ASTM D4684-20a

Standard Test Method for Determination of Yield Stress and Apparent Viscosity of Engine Oils at Low Temperature

SIGNIFICANCE AND USE
5.1 When an engine oil is cooled, the rate and duration of cooling can affect its yield stress and viscosity. In this laboratory test, a fresh engine oil is slowly cooled through a temperature range where wax crystallization is known to occur, followed by relatively rapid cooling to the final test temperature. These laboratory test results have predicted as failures the known engine oils that have failed in the field because of lack of oil pumpability.4 These documented field failing oils all consisted of oils normally tested at –25 °C. These field failures are believed to be the result of the oil forming a gel structure that results in either excessive yield stress or viscosity of the engine oil, or both.  
5.2 Cooling Profiles:  
5.2.1 For oils to be tested at −20 °C or colder, Table X1.1 applies. The cooling profile described in Table X1.1 is based on the viscosity properties of the ASTM Pumpability Reference Oils (PRO). This series of oils includes oils with normal low-temperature flow properties and oils that have been associated with low-temperature pumpability problems (1-5).5 Significance for the −35 °C and −40 °C temperature profiles is based on the data collected from the “Cold Starting and Pumpability Studies in Modern Engines” conducted by ASTM  (6, 7).  
5.2.2 For oils to be tested at −15 °C or −10 °C, Table X1.2 applies. No significance has been determined for this temperature profile because of the absence of appropriate reference oils. Similarly, precision of the test method using this profile for the −10 °C test temperature is unknown. The temperature profile of Table X1.2 is derived from the one in Table X1.1 and has been moved up in temperature, relative to Table X1.1, in consideration of the expected higher cloud points of the viscous oils tested at −15 °C and −10 °C.
SCOPE
1.1 This test method covers the measurement of the yield stress and viscosity of engine oils after cooling at controlled rates over a period exceeding 45 h to a final test temperature between –10 °C and –40 °C. The precision is stated for test temperatures from –40 °C to –15 °C. The viscosity measurements are made at a shear stress of 525 Pa over a shear rate of 0.4 s–1 to 15 s–1. The viscosity as measured at this shear stress was found to produce the best correlation between the temperature at which the viscosity reached a critical value and borderline pumping failure temperature in engines.  
1.2 This test method contain two procedures: Procedure A incorporates several equipment and procedural modifications from Test Method D4684–02 that have shown to improve the precision of the test, while Procedure B is unchanged from Test Method D4684–02. Additionally, Procedure A applies to those instruments that utilize thermoelectric cooling technology or direct refrigeration technology of recent manufacture for instrument temperature control. Procedure B can use the same instruments used in Procedure A or those cooled by circulating methanol.  
1.3 Procedure A of this test method has precision stated for a yield range from less than 35 Pa to 210 Pa and apparent viscosity range from 4300 mPa·s to 270 000 mPa·s. The test procedure can determine higher yield stress and viscosity levels.  
1.4 This test method is applicable for unused oils, sometimes referred to as fresh oils, designed for both light duty and heavy duty engine applications. It also has been shown to be suitable for used diesel and gasoline engine oils. The applicability to petroleum products other than engine oils has not been determined.  
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5.1 Exception—This test method uses the SI based unit of milliPascal second (mPa·s) for viscosity which is equivalent to, centiPoise (cP).  
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility...

General Information

• Status: Published
• Publication Date: 31-Oct-2020
• ICS: 75.100 - Lubricants, industrial oils and related products
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.07 - Flow Properties

Relations

• Refers: ASTM D3829-18 - Standard Test Method for Predicting the Borderline Pumping Temperature of Engine Oil
• Effective Date: 01-Jun-2018
• Refers: ASTM D3829-17 - Standard Test Method for Predicting the Borderline Pumping Temperature of Engine Oil
• Effective Date: 01-May-2017
• Refers: ASTM D3829-14 - Standard Test Method for Predicting the Borderline Pumping Temperature of Engine Oil
• Effective Date: 01-Jul-2014
• Refers: ASTM D3829-12 - Standard Test Method for Predicting the Borderline Pumping Temperature of Engine Oil
• Effective Date: 01-Nov-2012
• Refers: ASTM E563-11 - Standard Practice for Preparation and Use of an Ice-Point Bath as a Reference Temperature
• Effective Date: 01-May-2011
• Refers: ASTM E563-08 - Standard Practice for Preparation and Use of an Ice-Point Bath as a Reference Temperature
• Effective Date: 01-Nov-2008
• Refers: ASTM D3829-02(2007) - Standard Test Method for Predicting the Borderline Pumping Temperature of Engine Oil
• Effective Date: 01-Nov-2007
• Refers: ASTM D3829-02 - Standard Test Method for Predicting the Borderline Pumping Temperature of Engine Oil
• Effective Date: 10-Nov-2002
• Refers: ASTM E563-02e1 - Standard Practice for Preparation and Use of an Ice-Point Bath as a Reference Temperature
• Effective Date: 10-Oct-2002
• Refers: ASTM E563-02 - Standard Practice for Preparation and Use of an Ice-Point Bath as a Reference Temperature
• Effective Date: 10-Oct-2002

Overview

ASTM D4684-20a: Standard Test Method for Determination of Yield Stress and Apparent Viscosity of Engine Oils at Low Temperature is a critical standard developed by ASTM International. It establishes procedures for measuring the yield stress and apparent viscosity of engine oils after prolonged, controlled-rate cooling to temperatures between –10 °C and –40 °C. These properties are essential for evaluating the low-temperature pumpability of engine oils, helping predict lubricant performance in real-world cold-start conditions.

By following this test method, laboratories and manufacturers can assess the risk of engine oils forming wax gels or exhibiting excessive viscosity at low temperatures-two main contributors to oil pumpability failures in the field. The results obtained inform both product development and quality control, ensuring suitable engine lubrication even under severe winter climates.

Key Topics

• Yield Stress Measurement: Identifies the minimal shear stress needed to initiate flow in cooled engine oils. High yield stress at low temperatures may indicate gel formation and pumpability issues.
• Apparent Viscosity Determination: Measures oil resistance to flow over a specific range of shear rates at low temperatures. Excessively high viscosity can prevent oil circulation during engine startup.
• Cooling Profiles: Addresses how controlled temperature reduction and holding periods impact oil properties, with defined profiles for a range of subzero test temperatures. Advanced reference oils and profiles improve correlation to real-world performance.
• Applicability: Suitable for light-duty and heavy-duty engine oils, both unused (fresh) and used (from engines). The method's compatibility with petroleum products other than engine oils has not been established.
• Procedures: Two procedures are provided:
  • Procedure A: Incorporates enhanced equipment and procedural modifications to boost precision; applicable to modern instruments with thermoelectric or direct refrigeration cooling.
  • Procedure B: Retains prior methods compatible with both updated and older methanol-cooled instruments.

Applications

ASTM D4684-20a is widely used by:

• Engine oil manufacturers for formulation development, to ensure oils maintain adequate flow at low temperatures and prevent field failures.
• Quality assurance laboratories to verify product consistency and compliance with cold-temperature performance specifications.
• Automotive industry to select engine lubricants suited for cold climates and minimize the risk of cold-start lubrication failures.
• Research and development for benchmarking new formulations or studying the impact of additives and base oils on low-temperature rheological properties.
• Regulatory compliance as several industry and manufacturer oil specifications reference this test method to guarantee lubricant pumpability.

Related Standards

ASTM D4684-20a references and aligns with several other international and ASTM standards for consistency and technical accuracy, including:

• ASTM D3829 – Predicting the borderline pumping temperature of engine oil.
• ASTM D8278 – Specification for digital contact thermometers used in flow measurements.
• ASTM E563, E644, E1137, E2877 – Practices and specifications for temperature measurement and thermometer calibration.
• ISO 17025 – General requirements for the competence of testing and calibration laboratories.
• ISO Guide 34 – Requirements for the competence of reference material producers.

By providing a standardized approach to evaluating low-temperature yield stress and apparent viscosity, ASTM D4684-20a ensures reliable, comparable results across laboratories, supporting both product performance claims and industry safety in cold-weather operations.

Keywords: ASTM D4684-20a, engine oil viscosity, yield stress, low temperature, oil pumpability, cold-start lubricants, apparent viscosity, ASTM standard test method, automotive oil performance, engine oil testing

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: D4684 − 20a
Standard Test Method for
Determination of Yield Stress and Apparent Viscosity of
Engine Oils at Low Temperature
This standard is issued under the fixed designation D4684; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber 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* 1.5 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
1.1 This test method covers the measurement of the yield
standard.
stress and viscosity of engine oils after cooling at controlled
1.5.1 Exception—This test method uses the SI based unit of
rates over a period exceeding 45h to a final test temperature
milliPascalsecond(mPa·s)forviscositywhichisequivalentto,
between –10°C and –40°C. The precision is stated for test
centiPoise (cP).
temperatures from –40°C to –15°C. The viscosity measure-
1.6 This standard does not purport to address all of the
ments are made at a shear stress of 525Pa over a shear rate of
–1 –1 safety concerns, if any, associated with its use. It is the
0.4s to 15s . The viscosity as measured at this shear stress
responsibility of the user of this standard to establish appro-
was found to produce the best correlation between the tem-
priate safety, health, and environmental practices and deter-
perature at which the viscosity reached a critical value and
mine the applicability of regulatory limitations prior to use.
borderline pumping failure temperature in engines.
1.7 This international standard was developed in accor-
1.2 This test method contain two procedures: Procedure A
dance with internationally recognized principles on standard-
incorporates several equipment and procedural modifications
ization established in the Decision on Principles for the
from Test Method D4684–02 that have shown to improve the
Development of International Standards, Guides and Recom-
precisionofthetest,whileProcedureBisunchangedfromTest
mendations issued by the World Trade Organization Technical
Method D4684–02.Additionally, ProcedureAapplies to those
Barriers to Trade (TBT) Committee.
instruments that utilize thermoelectric cooling technology or
2. Referenced Documents
direct refrigeration technology of recent manufacture for in-
strument temperature control. Procedure B can use the same
2.1 ASTM Standards:
instruments used in ProcedureAor those cooled by circulating
D3829Test Method for Predicting the Borderline Pumping
methanol.
Temperature of Engine Oil
D8278Specification for Digital Contact Thermometers for
1.3 ProcedureAof this test method has precision stated for
Test Methods Measuring Flow Properties of Fuels and
a yield range from less than 35Pa to 210Pa and apparent
Lubricants
viscosity range from 4300mPa·s to 270000mPa·s. The test
E563Practice for Preparation and Use of an Ice-Point Bath
procedure can determine higher yield stress and viscosity
as a Reference Temperature
levels.
2.2 ISO Standard:
1.4 This test method is applicable for unused oils, some- ISO 17025General Requirements for the Competence of
times referred to as fresh oils, designed for both light duty and Testing and Calibration Laboratories
heavy duty engine applications. It also has been shown to be ISO Guide 34General Requirements for the Competence of
suitable for used diesel and gasoline engine oils. The applica- Reference Material Producers
bilitytopetroleumproductsotherthanengineoilshasnotbeen
3. Terminology
determined.
3.1 Definitions:
1 2
This test method is under the jurisdiction of ASTM Committee D02 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Subcommittee D02.07 on Flow Properties. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Nov. 1, 2020. Published November 2020. Originally the ASTM website.
approved in 1987. Last previous edition approved in 2020 as D4684–20. DOI: Available from International Organization for Standardization (ISO), 1 rue de
10.1520/D4684-20A. Varembé, Case postale 56, CH-1211, Geneva 20, Switzerland, http://www.iso.ch.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4684 − 20a
3.1.1 apparent viscosity, n—the determined viscosity ob- 63
γ˙ 5 (3)
tained by use of this test method. t
3.1.2 digital contact thermometer (DCT), n—an electronic
3.2.4 shear stress, n—the motivating force per unit area for
device consisting of a digital display and associated tempera-
fluid flow.
ture sensing probe.
3.2.4.1 Discussion—For the rotary viscometer being de-
3.1.2.1 Discussion—This device consists of a temperature
scribed in 6.1, the rotor surface is the area under shear or the
sensor connected to a measuring instrument; this instrument
sheararea.Forthistestmethod,endeffectsarenotconsidered.
measures the temperature-dependent quantity of the sensor,
computes the temperature from the measured quantity, and
T 5 9.81 M ~R 1R ! 310 (4)
r o t
provides a digital output. This digital output goes to a digital
T
r
displayand/orrecordingdevicethatmaybeinternalorexternal τ 5 310 (5)
2 πR h
r
to the device.
where:
3.1.2.2 Discussion—The devices are often referred to as a
“digitalthermometers,”howeverthetermincludesdevicesthat
T = torque applied to rotor, N·m,
r
sense temperature by means other than being in physical M = applied mass, g,
R = radius of the shaft, mm,
contact with the media.
o
R = radius of the string, mm,
3.1.2.3 Discussion—PET is an acronym for portable elec-
t
τ = shear stress at the rotor surface, Pa, and
tronic thermometers, a subset of digital contact thermometers
h = height of the rotor, mm.
(DCT).
For the dimensions given in 6.1.1,
3.1.3 Newtonian oil or fluid, n—anoilorfluidthatatagiven
temperature exhibits a constant viscosity at all shear rates or
T 5 31.7 M 310 (6)
r
shear stresses.
τ 5 3.5 M (7)
3.1.4 non-Newtonian oil or fluid, n—an oil or fluid that at a
3.2.5 test oil, n—any oil for which the apparent viscosity
given temperature exhibits a viscosity that varies with chang-
and yield stress are to be determined by this test method.
ing shear stress or shear rate.
3.2.6 unused oil, n—an oil which has not been used in an
3.1.5 viscosity, n—the ratio between the applied shear stress
operating engine.
and rate of shear which is sometimes called the coefficient of
3.2.7 used oil, n—anoilwhichhasbeenusedinanoperating
dynamic viscosity and is a measure of the resistance to flow of
the liquid. engine.
3.2.8 yield stress, n—the shear stress required to initiate
3.2 Definitions of Terms Specific to This Standard:
flow.
3.2.1 calibration oils, n—those oils that establish an instru-
ment’s reference framework of apparent viscosity versus
3.2.8.1 Discussion—For all Newtonian fluids and many
speed, from which the apparent viscosities of test oils are
non-Newtonian fluids, the yield stress is zero.An oil can have
determined.
a yield stress that is a function of its low-temperature cooling
3.2.2 cell constant, n—the ratio of the calibration fluid
rate, soak time, and temperature. Yield stress measurement by
viscosity to the time required to complete the first three
thistestmethoddeterminesonlywhetherthetestoilhasayield
measured revolutions of the rotor.
stressofatleast35Pa;ayieldstressbelow35Paisconsidered
to be insignificant for engine oils.
3.2.3 shear rate, n—the velocity gradient in fluid flow.
3.2.3.1 Discussion—For a Newtonian fluid in a concentric
4. Summary of Test Method
cylinder rotary viscometer in which the shear stress is mea-
4.1 Anengineoilsampleisheldat80°Candthencooledat
sured at the inner cylinder surface (such as this apparatus,
a programmed cooling rate to a final test temperature and held
describedin6.1),andignoringanyendeffects,theshearrateis
foraspecifiedtimeperiod.Attheendofthisperiod,aseriesof
given as follows:
increasing low torques are applied to the rotor shaft until
2ΩR
s
γ˙ 5 (1) rotationoccurstodeterminetheyieldstress,ifanyisexhibited.
2 2
R 2 R
s r
A higher torque is then applied to determine the apparent
4πR
s
viscosity of the sample.
5 (2)
2 2
t ~R 2 R !
s r
5. Significance and Use
where:
γ˙ = shear rate at the surface of the rotor in reciprocal 5.1 When an engine oil is cooled, the rate and duration of
−1
seconds, s ,
cooling can affect its yield stress and viscosity. In this
Ω = angular velocity, rad/s,
laboratory test, a fresh engine oil is slowly cooled through a
R = stator radius, mm,
s temperaturerangewherewaxcrystallizationisknowntooccur,
R = rotor radius, mm, and
r followed by relatively rapid cooling to the final test tempera-
t = time in seconds for one revolution of the rotor.
ture.Theselaboratorytestresultshavepredictedasfailuresthe
For the specific apparatus being described in 6.1.1, known engine oils that have failed in the field because of lack
D4684 − 20a
of oil pumpability. These documented field failing oils all contact rotor shaft. The piece has a center bore of 11mm 6
consistedofoilsnormallytestedat–25°C.Thesefieldfailures 1mm.The cap is made in two halves to facilitate placement in
are believed to be the result of the oil forming a gel structure the top of the cell.
that results in either excessive yield stress or viscosity of the 6.1.2.1 Cell caps shall not be used in the direct refrigeration
engine oil, or both. instruments, since such use would block the flow of cold, dry
air into the stators to keep them frost-free.
5.2 Cooling Profiles:
5.2.1 For oils to be tested at−20°C or colder, Table X1.1 6.2 Weights:
applies.ThecoolingprofiledescribedinTableX1.1isbasedon 6.2.1 Yield Stress Measurement—A set of nine disks and a
the viscosity properties of the ASTM Pumpability Reference disk holder, each with a mass of 10g 6 0.1g.
Oils (PRO). This series of oils includes oils with normal 6.2.2 Viscosity Measurement—A mass of 150g 6 1.0g.
low-temperature flow properties and oils that have been
6.3 Temperature Control System—Regulatesthemini-rotary
associated with low-temperature pumpability problems (1-5).
viscometer block temperature in accordance with the tempera-
Significance for the−35°C and −40°C temperature profiles is
ture requirements described in Table X1.1 or Table X1.2.
based on the data collected from the “Cold Starting and
6.3.1 Temperature Profile—The temperature profile is fully
Pumpability Studies in Modern Engines” conducted byASTM
described in Table X1.1 and Table X1.2.
(6, 7).
6.4 Temperature Measuring Device—Use either a DCT
5.2.2 For oils to be tested at−15°C or−10°C, Table X1.2
meeting the requirements described in 6.4.1 or liquid-in-glass
applies. No significance has been determined for this tempera-
thermometers described in 6.4.2. A calibrated DCT or cali-
ture profile because of the absence of appropriate reference
brated low temperature liquid-in-glass thermometer shall be
oils. Similarly, precision of the test method using this profile
used as the thermometer for temperature measurement below
for the−10°C test temperature is unknown. The temperature
25°Cindependentoftheinstrument’stemperaturecontrol,and
profileofTableX1.2isderivedfromtheoneinTableX1.1and
shall be located in the thermowell.
has been moved up in temperature, relative to Table X1.1,in
consideration of the expected higher cloud points of the
NOTE 1—The display device and sensor must be correctly paired.
viscous oils tested at−15°C and−10°C. Incorrect pairing will result in temperature measurement errors and
possibly irreversible damage to the electronics of the display.
6. Apparatus
6.4.1 Digital Contact Thermometer—Use D02-DCT14
listed in Specification D8278. As an alternative to the metal
6.1 Mini-Rotary Viscometer—An apparatus that consists of
sheathed probe noted in Specification D8278, a glass sheathed
oneormoreviscometriccellsinatemperature-controlledblock
DCT probe with a 6mm O.D. is acceptable provided it meets
made of a metallic material with high thermal conductivity.
the other requirements shown for D02-DCT14 in Specification
Each cell contains a calibrated rotor-stator set. The rotor shall
D8278. A DCT display resolution of 0.01C is preferable. If
have a crossbar near the top of the shaft extending in both
thermowell ID is larger than the probe OD, then a metallic
directions far enough to allow the locking pin (6.6) to stop
sleeve must be used to fill the gap between the probe OD and
rotation at successive half turns. Rotation of the rotor is
thermowell ID with a length of 58mm.
achieved by an applied force acting through a string wound
6.4.1.1 The DCT calibration drift shall be checked at least
around the rotor shaft.
annually by either measuring the ice point or against a
6.1.1 The mini-rotary viscometric cell has the following
reference thermometer in a constant temperature bath at the
dimensions:
prescribed immersion depth to ensure compliance with 6.4.1.
Diameter of rotor 17.06 mm ± 0.08 mm
With respect to an ice bath, Practice E563 provides guidance
Length of rotor 20.00 mm ± 0.14 mm
Inside diameter of cell 19.07 mm ± 0.08 mm
on the preparation and use of an ice bath. However for this use
Radius of shaft 3.18 mm ± 0.13 mm
variance from the specific steps, such as water source, is
Radius of string 0.1 mm
permitted provided preparation is consistent. The basis for the
6.1.2 Cell Cap—A cover inserted into the top of the vis-
variance is due to the reference being used to track change in
cometer cell to minimize room air circulation into the cells is
calibration not verification.
required for thermometrically cooled instruments.The cell cap
NOTE 2—When a DCT’s calibration drifts in one direction over several
is a stepped cylinder 38mm 6 1mm in length made of a low
calibration checks, that is, ice point, it may be an indication of deteriora-
thermalconductivitymaterial,forexample,thermoplasticsuch
tion of the DCT.
as acetyl copolymers that have known solvent resistivity and
6.4.2 For liquid-in-glass thermometers, LiG, two are re-
are suitable for use between the temperature ranges of this test
quired.OneLiGshallbeacalibrated76mmpartialimmersion
method. The top half is a minimum of 25mm in diameter and
thermometer with a scale from +5°C to 1 degree less than the
the bottom half is 19mm in diameter with a tolerance
lowest test temperature in 0.2°C subdivisions. This low
consistent with the cell diameter. The tolerance on the bottom
temperatureLiGthermometershallhaveareportofcalibration
half is such that it will easily fit into cell but not allow cap to
showing the temperature deviation at each calibrated test
temperature. The second LiG thermometer shall be a 76mm
partial immersion thermometer graduated from at least +70°C
Pumpability Reference Oils (PRO) 21 through 29.
to 90°C in 1°C subdivisions, which is used to verify the
The boldface numbers in parentheses refer to the references at the end of this
standard. preheat temperature.
D4684 − 20a
6.4.2.1 Calibration Check—Verify the low temperature Procedure A (TE Cooled and Direct Refrigeration
thermometer at least annually against a reference thermometer Instruments)
inaconstant temperaturebathoranicebath.Thethermometer
istobeinsertedtoitsimmersiondepth.Ifusinganicebath,the 9. Calibration and Standardization
ice point reading is to be taken within 60min after the
9.1 Temperature Control Calibration Procedure—Calibrate
thermometer has been at test temperature for at least 3min. If
the MRV temperature control by comparing the instrument’s
the corrected temperature reading deviates from the reference
displayed temperature against a thermometer in the thermow-
thermometer or the ice point then repeat this calibration check.
ell. The thermometer used shall meet the requirements in 6.4.
If the thermometer deviates from the reference value on two
9.1.1 Place 10mL of a typical test fluid and rotor in each
successive checks then a full thermometer recalibration is
cell.Ifrequired,placecellcapsovereachcellthenplacecover
needed.
on instrument. Cell caps shall not be used on direct refrigera-
6.4.2.2 Recalibration—A complete recalibration of the
tion instruments (see 6.1.2).
liquid-in-glass thermometer, while permitted, is not necessary
9.1.2 Place the thermometer in the thermowell. See Note 3.
in order to meet the accuracy ascribed to liquid-in-glass
Thisthermowellistobeusedforalltemperaturemeasurements
thermometer’s design until the thermometers corrected mea-
below 25°C.
sured temperature deviates from the reference thermometer or
NOTE 3—Prior to inserting the thermometer or DCT probe in the
ice point by one scale division, or until five years has elapsed
thermowell, place several drops (~3) of a heat transfer fluid such as 50/50
since the last full calibration.
water/ethylene glycol mix, CCS reference oil CL100 or a dewaxed low
viscosity mineral oil in the thermowell.
6.5 Supply of Dry Gas—A supply of dry filtered dry gas to
minimize moisture condensation on the upper portions of the
9.1.3 Make these temperature measurements at 80°C then
instrument.
at least three measurements that are 5°C apart from –5°C to
6.5.1 For thermoelectric cooled instruments, which use cell the lowest test temperature used, including both end points to
caps,thedrygassupplyisconnectedtothehousingcover.The
establish a calibration curve for this combination of thermom-
supply of dry gas is discontinued when the cover is removed eter and the instrument’s temperature control. Make at least
for the measurement phase of the test.
two temperature measurements at every calibration tempera-
ture with at least 10 min between observations.
6.6 Locking Pin—A device to keep the rotor from turning
prematurely and able to stop the rotor at the nearest half NOTE 4—All temperatures in this test method refer to the actual
temperature and not necessarily the indicated temperature.
revolution by interaction with the rotor crossbar.
9.1.4 Follow the instrument manufacturers instructions for
7. Reagents and Materials
correcting the instrument’s measured temperature. Alterna-
tivelyestablishacorrectionequationbetweenthermometerand
7.1 Low Cloud-point Newtonian Oil—Calibration oil of
the instruments’s measured temperature then adjust each tem-
approximately 30Pa·s viscosity at –20°C for Procedure B or
perature of the cooling program by the offset determined with
60Pa·s at –25°C for Procedure A for calibration of the
the correction equation.
viscometric cells. The calibration oil shall be obtained from
suppliers complying with ISO Guide 34 and ISO 17025 with
9.2 Viscometer Cell Calibration—The calibration constant
traceability to a national metrology institute (NMI).
of each rotor/stator combination is determined by conducting
two tests at –25°C using a viscometric standard as a test
7.2 Methanol—Commercial or technical grade of dry
sample.
methanol is suitable for the refrigerated cooling bath required
9.2.1 Each cell shall be calibrated twice and the resulting
for some units. (Warning—Flammable.)
calibration constant is to be calculated from the average of the
7.3 Oil Solvent—Commercial heptanes or similar solvent
two determinations of the time for three revolutions of the
that evaporates without leaving a residue is suitable.
rotor. When the two cell calibrations are consecutive, the
(Warning—Flammable.)
second test shall be on a new sample of standard with cleaning
between the steps.
7.4 Acetone—A technical grade of acetone is suitable pro-
vided it does not leave a residue upon evaporation.
NOTE 5—Once a set of rotors has been calibrated in an instrument,
(Warning—Flammable.) subsequent calibration checks can be single determinations if the criteria
of 9.11 are met.
8. Sampling
9.2.2 Use the same 150g mass for both calibration and
viscosity measurements. However, different units may be used
8.1 Arepresentative sample of test oil free from suspended
for calibration and viscosity measurements provided they are
solid material and water is necessary to obtain valid viscosity
certified to be 150g 6 0.1g.
measurements. If the sample in its container is received below
the dew-point temperature of the room, allow the sample to 9.3 Following steps in 10.1, prepare the cells for calibration
warm to room temperature before opening the container. using the calibration oil as the sample.
D4684 − 20a
a full set of samples to run, fill each of the unused cells with a typical test
9.4 Use either the calibration temperature profile for the
sample.
instrument or, alternatively, the cooling profile given in Test
Method D3829 for a –25°C test temperature, and follow the
10.1.3 Repeat 10.1.2 until all test samples are in their cells.
owner’s manual instructions for the instrument to initiate the
NOTE8—Beforeinsertingtherotorsinthecells,inspecteachrotortobe
cooling profile program.
surethattheshaftisstraight,thattherotorsurfaceissmoothandfreefrom
NOTE 6—The use of the calibration temperature profile makes it
dents, scratches, and other imperfections. For rotors with a bearing point
possible to complete two cell constant determinations in one day.
at the bottom of the shaft, ensure that the point is sharp and centered on
the rotor shaft. If these conditions are not met, repair or replace the rotor.
9.5 Place the thermometer in the thermometer well at least
30min prior to executing 9.7. See Note 3. This thermowell 10.1.4 Place each rotor in its cell, and place upper pivot pin
location is to be used for calibration and temperature monitor- in position, including those for any unused cells.
ing during the test procedure.
10.1.5 When use is required, install a cell cap on all cells,
including any unused cells.
9.6 At the completion of the temperature profile for cell
10.1.6 Foreachcell,exceptanyunusedones,placealoopof
calibration, check that the final test temperature is within
the nominal 700mm long string over the crossbar. Hang the
0.1°C of the desired calibration temperature. Final test tem-
string over the timing wheel with a small weight attached such
perature is to be verified independently of the instrument’s
as a large paper clip.Wind the string around the shaft until the
temperature control with a thermometer that has been in the
end is about 100mm below the wheel. Do not overlap
thermometer well for at least the time prescribed in 9.5. See
windings.
Note 3.
NOTE 9—The strings can be pre-wound around the shafts before they
9.7 Beginning with the cell farthest to the left facing the
are installed in 10.1.4.
instrument,follow10.6.3andrecordtherotationtimeforthree
10.1.6.1 Engage the locking pin to prevent the rotor from
revolutions.
turning.
9.8 Repeat 9.7 for each of the remaining cells in numerical
10.1.6.2 Laytheremainingstringoverthetopofthebearing
order.
plate letting it hang over the back of the plate.
9.9 Repeat 9.3 – 9.8 for a second set of calibration data.
10.1.6.3 Repeat10.1.6–10.1.6.2untilallcellswithsamples
to be measured are prepared.
9.10 For each cell (rotor/stator combination) calculate the
10.1.7 Place the housing cover over the viscometric cells.
calibration constant using Eq 8 and 9.
10.1.8 Connect the dry gas supply to the housing cover, as
t 5 ~t 1t !/2 (8)
1 2
noted in 6.5. Set the dry gas flow to approximately 1L⁄h.
C 5η/t (9)
Increase or decrease the flow as necessary to minimize frost or
moisture condensation around the cells.
where:
η = viscosity of the standard oil, mPa·s at test temperature, 10.2 Select the cooling profile for the desired test tempera-
C = cell constant with a 150g mass, mPa, ture and follow the instrument instructions to initiate the
t = time of three rotor revolutions for first calibration,
program. Table X1.3 lists the nominal times to reach a
t = time of three rotor revolutions for second calibration,
2 particular test temperature.
and
10.3 Place the thermometer in the thermowell at least
t = average time of three rotor revolutions.
30min prior to completion of the cooling profile (see Note 3).
9.11 After the calibration constants have been determined,
The same thermowell location is to be used for all measure-
check to see if any cell has a calibration constant differing by
mentsandmustbethesameoneaswasusedinthecalibration.
more than 4% from the average of all cells or if the difference
10.4 At the completion of the cooling profile, check the
between t and t foranycellisgreaterthan4%oftheaverage
1 2
time-temperature plot for the run to ensure that the time-
of t and t . If so, then one or both of the results should be
1 2
temperature profile is within tolerance and that the test tem-
considered suspect. If these criteria are not met, examine the
perature as measured in the thermowell is within 60.2°C of
indicated rotor for damage, repair or replacement as necessary,
the final test temperature. Both of these checks may be done
and repeat the cell calibrations.
automatically by the control software incorporated in some
9.12 If corrected values for the controller temperature and
instruments. Final test temperature is to be verified indepen-
thermometerdeviatebymorethanthetolerance(60.1°C),use
dently from the instrument’s temperature control using a
the procedure in X2.1 to assist in determining the cause and
thermometerthathasbeeninthethermowellforatleast30min
correction.
prior to reaching the test temperature. See Note 3. If the final
test temperature is more than 0.1°C from the set point on two
10. Yield Stress and Viscosity Measurement Procedure
consecutiveruns,theinstrument’stemperaturecontrolmustbe
recalibrated according to 9.1.
10.1 Viscometric Cell Preparation:
10.1.1 If the cells are not clean, clean according to 10.7.
10.5 If the temperature profile is within tolerance, proceed
10.1.2 Place 10mL 6 0.2mL of a test oil sample into a
with measurements. If not, then abort the test and recalibrate
clean cell.
temperature controller as in 9.1.
NOTE7—Allcellsshouldcontainafluidandrotor;iftherearelessthan 10.6 Measurement of the Yield Stress:
D4684 − 20a
10.6.1 Immediately prior to starting measurements, take the 10.6.3.4 Stop the timer after three revolutions of the rotor
cell housing cover off the instrument. from point of release. When the time for one revolution is
greater than 60s, time only one revolution.
10.6.2 Yield Stress Determination—Starting with the cell
farthest to the left while facing the instrument, use the
NOTE 12—The timing of three revolutions may be done automatically.
followingprocedureforeachcellinturn,bypassingtheunused
10.6.3.5 After completing three revolutions (one revolution
cells.
ifthetimeforitisgreaterthan60s),removemassfromstring.
10.6.2.1 Align the pulley wheel with the rotor shaft of the
10.6.3.6 Recordboththetimeandthenumberofrevolutions
cell to be tested.
timed.
10.6.2.2 Hangthestringoverthetimingwheelsuchthatthe
10.6.3.7 If no rotation occurs with the application of the
string hangs past the front of the housing. Make sure that the
150g mass, record the result for that sample as being “Too
disk holder clears the edge of the bench during testing.
Viscous To Measure” (TVTM).
10.6.2.3 Suspend the disk holder from the string.
10.6.3.8 Repeat 10.6.2 – 10.6.3.7 for the remaining cells to
10.6.2.4 Forinstrumentswithautomatictiming,starttiming
be measured.
and then release the locking pin. For manual timing, start
timing immediately after the locking pin is disengaged.
10.7 Cleaning:
10.6.2.5 Observe whether the end of the crossbar moves
10.7.1 Whenallmeasurementshavebeencompleted,setthe
morethan3mmin15s.(This3mmisapproximatelytwicethe
instrument to warm to room temperature or somewhat above.
diameterofthecrossbar.)Analternativeprocedureistheuseof
Cleaning cells above a temperature of 55°C is not recom-
a marked rotation of the timing wheel equivalent to a rotor
mended.
shaft rotation of 3mm.
10.7.2 When the desired cleaning temperature is reached:
10.6.2.6 Electronicortimingwheelmotion-sensingdevices,
10.7.2.1 For instruments with non-removable cells, remove
which are available on some instruments, are suitable alterna-
strings, rotors, and cell caps, when used, then proceed with
tives to direct observation.
10.7.3.
10.6.2.7 If rotor movement of more than 3 mm, or
10.7.2.2 Forinstrumentswithremovablecells,eitherfollow
alternative, in 15s is observed in 10.6.2.5, remove the disk
instructions for non-removable or remove cells from instru-
holder from the end of the string, and proceed to 10.6.3.
ment. The removable cells are to be cleaned by generally
10.6.2.8 If a rotor movement of less than 3mm in 15s is
following the instructions in 10.7.3.
observed in 10.6.2.5, stop timing and lift the disk holder so it
10.7.3 Cleaning Cells:
isnotsupportedbythestring.Thenaddanadditional10gdisk
10.7.3.1 After all of the measurements have been
to disk holder.
completed, exit the cooling program and turn on the heater to
NOTE 10—As additional disks are added to the disk holder, it is warm the viscometric cells to room temperature or somewhat
necessary to suspend the holder with the additional disks from the string
higher. The temperature shall not exceed 50°C.
and restart timing without the use of the locking pin for the remainder of
10.7.3.2 Remove the upper rotor pivots and the rotors.
the yield stress assessment. When using software available for some
10.7.3.3 With vacuum, remove samples, then using an
instruments, ensure that the mass applied is the mass requested by the
program.
appropriate solvent, rinse the cells at least three times with
approximately 15mL of an appropriate solvent for each rinse.
10.6.2.9 Carefully and gently, suspend the disk holder from
Then rinse once with acetone.
the string and start timing.
10.7.3.4 Remove traces of residual solvent by flushing cell
10.6.2.10 Repeat steps in 10.6.2.8 and 10.6.2.9 until the
with dry air or preferably with a vacuum hose to prevent
accumulated mass causes rotation of the rotor. At this point,
contamination with house air. (Warning—When flushing cells
remove the disk holder from the string.
withair,besurethattheairiscleanandfreefromoil,waterand
10.6.2.11 If no rotation is observed with a total of 100g,
other contaminants as these could be left in the cell. House air
recordthattheyieldstressis>350Pa,andproceedwith10.6.3.
is frequently contaminated.)
10.6.3 Measurement of Apparent Viscosity:
10.7.4 Clean rotors with appropriate sample solvent, and
10.6.3.1 Gently suspend the 150g mass from the string.
dry.
10.6.3.2 If the applied mass of 150g will move the rotor, as
soon as the cross-arm is clear of the locking pin, reengage the
11. Calculation of Yield Stress and Apparent Viscosity
locking pin. Allow rotation to continue until the cross-arm
contacts the locking pin causing rotation to stop. If no 11.1 Yield stress is given by the following equation:
appreciable rotation occurs, terminate the test and proceed to
Ys 5 3.5 M (10)
10.6.3.7.
where:
NOTE 11—Yield stresses exceeding the stress exerted by 150g have
Ys = yield stress, Pa, and
been encountered.
M = applied mass, g, at which rotation was observed.
10.6.3.3 When using instruments capable of timing rot
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D4684 − 20 D4684 − 20a
Standard Test Method for
Determination of Yield Stress and Apparent Viscosity of
Engine Oils at Low Temperature
This standard is issued under the fixed designation D4684; 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*
1.1 This test method covers the measurement of the yield stress and viscosity of engine oils after cooling at controlled rates over
a period exceeding 45 h to a final test temperature between –10 °C and –40 °C. The precision is stated for test temperatures from
–1 –1
–40 °C to –15 °C. The viscosity measurements are made at a shear stress of 525 Pa over a shear rate of 0.4 s to 15 s . The
viscosity as measured at this shear stress was found to produce the best correlation between the temperature at which the viscosity
reached a critical value and borderline pumping failure temperature in engines.
1.2 This test method contain two procedures: Procedure A incorporates several equipment and procedural modifications from Test
Method D4684–02 that have shown to improve the precision of the test, while Procedure B is unchanged from Test Method
D4684–02. Additionally, Procedure A applies to those instruments that utilize thermoelectric cooling technology or direct
refrigeration technology of recent manufacture for instrument temperature control. Procedure B can use the same instruments used
in Procedure A or those cooled by circulating methanol.
1.3 Procedure A of this test method has precision stated for a yield range from less than 35 Pa to 210 Pa and apparent viscosity
range from 4300 mPa·s to 270 000 mPa·s. The test procedure can determine higher yield stress and viscosity levels.
1.4 This test method is applicable for unused oils, sometimes referred to as fresh oils, designed for both light duty and heavy duty
engine applications. It also has been shown to be suitable for used diesel and gasoline engine oils. The applicability to petroleum
products other than engine oils has not been determined.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5.1 Exception—This test method uses the SI based unit of milliPascal second (mPa·s) for viscosity which is equivalent to,
centiPoise (cP).
1.6 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.
1.7 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.
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.07 on Flow Properties.
Current edition approved June 1, 2020Nov. 1, 2020. Published June 2020November 2020. Originally approved in 1987. Last previous edition approved in 20182020 as
D4684 – 18.D4684 – 20. DOI: 10.1520/D4684-20.10.1520/D4684-20A.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4684 − 20a
2. Referenced Documents
2.1 ASTM Standards:
D3829 Test Method for Predicting the Borderline Pumping Temperature of Engine Oil
D8278 Specification for Digital Contact Thermometers for Test Methods Measuring Flow Properties of Fuels and Lubricants
E563 Practice for Preparation and Use of an Ice-Point Bath as a Reference Temperature
E644 Test Methods for Testing Industrial Resistance Thermometers
E1137 Specification for Industrial Platinum Resistance Thermometers
E2877 Guide for Digital Contact Thermometers
2.2 ISO Standard:
ISO 17025 General Requirements for the Competence of Testing and Calibration Laboratories
ISO Guide 34 General Requirements for the Competence of Reference Material Producers
3. Terminology
3.1 Definitions:
3.1.1 apparent viscosity, n—the determined viscosity obtained by use of this test method.
3.1.2 digital contact thermometer (DCT), n—an electronic device consisting of a digital display and associated temperature
sensing probe.
3.1.2.1 Discussion—
This device consists of a temperature sensor connected to a measuring instrument; this instrument measures the temperature-
dependent quantity of the sensor, computes the temperature from the measured quantity, and provides a digital output. This digital
output goes to a digital display and/or recording device that may be internal or external to the device. These devices are sometimes
referred to as “digital thermometers.”
3.1.2.2 Discussion—
The devices are often referred to as a “digital thermometers,” however the term includes devices that sense temperature by means
other than being in physical contact with the media.
3.1.2.3 Discussion—
PET is an acronym for portable electronic thermometers, a subset of digital contact thermometers (DCT).
3.1.3 Newtonian oil or fluid, n—an oil or fluid that at a given temperature exhibits a constant viscosity at all shear rates or shear
stresses.
3.1.4 non-Newtonian oil or fluid, n—an oil or fluid that at a given temperature exhibits a viscosity that varies with changing shear
stress or shear rate.
3.1.5 viscosity, n—the ratio between the applied shear stress and rate of shear which is sometimes called the coefficient of dynamic
viscosity and is a measure of the resistance to flow of the liquid.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 calibration oils, n—those oils that establish an instrument’s reference framework of apparent viscosity versus speed, from
which the apparent viscosities of test oils are determined.
3.2.2 cell constant, n—the ratio of the calibration fluid viscosity to the time required to complete the first three measured
revolutions of the rotor.
3.2.3 shear rate, n—the velocity gradient in fluid flow.
3.2.3.1 Discussion—
For a Newtonian fluid in a concentric cylinder rotary viscometer in which the shear stress is measured at the inner cylinder surface
(such as this apparatus, described in 6.1), and ignoring any end effects, the shear rate is given as follows:
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from International Organization for Standardization (ISO), 1 rue de Varembé, Case postale 56, CH-1211, Geneva 20, Switzerland, http://www.iso.ch.
D4684 − 20a
2ΩR
s
γ˙ 5 (1)
2 2
R 2 R
s r
4πR
s
5 (2)
2 2
t R 2 R
~ !
s r
where:
−1
γ˙ = shear rate at the surface of the rotor in reciprocal seconds, s ,
Ω = angular velocity, rad/s,
R = stator radius, mm,
s
R = rotor radius, mm, and
r
t = time in seconds for one revolution of the rotor.
For the specific apparatus being described in 6.1.1,
γ˙ 5 (3)
t
3.2.4 shear stress, n—the motivating force per unit area for fluid flow.
3.2.4.1 Discussion—
For the rotary viscometer being described in 6.1, the rotor surface is the area under shear or the shear area. For this test method,
end effects are not considered.
T 5 9.81 M R 1R 310 (4)
~ !
r o t
T
r
τ 5 310 (5)
2 πR h
r
where:
T = torque applied to rotor, N·m,
r
M = applied mass, g,
R = radius of the shaft, mm,
o
R = radius of the string, mm,
t
τ = shear stress at the rotor surface, Pa, and
h = height of the rotor, mm.
For the dimensions given in 6.1.1,
T 5 31.7 M 310 (6)
r
τ 5 3.5 M (7)
3.2.5 test oil, n—any oil for which the apparent viscosity and yield stress are to be determined by this test method.
3.2.6 unused oil, n—an oil which has not been used in an operating engine.
3.2.7 used oil, n—an oil which has been used in an operating engine.
3.2.8 yield stress, n—the shear stress required to initiate flow.
3.2.8.1 Discussion—
For all Newtonian fluids and many non-Newtonian fluids, the yield stress is zero. An oil can have a yield stress that is a function
of its low-temperature cooling rate, soak time, and temperature. Yield stress measurement by this test method determines only
whether the test oil has a yield stress of at least 35 Pa; a yield stress below 35 Pa is considered to be insignificant for engine oils.
4. Summary of Test Method
4.1 An engine oil sample is held at 80 °C and then cooled at a programmed cooling rate to a final test temperature and held for
D4684 − 20a
a specified time period. At the end of this period, a series of increasing low torques are applied to the rotor shaft until rotation
occurs to determine the yield stress, if any is exhibited. A higher torque is then applied to determine the apparent viscosity of the
sample.
5. Significance and Use
5.1 When an engine oil is cooled, the rate and duration of cooling can affect its yield stress and viscosity. In this laboratory test,
a fresh engine oil is slowly cooled through a temperature range where wax crystallization is known to occur, followed by relatively
rapid cooling to the final test temperature. These laboratory test results have predicted as failures the known engine oils that have
failed in the field because of lack of oil pumpability. These documented field failing oils all consisted of oils normally tested at
–25 °C. These field failures are believed to be the result of the oil forming a gel structure that results in either excessive yield stress
or viscosity of the engine oil, or both.
5.2 Cooling Profiles:
5.2.1 For oils to be tested at −20 °C or colder, Table X1.1 applies. The cooling profile described in Table X1.1 is based on the
viscosity properties of the ASTM Pumpability Reference Oils (PRO). This series of oils includes oils with normal low-temperature
flow properties and oils that have been associated with low-temperature pumpability problems (1-5). Significance for the −35 °C
and −40 °C temperature profiles is based on the data collected from the “Cold Starting and Pumpability Studies in Modern
Engines” conducted by ASTM (6, 7).
5.2.2 For oils to be tested at −15 °C or −10 °C, Table X1.2 applies. No significance has been determined for this temperature
profile because of the absence of appropriate reference oils. Similarly, precision of the test method using this profile for the −10 °C
test temperature is unknown. The temperature profile of Table X1.2 is derived from the one in Table X1.1 and has been moved
up in temperature, relative to Table X1.1, in consideration of the expected higher cloud points of the viscous oils tested at −15 °C
and −10 °C.
6. Apparatus
6.1 Mini-Rotary Viscometer—An apparatus that consists of one or more viscometric cells in a temperature-controlled block made
of a metallic material with high thermal conductivity. Each cell contains a calibrated rotor-stator set. The rotor shall have a crossbar
near the top of the shaft extending in both directions far enough to allow the locking pin (6.6) to stop rotation at successive half
turns. Rotation of the rotor is achieved by an applied force acting through a string wound around the rotor shaft.
6.1.1 The mini-rotary viscometric cell has the following dimensions:
Diameter of rotor 17.06 mm ± 0.08 mm
Length of rotor 20.00 mm ± 0.14 mm
Inside diameter of cell 19.07 mm ± 0.08 mm
Radius of shaft 3.18 mm ± 0.13 mm
Radius of string 0.1 mm
6.1.2 Cell Cap—A cover inserted into the top of the viscometer cell to minimize room air circulation into the cells is required for
thermometrically cooled instruments. The cell cap is a stepped cylinder 38 mm 6 1 mm in length made of a low thermal
conductivity material, for example, thermoplastic such as acetyl copolymers that have known solvent resistivity and are suitable
for use between the temperature ranges of this test method. The top half is a minimum of 25 mm in diameter and the bottom half
is 19 mm in diameter with a tolerance consistent with the cell diameter. The tolerance on the bottom half is such that it will easily
fit into cell but not allow cap to contact rotor shaft. The piece has a center bore of 11 mm 6 1 mm. 11 mm 6 1 mm. The cap is
made in two halves to facilitate placement in the top of the cell.
6.1.2.1 Cell caps shall not be used in the direct refrigeration instruments, since such use would block the flow of cold, dry air into
the stators to keep them frost-free.
6.2 Weights:
Pumpability Reference Oils (PRO) 21 through 29.
The boldface numbers in parentheses refer to the references at the end of this standard.
D4684 − 20a
6.2.1 Yield Stress Measurement—A set of nine disks and a disk holder, each with a mass of 10 g 6 0.1 g.
6.2.2 Viscosity Measurement—A mass of 150 g 6 1.0 g.
6.3 Temperature Control System—Regulates the mini-rotary viscometer block temperature in accordance with the temperature
requirements described in Table X1.1 or Table X1.2.
6.3.1 Temperature Profile—The temperature profile is fully described in Table X1.1 and Table X1.2.
6.4 Temperature Measuring Device—Use either a DCT meeting the requirements described in 6.4.1 or liquid-in-glass
thermometers described in 6.4.2. A calibrated DCT or calibrated low temperature liquid-in-glass thermometer shall be used as the
thermometer for temperature measurement below 25 °C independent of the instrument’s temperature control, and shall be located
in the thermowell.
NOTE 1—The display device and sensor must be correctly paired. Incorrect pairing will result in temperature measurement errors and possibly irreversible
damage to the electronics of the display.
6.4.1 Digital Contact Thermometer—Digital contact thermometer requirements:Use D02-DCT14 listed in
Criteria Minimum Requirements
DCT E2877 Class B
Temperature range –45 °C to 100 °C
Display resolution 0.1 °C minimum, preferably 0.01 °C
Sensor type RTD, such as a PRT or thermistor
Sensor, 3 mm O.D. with an sensing element less than 30 mm in length to be used with a thermowell
metal sheathed sleeve, 6 mm O.D. × 58 mm long with a ~3 mm hole in center.
Sensor, 6 mm O.D. with a sensing element less than 12 mm in length
glass sheathed
Display accuracy ±50 mK (±0.05 °C) for combined probe and sensor
Response time less than or equal to 25 s as defined in Specification E1137
Drift less than 50 mK (0.05 °C) per year
Calibration Error less than 50 mK (0.05 °C) over the range of intended use.
Calibration Range –40 °C to 85 °C
Calibration Data 4 data points evenly distributed over the range of –40 °C to –1 °C and included in calibration
report.
Calibration Report From a calibration laboratory with demonstrated competency in temperature calibration which is
traceable to a national calibration laboratory or metrology standards body
Specification D8278. As an alternative to the metal sheathed probe noted in Specification D8278, a glass sheathed DCT probe
with a 6 mm O.D. is acceptable provided it meets the other requirements shown for D02-DCT14 in Specification D8278. A
DCT display resolution of 0.01 C is preferable. If thermowell ID is larger than the probe OD, then a metallic sleeve must be
used to fill the gap between the probe OD and thermowell ID with a length of 58 mm.
NOTE 2—With respect to DCT probe immersion depth, a procedure to determine minimum immersion depth can be found in Guide E2877, Section 5.3,
or Test Methods E644, Section 7.
6.4.1.1 The DCT calibration drift shall be checked at least annually by either measuring the ice point or against a reference
thermometer in a constant temperature bath at the prescribed immersion depth to ensure compliance with 6.4.1. With respect to
an ice bath, Practice E563 provides guidance on the preparation and use of an ice bath. However for this use variance from the
specific steps, such as water source, is permitted provided preparation is consistent. The basis for the variance is due to the
reference being used to track change in calibration not verification.
NOTE 2—When a DCT’s calibration drifts in one direction over several calibration checks, that is, ice point, it may be an indication of deterioration of
the DCT.
6.4.2 For liquid-in-glass thermometers, LiG, two are required. One LiG shall be a calibrated 76 mm partial immersion
thermometer with a scale from +5 °C to 1 degree less than the lowest test temperature in 0.2 °C subdivisions. This low temperature
LiG thermometer shall have a report of calibration showing the temperature deviation at each calibrated test temperature. The
second LiG thermometer shall be a 76 mm partial immersion thermometer graduated from at least +70 °C to 90 °C in 1 °C
subdivisions, which is used to verify the preheat temperature.
D4684 − 20a
6.4.2.1 Calibration Check—Verify the low temperature thermometer at least annually against a reference thermometer in a
constant temperature bath or an ice bath. The thermometer is to be inserted to its immersion depth. If using an ice bath, the ice
point reading is to be taken within 60 min after the thermometer has been at test temperature for at least 3 min. If the corrected
temperature reading deviates from the reference thermometer or the ice point then repeat this calibration check. If the thermometer
deviates from the reference value on two successive checks then a full thermometer recalibration is needed.
6.4.2.2 Recalibration—A complete recalibration of the liquid-in-glass thermometer, while permitted, is not necessary in order to
meet the accuracy ascribed to liquid-in-glass thermometer’s design until the thermometers corrected measured temperature
deviates from the reference thermometer or ice point by one scale division, or until five years has elapsed since the last full
calibration.
6.5 Supply of Dry Gas—A supply of dry filtered dry gas to minimize moisture condensation on the upper portions of the
instrument.
6.5.1 For thermoelectric cooled instruments, which use cell caps, the dry gas supply is connected to the housing cover. The supply
of dry gas is discontinued when the cover is removed for the measurement phase of the test.
6.6 Locking Pin—A device to keep the rotor from turning prematurely and able to stop the rotor at the nearest half revolution by
interaction with the rotor crossbar.
7. Reagents and Materials
7.1 Low Cloud-point Newtonian Oil—Calibration oil of approximately 30 Pa·s viscosity at –20 °C for Procedure B or 60 Pa·s at
–25 °C for Procedure A for calibration of the viscometric cells. The calibration oil shall be obtained from suppliers complying with
ISO Guide 34 and ISO 17025 with traceability to a national metrology institute (NMI).
7.2 Methanol—Commercial or technical grade of dry methanol is suitable for the refrigerated cooling bath required for some units.
(Warning—Flammable.)
7.3 Oil Solvent—Commercial heptanes or similar solvent that evaporates without leaving a residue is suitable. (Warning—
Flammable.)
7.4 Acetone—A technical grade of acetone is suitable provided it does not leave a residue upon evaporation. (Warning—
Flammable.)
8. Sampling
8.1 A representative sample of test oil free from suspended solid material and water is necessary to obtain valid viscosity
measurements. If the sample in its container is received below the dew-point temperature of the room, allow the sample to warm
to room temperature before opening the container.
Procedure A (TE Cooled and Direct Refrigeration Instruments)
9. Calibration and Standardization
9.1 Temperature Control Calibration Procedure—Calibrate the MRV temperature control by comparing the instrument’s
displayed temperature against a thermometer in the thermowell. The thermometer used shall meet the requirements in 6.4.
9.1.1 Place 10 mL of a typical test fluid and rotor in each cell. If required, place cell caps over each cell then place cover on
instrument. Cell caps shall not be used on direct refrigeration instruments (see 6.1.2).
9.1.2 Place the thermometer in the thermowell. See Note 43. This thermowell is to be used for all temperature measurements
below 25 °C.
NOTE 3—Prior to inserting the thermometer or DCT probe in the thermowell, place several drops (~3) of a heat transfer fluid such as 50/50 water/ethylene
D4684 − 20a
glycol mix, CCS reference oil CL100 or a dewaxed low viscosity mineral oil in the thermowell.
9.1.3 Make these temperature measurements at 80 °C then at least three measurements that are 5 °C apart from –5 °C to the lowest
test temperature used, including both end points to establish a calibration curve for this combination of thermometer and the
instrument’s temperature control. Make at least two temperature measurements at every calibration temperature with at least 10
min between observations.
NOTE 4—All temperatures in this test method refer to the actual temperature and not necessarily the indicated temperature.
9.1.4 Follow the instrument manufacturers instructions for correcting the instrument’s measured temperature. Alternatively
establish a correction equation between thermometer and the instruments’s measured temperature then adjust each temperature of
the cooling program by the offset determined with the correction equation.
9.2 Viscometer Cell Calibration—The calibration constant of each rotor/stator combination is determined by conducting two tests
at –25 °C using a viscometric standard as a test sample.
9.2.1 Each cell shall be calibrated twice and the resulting calibration constant is to be calculated from the average of the two
determinations of the time for three revolutions of the rotor. When the two cell calibrations are consecutive, the second test shall
be on a new sample of standard with cleaning between the steps.
NOTE 5—Once a set of rotors has been calibrated in an instrument, subsequent calibration checks can be single determinations if the criteria of 9.11 are
met.
9.2.2 Use the same 150 g mass for both calibration and viscosity measurements. However, different units may be used for
calibration and viscosity measurements provided they are certified to be 150 g 6 0.1 g.
9.3 Following steps in 10.1, prepare the cells for calibration using the calibration oil as the sample.
9.4 Use either the calibration temperature profile for the instrument or, alternatively, the cooling profile given in Test Method
D3829 for a –25 °C test temperature, and follow the owner’s manual instructions for the instrument to initiate the cooling profile
program.
NOTE 6—The use of the calibration temperature profile makes it possible to complete two cell constant determinations in one day.
9.5 Place the thermometer in the thermometer well at least 30 min prior to executing 9.7. See Note 43. This thermowell location
is to be used for calibration and temperature monitoring during the test procedure.
9.6 At the completion of the temperature profile for cell calibration, check that the final test temperature is within 0.1 °C of the
desired calibration temperature. Final test temperature is to be verified independently of the instrument’s temperature control with
a thermometer that has been in the thermometer well for at least the time prescribed in 9.5. See Note 43.
9.7 Beginning with the cell farthest to the left facing the instrument, follow 10.6.3 and record the rotation time for three
revolutions.
9.8 Repeat 9.7 for each of the remaining cells in numerical order.
9.9 Repeat 9.3 – 9.8 for a second set of calibration data.
9.10 For each cell (rotor/stator combination) calculate the calibration constant using Eq 8 and 9.
t 5 t 1t /2 (8)
~ !
1 2
C 5 η/t (9)
where:
D4684 − 20a
η = viscosity of the standard oil, mPa·s at test temperature,
C = cell constant with a 150 g mass, mPa,
t = time of three rotor revolutions for first calibration,
t = time of three rotor revolutions for second calibration, and
t = average time of three rotor revolutions.
9.11 After the calibration constants have been determined, check to see if any cell has a calibration constant differing by more than
4 % from the average of all cells or if the difference between t and t for any cell is greater than 4 % of the average of t and t .
1 2 1 2
If so, then one or both of the results should be considered suspect. If these criteria are not met, examine the indicated rotor for
damage, repair or replacement as necessary, and repeat the cell calibrations.
9.12 If corrected values for the controller temperature and thermometer deviate by more than the tolerance (60.1 °C), use the
procedure in X2.1 to assist in determining the cause and correction.
10. Yield Stress and Viscosity Measurement Procedure
10.1 Viscometric Cell Preparation:
10.1.1 If the cells are not clean, clean according to 10.7.
10.1.2 Place 10 mL 6 0.2 mL of a test oil sample into a clean cell.
NOTE 7—All cells should contain a fluid and rotor; if there are less than a full set of samples to run, fill each of the unused cells with a typical test sample.
10.1.3 Repeat 10.1.2 until all test samples are in their cells.
NOTE 8—Before inserting the rotors in the cells, inspect each rotor to be sure that the shaft is straight, that the rotor surface is smooth and free from dents,
scratches, and other imperfections. For rotors with a bearing point at the bottom of the shaft, ensure that the point is sharp and centered on the rotor shaft.
If these conditions are not met, repair or replace the rotor.
10.1.4 Place each rotor in its cell, and place upper pivot pin in position, including those for any unused cells.
10.1.5 When use is required, install a cell cap on all cells, including any unused cells.
10.1.6 For each cell, except any unused ones, place a loop of the nominal 700 mm long string over the crossbar. Hang the string
over the timing wheel with a small weight attached such as a large paper clip. Wind the string around the shaft until the end is
about 100 mm below the wheel. Do not overlap windings.
NOTE 9—The strings can be pre-wound around the shafts before they are installed in 10.1.4.
10.1.6.1 Engage the locking pin to prevent the rotor from turning.
10.1.6.2 Lay the remaining string over the top of the bearing plate letting it hang over the back of the plate.
10.1.6.3 Repeat 10.1.6 – 10.1.6.2 until all cells with samples to be measured are prepared.
10.1.7 Place the housing cover over the viscometric cells.
10.1.8 Connect the dry gas supply to the housing cover, as noted in 6.5. Set the dry gas flow to approximately 1 L ⁄h. Increase or
decrease the flow as necessary to minimize frost or moisture condensation around the cells.
10.2 Select the cooling profile for the desired test temperature and follow the instrument instructions to initiate the program. Table
X1.3 lists the nominal times to reach a particular test temperature.
10.3 Place the thermometer in the thermowell at least 30 min prior to completion of the cooling profile (see Note 43). The same
thermowell location is to be used for all measurements and must be the same one as was used in the calibration.
D4684 − 20a
10.4 At the completion of the cooling profile, check the time-temperature plot for the run to ensure that the time-temperature
profile is within tolerance and that the test temperature as measured in the thermowell is within 60.2 °C of the final test
temperature. Both of these checks may be done automatically by the control software incorporated in some instruments. Final test
temperature is to be verified independently from the instrument’s temperature control using a thermometer that has been in the
thermowell for at least 30 min prior to reaching the test temperature. See Note 43. If the final test temperature is more than 0.1 °C
from the set point on two consecutive runs, the instrument’s temperature control must be recalibrated according to 9.1.
10.5 If the temperature profile is within tolerance, proceed with measurements. If not, then abort the test and recalibrate
temperature controller as in 9.1.
10.6 Measurement of the Yield Stress:
10.6.1 Immediately prior to starting measurements, take the cell housing cover off the instrument.
10.6.2 Yield Stress Determination—Starting with the cell farthest to the left while facing the instrument, use the following
procedure for each cell in turn, bypassing the unused cells.
10.6.2.1 Align the pulley wheel with the rotor shaft of the cell to be tested.
10.6.2.2 Hang the string over the timing wheel such that the string hangs past the front of the housing. Make sure that the disk
holder clears the edge of the bench during testing.
10.6.2.3 Suspend the disk holder from the string.
10.6.2.4 For instruments with automatic timing, start timing and then release the locking pin. For manual timing, start timing
immediately after the locking pin is disengaged.
10.6.2.5 Observe whether the end of the crossbar moves more than 3 mm in 15 s. (This 3 mm is approximately twice the diameter
of the crossbar.) An alternative procedure is the use of a marked rotation of the timing wheel equivalent to a rotor shaft rotation
of 3 mm.
10.6.2.6 Electronic or timing wheel motion-sensing devices, which are available on some instruments, are suitable alternatives to
direct observation.
10.6.2.7 If rotor movement of more than 3 mm, or alternative, in 15 s is observed in 10.6.2.5, remove the disk holder from the
end of the string, and proceed to 10.6.3.
10.6.2.8 If a rotor movement of less than 3 mm in 15 s is observed in 10.6.2.5, stop timing and lift the disk holder so it is not
supported by the string. Then add an additional 10 g disk to disk holder.
NOTE 10—As additional disks are added to the disk holder, it is necessary to suspend the holder with the additional disks from the string and restart timing
without the use of the locking pin for the remainder of the yield stress assessment. When using software available for some instruments, ensure that the
mass applied is the mass requested by the program.
10.6.2.9 Carefully and gently, suspend the disk holder from the string and start timing.
10.6.2.10 Repeat steps in 10.6.2.8 and 10.6.2.9 until the accumulated mass causes rotation of the rotor. At this point, remove the
disk holder from the string.
10.6.2.11 If no rotation is observed with a total of 100 g, record that the yield stress is >350 Pa, and proceed with 10.6.3.
10.6.3 Measurement of Apparent Viscosity:
10.6.3.1 Gently suspend the 150 g mass from the string.
10.6.3.2 If the applied mass of 150 g will move the rotor, as soon as the cross-arm is clear of the locking pin, reengage the locking
D4684 − 20a
pin. Allow rotation to continue until the cross-arm contacts the locking pin causing rotation to stop. If no appreciable rotation
occurs, terminate the test and proceed to 10.6.3.7.
NOTE 11—Yield stresses exceeding the stress exerted by 150 g have been encountered.
10.6.3.3 When using instruments capable of timing rotation automatically, initiate viscosity measurement by starting timing, then
release the locking pin. When timing manually, start timing immediately after the locking pin is disengaged.
10.6.3.4 Stop the timer after three revolutions of the rotor from point of release. When the time for one revolution is greater than
60 s, time only one revolution.
NOTE 12—The timing of three revolutions may be done automatically.
10.6.3.5 After completing three revolutions (one revolution if the time for it is greater than 60 s), remove mass from string.
10.6.3.6 Record both the time and the number of revolutions timed.
10.6.3.7 If no rotation occurs with the application of the 150 g mass, record the result for that sample as being “Too Viscous To
Measure” (TVTM).
10.6.3.8 Repeat 10.6.2 – 10.6.3.7 for the remaining cells to be measured.
10.7 Cleaning:
10.7.1 When all measurements have been completed, set the instrument to warm to room temperature or somewhat above.
Cleaning cells above a temperature of 55 °C is not recommended.
10.7.2 When the desired cleaning temperature is reached:
10.7.2.1 For instruments with non-removable cells, remove strings, rotors, and cell caps, when used, then proceed with 10.7.3.
10.7.2.2 For instruments with removable cells, either follow instructions for non-removable or remove cells from instrument. The
removable cells are to be cleaned by generally following the instructions in 10.7.3.
10.7.3 Cleaning Cells:
10.7.3.1 After
...