin of the term may be helpful in attempting to understand its proper use. When ethylene glycol was first used as an engine coolant, it was uninhibited. The need for inhibition soon became apparent and triethanolamine was incorporated. When solutions of this inhibited glycol were titrated with dilute hydrochloric acid, it was found that the steepest part of the neutralization curve occurred at a pH of about 5.0. Following the introduction of triethanolamine, other buffers, such as borates and phosphates, have been used. Titration to 5.5 was employed with these buffers which have an end point close to 5.5.  
5.5 Generally, most metals in an automotive cooling...
SCOPE
1.1 This test method covers the determination of the reserve alkalinity of new, unused engine coolants, and liquid antirusts as received, of used or unused aqueous dilutions of the concentrated materials, and of aqueous dilutions of solid antirusts.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Dec-2019
• ICS: 71.100.45 - Refrigerants and antifreezes
• Technical Committee: D15 - Engine Coolants and Related Fluids
• Drafting Committee: D15.04 - Chemical Properties

Relations

• Replaces: ASTM D1121-11 - Standard Test Method for Reserve Alkalinity of Engine Coolants and Antirusts
• Effective Date: 01-Jan-2020
• Refers: ASTM D1287-11(2020) - Standard Test Method for pH of Engine Coolants and Antirusts
• Effective Date: 01-Jan-2020
• Refers: ASTM D1176-14(2019) - Standard Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes
• Effective Date: 01-Oct-2019
• Refers: ASTM D1176-14 - Standard Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes
• Effective Date: 01-Apr-2014
• Refers: ASTM D1287-11 - Standard Test Method for pH of Engine Coolants and Antirusts
• Effective Date: 01-Oct-2011
• Refers: ASTM D1287-09 - Standard Test Method for pH of Engine Coolants and Antirusts
• Effective Date: 01-Nov-2009
• Refers: ASTM D1176-98(2008) - Standard Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes
• Effective Date: 01-Apr-2008
• Refers: ASTM D1123-99(2003)e1 - Standard Test Methods for Water in Engine Coolant Concentrate by the Karl Fischer Reagent Method
• Effective Date: 01-Feb-2007
• Refers: ASTM D1123-99(2003) - Standard Test Methods for Water in Engine Coolant Concentrate by the Karl Fischer Reagent Method
• Effective Date: 10-May-1999
• Refers: ASTM D1176-98(2002) - Standard Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes
• Effective Date: 10-Apr-1998
• Refers: ASTM D1176-98 - Standard Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes
• Effective Date: 10-Apr-1998
• Refers: ASTM D1287-91(2002) - Standard Test Method for pH of Engine Coolants and Antirusts
• Effective Date: 15-Jun-1991
• Refers: ASTM D1287-91(1997)e1 - Standard Test Method for pH of Engine Coolants and Antirusts
• Effective Date: 01-Jan-1991
• Referred By: ASTM D3585-08(2020) - Standard Specification for ASTM Reference Fluid for Coolant Tests
• Effective Date: 01-Jan-2020
• Referred By: ASTM D7518-20 - Standard Specification for 1,3 Propanediol (PDO) Base Engine Coolant for Automobile and Light-Duty Service
• Effective Date: 01-Jan-2020

Overview

ASTM D1121-11(2020), Standard Test Method for Reserve Alkalinity of Engine Coolants and Antirusts, is an internationally recognized method developed by ASTM International for determining the reserve alkalinity of engine coolants and antirust additives. Reserve alkalinity (RA) measures the buffering capacity of coolants and antirust fluids, indicating their ability to neutralize acids generated during engine operation. This standard helps ensure consistent product performance, aids in quality control, and supports compliance with industry specifications.

The method involves titrating a sample of coolant or antirust product with a standard hydrochloric acid solution to a specific pH (5.5), quantifying the volume of acid required to reach this endpoint. The outcome helps manufacturers, laboratories, and automotive professionals evaluate the endurance of protection mechanisms within cooling systems.

Key Topics

• Definition of Reserve Alkalinity: RA is the number of milliliters of 0.100 N hydrochloric acid needed to titrate 10 mL of the product to a pH of 5.5.
• Importance in Engine Coolants: Indicates the level of alkaline buffers (e.g., borates, phosphates) that maintain desirable alkalinity within automotive cooling systems, crucial for corrosion protection.
• Quality Control and Testing: Used throughout coolant production and post-use analysis to monitor potential depletion of protective additives.
• Misconceptions: While RA highlights the presence of alkaline buffers, higher values do not always correlate with better coolant performance or corrosion prevention.
• Test Procedure: Involves accurate sampling, dilution with pure water, use of calibrated pH meter electrodes, and precise titration to the prescribed endpoint.
• Data Interpretation: Depletion of RA during service can be calculated and reported to track coolant efficacy and additive consumption.

Applications

ASTM D1121-11(2020) is widely applied across several industry touchpoints:

• Manufacturing and Formulation: Engine coolant and antirust manufacturers utilize this test method to ensure consistent formulation and to meet required performance specifications for new products.
• Quality Assurance: Production facilities routinely monitor batches of coolant and antirust solutions for proper reserve alkalinity, helping to prevent product failures and warranty claims.
• Automotive and Heavy Equipment Service: Laboratories and automotive service centers use this standard to assess used coolants during engine maintenance, enabling informed decisions on coolant replacement and system health.
• Research and Development: Chemists and engineers apply this method in R&D to optimize coolant formulations for specific operational environments and improve corrosion inhibition with both traditional and new additive technologies.
• Regulatory and Compliance: Organizations reference ASTM D1121-11(2020) in product certifications and supply chain documentation, supporting international trade and adherence to quality standards.

Related Standards

ASTM D1121-11(2020) is frequently used alongside other ASTM standards for engine coolants and related fluids to provide a complete assessment of product quality:

• ASTM D1287 - Test Method for pH of Engine Coolants and Antirusts
• ASTM D1123 - Test Methods for Water in Engine Coolant Concentrate by Karl Fischer Reagent Method
• ASTM D1176 - Practice for Sampling and Preparing Aqueous Solutions of Engine Coolants or Antirusts for Testing Purposes

Referencing these closely linked standards together ensures robust coolant evaluation, from pH and moisture analysis to comprehensive buffering capacity measurements.

Keywords: reserve alkalinity, engine coolant, antirust, ASTM D1121, acid titration, buffer capacity, corrosion protection, coolant additive testing, quality control, automotive cooling systems.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D1121 − 11 (Reapproved 2020)
Standard Test Method for
Reserve Alkalinity of Engine Coolants and Antirusts
This standard is issued under the fixed designation D1121; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope 3.1.1 reserve alkalinity, n—a term applied to engine coolant
concentrates and antirusts to indicate the amount of alkaline
1.1 This test method covers the determination of the reserve
inhibitors present in the product.
alkalinity of new, unused engine coolants, and liquid antirusts
as received, of used or unused aqueous dilutions of the
4. Summary of Test Method
concentrated materials, and of aqueous dilutions of solid
4.1 A 10 mL sample of concentrated coolant, antirust,
antirusts.
coolantadditive,oranaqueousenginecoolantcontainingthese
1.2 The values stated in SI units are to be regarded as
products, is diluted to about 100 mL with water and titrated
standard. No other units of measurement are included in this
potentiometrically with 0.100 N hydrochloric acid to a pH of
standard.
5.5. The volume of acid used is reported to the nearest 0.1 mL.
1.3 This standard does not purport to address all of the
The concentration of coolant or additive in the coolant solution
safety concerns, if any, associated with its use. It is the shall be recorded if required, for calculation of depletion of the
responsibility of the user of this standard to establish appro-
reserve alkalinity during performance tests.
priate safety, health, and environmental practices and deter-
5. Significance and Use
mine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accor- 5.1 Reserve alkalinity is the number of millilitres, to the
dance with internationally recognized principles on standard- nearest 0.1 mLof 0.100 N hydrochloric acid (HCl) required for
ization established in the Decision on Principles for the the titration to a pH of 5.5 of a 10 mL sample of an undiluted,
Development of International Standards, Guides and Recom- unused coolant, antirust, or coolant additive, and unused or
mendations issued by the World Trade Organization Technical used solutions thereof.
Barriers to Trade (TBT) Committee.
5.2 Reserve alkalinity is a term applied to engine coolants
and antirusts to indicate the amount of alkaline components
2. Referenced Documents
present in the product. It is frequently used for quality control
2.1 ASTM Standards: during production, and values are often listed in specifications.
D1123 Test Methods for Water in Engine Coolant Concen- When applied to used solutions, reserve alkalinity gives an
trate by the Karl Fischer Reagent Method
approximate indication of the amount of remaining alkaline
D1176 Practice for Sampling and Preparing Aqueous Solu- components. Unfortunately, the term is sometimes misused in
tions of Engine Coolants orAntirusts forTesting Purposes
that its numerical value is said to be directly related to coolant
D1287 TestMethodforpHofEngineCoolantsandAntirusts quality, the higher the number, the better the coolant. ASTM
Committee D15 on Engine Coolants believes there is a need to
3. Terminology correct some misconceptions and place the term in its proper
perspective.
3.1 Definitions:
5.3 Reserve alkalinity (R.A.) as defined in Section 3 of this
method is the number of millilitres of 0.1 N hydrochloric acid
requiredtotitrate10mLofconcentratedcoolanttoapHof5.5.
This test method is under the jurisdiction ofASTM Committee D15 on Engine
The term is not a completely accurate description of the
Coolants and Related Fluids and is the direct responsibility of Subcommittee
D15.04 on Chemical Properties.
property being measured because “alkalinity” usually refers to
Current edition approved Jan. 1, 2020. Published January 2020. Originally
the pH range above 7.0.
approved in 1950. Last previous edition approved in 2011 as D1121–11. DOI:
10.1520/D1121–11R20.
5.4 A review of the origin of the term may be helpful in
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
attempting to understand its proper use. When ethylene glycol
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
was first used as an engine coolant, it was uninhibited. The
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. need for inhibition soon became apparent and triethanolamine
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1121 − 11 (2020)
was incorporated. When solutions of this inhibited glycol were used, provided it is first ascertained that the reagent is of
titrated with dilute hydrochloric acid, it was found that the sufficiently high purity to permit its use without lessening the
steepest part of the neutralization curve occurred at a pH of accuracy of the determination.
about 5.0. Following the introduction of triethanolamine, other
7.2 Purity of Water—References to water shall be under-
buffers, such as borates and phosphates, have been used.
stood to mean distilled water or water of equal purity. Distilled
Titrationto5.5wasemployedwiththesebufferswhichhavean
water shall be boiled thoroughly, or purged with carbon
end point close to 5.5.
dioxide-free air, to remove carbon dioxide, and shall be
5.5 Generally, most metals in an automotive cooling system protected with a soda-lime tube or the equivalent while cooling
corrode less in solutions which are mildly alkaline. The and in storage. The pH of the water shall be between 6.2 and
commonly used alkaline buffers, borates and phosphates, help 7.2 at 25 °C. Take precautions to prevent contamination of the
to maintain this desirable alkalinity and a stable pH for distilled water with traces of the material used for protection
substantial additions of acid. A well inhibited coolant contains against carbon dioxide.
smaller amounts of other inhibitors (in addition to the buffers), 5
7.3 Standard Buffer Solution —The buffer solutions for
to give broad range corrosion protection for all of the metals
checking pH assemblies and glass electrodes shall be stored in
found in the cooling system. These additional inhibitors may
bottles of chemically resistant glass or polyethylene and shall
contribute very little to the titration, but they can provide
be prepared from salts sold specifically for use, either singly or
excellent corrosion protection.
in combination, as pH standards. The salts shall be dried for 1
5.6 The alkaline inhibitors provide buffering action and h at 110 °C before use.
neutralize acids introduced into the coolant by exhaust gas
7.4 Hydrochloric Acid (0.100 N)—Prepare and standardize
leakage, by residual acid cleaner, or by the oxidation of
0.100 N hydrochloric acid (HCl).
ethylene glycol and propylene glycol. Some inhibitors which
7.5 Phthalate Buffer Solution (0.05 M, pH = 4.01 at
contribute little or no reserve alkalinity may give excellent
25 °C)—Dissolve 10.21 g of potassium hydrogen phthalate in
corrosion protection to certain metals but have little capacity to
distilled water and dilute to 1 L.
combat acid contamination. In view of this, the magnitude of
the R.A. in a coolant is not always a good criterion in 7.6 Phosphate Buffer Solution(0.025 Mwithrespecttoeach
determining its potential protective properties.
phosphate salt, pH = 6.86 at 25 °C)—Dissolve 3.40 g of
potassium dihydrogen phosphate (KH PO ) and 3.55 g of
2 4
5.7 Insummary,theprecautionagainstthemisuseofreserve
anhydrous disodium hydrogen phosphate (Na HPO ) in dis-
2 4
alkalinity is that the reserve alkalinity of an engine coolant
tilled water and dilute to 1 L.
solution is not a dependable measure of its ability to prevent
corrosion, nor can it satisfactorily indicate the additional life of
7.7 Potassium Chloride Electrolyte—Prepare a saturated
the solution. solution of potassium chloride (KCl) in water.
6. Apparatus
8. Sampling
6.1 The pH meter, glass electrode, and calomel electrode,
8.1 Sample the material in accordance with Practice D1176.
shall be as specified in the section onApparatus (Section 5) of
Test Method D1287. 9. Preparation of Electrode System
6.2 It is recognized that many laboratories use a combina- 9.1 Maintenance of Electrodes—Clean the glass electrodes
tion electrode system for measuring the reserve alkalinity of or combination electrode at frequent
...