ASTM D6821-20a

Standard Test Method for Low Temperature Viscosity of Drive Line Lubricants in a Constant Shear Stress Viscometer

SIGNIFICANCE AND USE
5.1 Viscosity of drive line lubricants at low temperature is critical for both gear lubrication and the circulation of the fluid in automatic transmissions. For gear oils (GOs), the issue is whether the fluid characteristics are such that the oil will flow into the channel dug out by the submerged gears as they begin rotating and re-lubricating them as they continue to rotate. For automatic transmission fluids, torque, and tractor fluids the issue is whether the fluid will flow into a pump and through the distribution system rapidly enough for the device to function.  
5.2 The low temperature performance of drive line lubricant flow characteristics was originally evaluated by the channel test. In this test, a pan was filled to a specified depth of approximately 2.5 cm and then cooled to test temperature. The test was performed by scraping a channel through the full depth of the fluid and across the length of the pan after it had soaked at test temperature for a specified time. The time it took the fluid to cover the channel was measured and reported. The channel test was replaced by Test Method D2983 in 1971.  
5.3 The results of this test procedure correlate with the viscometric measurements obtained in Test Method D2983.4 The correlation obtained is:
   where:
  V  =  the apparent viscosity measured by this test method, and   VD2983  =  the apparent viscosity measured by Test Method D2983.    
5.3.1 The equation was obtained by forcing the fit through zero. The coefficient of variation (R2) for this correlation is 0.9948.
SCOPE
1.1 This test method covers the measurement of the viscosity of drive line lubricants (gear oils, automatic transmission fluids, and so forth) with a constant shear stress viscometer at temperatures from –40 °C to 10 °C after a prescribed preheat and controlled cooling to the final test temperature. The precision is stated for test temperatures from –40 °C to –26 °C.  
1.2 The applicability of this particular test method to petroleum products other than drive line lubricants has not been determined.  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3.1 This standard uses the SI based unit of milliPascal second (mPa·s) for viscosity which is equivalent to centiPoise (cP).  
1.4 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.  
1.5 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-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 D2983-23 - Standard Test Method for Low-Temperature Viscosity of Automatic Transmission Fluids, Hydraulic Fluids, and Lubricants using a Rotational Viscometer
• Effective Date: 01-Nov-2023
• Refers: ASTM D6896-18 - Standard Test Method for Determination of Yield Stress and Apparent Viscosity of Used Engine Oils at Low Temperature
• Effective Date: 01-Jun-2018
• 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 D6896-17 - Standard Test Method for Determination of Yield Stress and Apparent Viscosity of Used Engine Oils at Low Temperature
• Effective Date: 01-May-2017
• Refers: ASTM D2983-16 - Standard Test Method for Low-Temperature Viscosity of Automatic Transmission Fluids, Hydraulic Fluids, and Lubricants using a Rotational Viscometer
• Effective Date: 15-Dec-2016
• Refers: ASTM D3829-14 - Standard Test Method for Predicting the Borderline Pumping Temperature of Engine Oil
• Effective Date: 01-Jul-2014
• Refers: ASTM D6896-14 - Standard Test Method for Determination of Yield Stress and Apparent Viscosity of Used Engine Oils at Low Temperature
• 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 D6896-12 - Standard Test Method for Determination of Yield Stress and Apparent Viscosity of Used Engine Oils at Low Temperature
• 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 D6896-03(2007) - Standard Test Method for Determination of Yield Stress and Apparent Viscosity of Used Engine Oils at Low Temperature
• Effective Date: 01-Nov-2007
• Refers: ASTM D2983-04a - Standard Test Method for Low-Temperature Viscosity of Lubricants Measured by Brookfield Viscometer
• Effective Date: 01-May-2004

Overview

ASTM D6821-20a is the Standard Test Method for Low Temperature Viscosity of Drive Line Lubricants in a Constant Shear Stress Viscometer. Developed by ASTM International, this standard outlines a reliable method for measuring the viscosity of drive line lubricants, such as gear oils and automatic transmission fluids, at temperatures ranging from –40 °C to 10 °C. Assessment of low temperature viscosity is essential for ensuring proper functioning of automotive components in cold conditions, supporting gear lubrication and fluid circulation, and enabling product specification and quality control in lubricant manufacturing.

Key Topics

• Low Temperature Viscosity Measurement: The standard specifies procedures for determining the apparent viscosity of drive line lubricants using a constant shear stress viscometer after a precise preheating and controlled cooling protocol.
• Critical Properties: Focus is placed on fluidity at low temperatures, which is crucial for proper gear re-lubrication and timely fluid delivery to transmission and pump systems.
• Test Apparatus: Use of a mini-rotary viscometer with a temperature-controlled environment and calibrated digital contact thermometer (DCT) or liquid-in-glass thermometer is required.
• Precision and Reporting: Results must meet strict repeatability thresholds. The apparent viscosity is measured in milliPascal seconds (mPa·s), and results are reported alongside the final test temperature and, optionally, the yield stress.
• Calibration and Standardization: Each viscometric cell is calibrated with Newtonian reference oils that are traceable to national standards, ensuring consistency and reproducibility.

Applications

ASTM D6821-20a is widely used within the petroleum, automotive, and lubricant manufacturing sectors for:

• Product Development and Quality Assurance: Ensuring that gear oils, automatic transmission fluids, and similar lubricants meet low temperature flow performance criteria necessary for reliable vehicle operation, especially in subzero climates.
• Compliance and Certification: Supporting product claims and compliance with industry requirements for low temperature fluidity.
• Field Failure Analysis: Investigating drive line fluid performance issues related to cold start or low temperature operation in commercial fleets, agricultural machinery, and passenger vehicles.
• Comparative Evaluation: Offering correlated data (via Test Method D2983) for benchmarking lubricant performance across formulations or brands.

Proper low temperature viscosity helps prevent start-up wear, supports effective gear engagement, and reduces the risk of pump starvation-the inability of the fluid to flow rapidly enough to essential components in cold conditions.

Related Standards

Several relevant standards complement ASTM D6821-20a in assessing lubricant performance and thermal properties:

• ASTM D2983: Standard Test Method for Low-Temperature Viscosity of Automatic Transmission Fluids, Hydraulic Fluids, and Lubricants using a Rotational Viscometer.
• ASTM D3829: Test Method for Predicting the Borderline Pumping Temperature of Engine Oil.
• ASTM D4684: Test Method for Determination of Yield Stress and Apparent Viscosity of Engine Oils at Low Temperature.
• ASTM D6896: Test Method for Determination of Yield Stress and Apparent Viscosity of Used Engine Oils at Low Temperature.
• ASTM D8278: Specification for Digital Contact Thermometers for Test Methods Measuring Flow Properties of Fuels and Lubricants.
• ISO 17025: General Requirements for the Competence of Testing and Calibration Laboratories.
• ISO Guide 34: General Requirements for the Competence of Reference Material Producers.

Practical Value

By standardizing the determination of low temperature viscosity in drive line lubricants, ASTM D6821-20a enables manufacturers, laboratories, and regulatory bodies to:

• Maintain consistency in lubricant evaluation.
• Reduce variability in field performance.
• Select and validate lubricants suitable for extreme cold environments.
• Build consumer confidence in lubricant performance and safety.

In summary, adherence to this ASTM standard supports optimal gearbox and transmission operation at low temperatures, reducing equipment downtime and enhancing product reliability across demanding automotive and industrial applications.

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: D6821 − 20a
Standard Test Method for
Low Temperature Viscosity of Drive Line Lubricants in a
Constant Shear Stress Viscometer
This standard is issued under the fixed designation D6821; 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.
1. Scope* cants using a Rotational Viscometer
D3829Test Method for Predicting the Borderline Pumping
1.1 This test method covers the measurement of the viscos-
Temperature of Engine Oil
ity of drive line lubricants (gear oils, automatic transmission
D4684Test Method for Determination of Yield Stress and
fluids, and so forth) with a constant shear stress viscometer at
Apparent Viscosity of Engine Oils at Low Temperature
temperatures from –40°C to 10°C after a prescribed preheat
D6896Test Method for Determination of Yield Stress and
and controlled cooling to the final test temperature. The
ApparentViscosity of Used Engine Oils at LowTempera-
precisionisstatedfortesttemperaturesfrom–40°Cto–26°C.
ture
1.2 The applicability of this particular test method to petro-
D8278Specification for Digital Contact Thermometers for
leum products other than drive line lubricants has not been
Test Methods Measuring Flow Properties of Fuels and
determined.
Lubricants
E563Practice for Preparation and Use of an Ice-Point Bath
1.3 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this as a Reference Temperature
2.2 ISO Standards:
standard.
1.3.1 This standard uses the SI based unit of milliPascal ISO 17025General Requirements for the Competence of
Testing and Calibration Laboratories
second (mPa·s) for viscosity which is equivalent to centiPoise
(cP). ISO Guide 34General Requirements for the Competence of
Reference Material Producers
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Terminology
responsibility of the user of this standard to establish appro-
3.1 Definitions:
priate safety, health, and environmental practices and deter-
3.1.1 apparent viscosity, n—the determined viscosity ob-
mine the applicability of regulatory limitations prior to use.
tained by the use of this test method.
1.5 This international standard was developed in accor-
3.1.2 digital contact thermometer (DCT), n—an electronic
dance with internationally recognized principles on standard-
device consisting of a digital display and associated tempera-
ization established in the Decision on Principles for the
ture sensing probe.
Development of International Standards, Guides and Recom-
3.1.2.1 Discussion—This device consists of a temperature
mendations issued by the World Trade Organization Technical
sensor connected to a measuring instrument; this instrument
Barriers to Trade (TBT) Committee.
measures the temperature-dependent quantity of the sensor,
2. Referenced Documents
computes the temperature from the measured quantity, and
provides a digital output. This digital output goes to a digital
2.1 ASTM Standards:
displayand/orrecordingdevicethatmaybeinternalorexternal
D2983Test Method for Low-Temperature Viscosity of Au-
to the device.
tomaticTransmissionFluids,HydraulicFluids,andLubri-
3.1.2.2 Discussion—The devices are often referred to as a
“digitalthermometers,”howeverthetermincludesdevicesthat
This test method is under the jurisdiction of ASTM Committee D02 on
sense temperature by means other than being in physical
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
contact with the media.
Subcommittee D02.07 on Flow Properties.
3.1.2.3 Discussion—PET is an acronym for portable elec-
Current edition approved Nov. 1, 2020. Published November 2020. Originally
approved in 2002. Last previous edition approved in 2020 as D6821–20. DOI:
tronic thermometers, a subset of digital contact thermometers
10.1520/D6821-20A.
(DCT).
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 Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.
*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
D6821 − 20a
3.1.3 Newtonian oil or fluid, n—anoilorfluidthatatagiven T 5 32 M 310 (6)
r
temperature exhibits a constant viscosity at all shear rates or
τ 5 4.5 M (7)
shear stresses.
3.2.4 test oil, n—any oil for which the apparent viscosity is
3.1.4 non-Newtonian oil or fluid, n—an oil or fluid that at a
to be determined by this test method.
given temperature exhibits a viscosity that varies with chang-
3.2.5 yield stress, n—the shear stress required to initiate
ing shear stress or shear rate.
flow.
3.1.5 viscosity, n—the ratio between the applied shear stress
3.2.5.1 Discussion—For Newtonian fluids and some non-
and rate of shear which is sometimes called the coefficient of
Newtonian fluids the yield stress is zero. An oil can have a
dynamic viscosity and is a measure of the resistance to flow of
yield stress that is a function of its low-temperature cooling
the liquid.
rate, soak time, and temperature.
3.1.5.1 Discussion—The SI unit of viscosity is the pascal
4. Summary of Test Method
second [Pa·s]. The submultiple unit is millipascal seconds
(mPa·s).
4.1 A drive line fluid is preheated to 50°C for a specified
time and then cooled at a programmed rate (see Table X1.1)to
3.2 Definitions of Terms Specific to This Standard:
the final test temperature and soaked at the final temperature
3.2.1 calibration oils, n—those oils that establish an instru-
foradefinedperiodoftime.Atthecompletionofthesoaktime,
ment’s reference framework of apparent viscosity versus
the viscosity is measured by applying a prescribed torque and
speed, from which the apparent viscosities of test oils are
measuring rotational speed to determine the apparent viscosity
determined.
of the sample.
3.2.2 shear rate, n—the velocity gradient in fluid flow.
3.2.2.1 Discussion—For a Newtonian fluid in a concentric
5. Significance and Use
cylinder rotary viscometer in which the shear stress is mea-
5.1 Viscosity of drive line lubricants at low temperature is
sured at the inner cylinder surface (such as the apparatus
critical for both gear lubrication and the circulation of the fluid
describedin6.1),andignoringanyendeffects,theshearrateis
in automatic transmissions. For gear oils (GOs), the issue is
given as follows:
whether the fluid characteristics are such that the oil will flow
2 Ω R
s
into the channel dug out by the submerged gears as they begin
γ˙ 5 (1)
2 2
R 2 R
s r
rotating and re-lubricating them as they continue to rotate. For
4 π R
automatic transmission fluids, torque, and tractor fluids the
s
γ˙ 5 (2)
2 2
t~R 2 R ! issueiswhetherthefluidwillflowintoapumpandthroughthe
s r
distribution system rapidly enough for the device to function.
where:
5.2 Thelowtemperatureperformanceofdrivelinelubricant
γ˙ = shear rate at the surface of the rotor in reciprocal
-1
flow characteristics was originally evaluated by the channel
seconds, s ,
test. In this test, a pan was filled to a specified depth of
Ω = angular velocity, rad/s,
approximately 2.5 cm and then cooled to test temperature.The
R = stator radius, mm,
s
testwasperformedbyscrapingachannelthroughthefulldepth
R = rotor radius, mm, and
r
t = time for one revolution of the rotor, s.
of the fluid and across the length of the pan after it had soaked
at test temperature for a specified time. The time it took the
For the specific apparatus being described in 6.1.1,
fluid to cover the channel was measured and reported. The
channel test was replaced by Test Method D2983 in 1971.
γ˙ 5 (3)
t
5.3 The results of this test procedure correlate with the
3.2.3 shear stress, n—the motivating force per unit area for
viscometric measurements obtained in Test Method D2983.
fluid flow.
The correlation obtained is:
3.2.3.1 Discussion—For the rotary viscometer being de-
V 5 0.941 3V (8)
D2983
scribed in 6.1, the rotor surface is the area under shear or the
sheararea.Forthistestmethod,endeffectsarenotconsidered.
where:
T 5 9.81 M ~R 1R ! 310 (4) V = the apparent viscosity measured by this test
r o t
method, and
T
r
=
τ 5 310 (5)
V the apparent viscosity measured by Test Method
D2983
2 π R h
r
D2983.
where:
5.3.1 The equation was obtained by forcing the fit through
T = torque applied to rotor, N·m, 2
r
zero. The coefficient of variation (R ) for this correlation is
M = applied mass, g,
0.9948.
R = radius of the shaft, mm,
o
R = radius of the string, mm,
r
τ = shear stress at the rotor surface, Pa, and
SAE Paper 1999–01–3672, “Viscosity of Drive-Line Lubricants by a Special
h = height of the rotor face, mm.
Mini-Rotary Viscometer Technique.” Available from Society of Automotive
For the dimensions given in 6.1.1, Engineers, 400 Commonwealth Dr., Warrendale, PA 15096-0001.
D6821 − 20a
6. Apparatus thermometer with a scale from +5°C to 1 degree lower than
the lowest test temperature in 0.2°C subdivisions. For test
6.1 Mini-Rotary Viscometer—An apparatus that consists of
temperatures less than –35°C, use a liquid-in-glass thermom-
one or more viscometric cells in a temperature controlled
eter with at least a scale range of 2 degrees Celsius in 0.2°C
aluminumblock.Eachcell,whenfittedwiththespecifiedrotor,
subdivisions. The low temperature LiG thermometer(s) shall
becomes a calibrated rotor-stator set. Rotation of the rotor is
have a report of calibration showing the temperature deviation
achieved by an applied load acting through a string wound
at each calibrated test temperature. The second LiG thermom-
around the rotor shaft. The top bearing plate is fitted with
etershallbea76mmpartialimmersionthermometergraduated
locking pins for holding the rotors stationary. Time of rotation
from at least +40°C to 90 °C in 1°C subdivisions, which is
is measured electronically by a device attached to the timing
used to verify the preheat temperature.
wheel.
6.4.2.1 Calibration Check—Verify the low temperature
6.1.1 Themini-rotaryviscometriccellforthisprocedurehas
thermometer at least annually against a reference thermometer
the following typical dimensions:
in a constant temperature bath or in an ice bath.The thermom-
Diameter of rotor 15.00 mm ± 0.08 mm
eter is to be inserted to its immersion depth. If using an ice
Length of rotor 20.00 mm ± 0.14 mm
Inside diameter of cell 19.07 mm ± 0.08 mm
bath,theicepointreadingistobetakenwithin60minafterthe
Radius of shaft 3.18 mm ± 0.13 mm
thermometer has been at test temperature for at least 3 min. If
Radius of string 0.1 mm
the corrected temperature reading deviates from the reference
6.2 Weight—For applying mass. Weights are to be in incre-
thermometer or the ice point then repeat this calibration check.
ments of 2.5 g 6 1%. A minimum of eight weight segments
If the thermometer deviates from the reference value on two
will be needed for the measurements defined in this test
successive checks then a full thermometer recalibration is
method. One segment will be the weight holder.
needed.
6.3 Temperature Control System—That will regulate the
6.4.2.2 Recalibration—A complete recalibration of the
samplesinthecellsaccordingtothecoolingprogramdescribed
liquid-in-glass thermometer, while permitted, is not necessary
in Table X1.1 and within the tolerances specified in the table.
in order to meet the accuracy ascribed to liquid-in-glass
thermometer’s design until the thermometers corrected mea-
6.4 Temperature Measuring Device—Use either a DCT
sured temperature deviates from the reference thermometer or
meeting the requirements described in 6.4.1 or liquid-in-glass
ice point by one scale division, or until five years has elapsed
thermometers described in 6.4.2. A calibrated DCT or cali-
since the last full calibration.
brated low temperature liquid-in-glass thermometer shall be
used as the thermometer for temperature measurement below
6.5 Supply of Dry Gas—A supply of dry filtered gas to
25°Cindependentoftheinstrument’stemperaturecontrol,and
minimize moisture condensation on the upper portions of the
shall be located in the thermowell.
instrument.
6.5.1 For thermoelectric cooled instruments, which use cell
NOTE 1—The DCT display device and sensor must be correctly paired.
Incorrect pairing will result in temperature measurement errors and
caps,thedrygassupplyisconnectedtothehousingcover.The
possibly irreversible damage to the electronics of the display.
supply of dry gas is discontinued when the cover is removed
6.4.1 Digital Contact Thermometer—Use D02-DCT14
for the measurement phase of the test.
listed in Specification D8278. As an alternative to the metal
6.6 Locking Pin—A device to keep the rotor from turning
sheathed probe noted in Specification D8278, a glass sheathed
prematurely and able to stop the rotor at the nearest half
DCT probe with a 6mm O.D. is acceptable provided it meets
revolution by interaction with the rotor crossbar.
the other requirements shown for D02-DCT14 in Specification
D8278. A DCT display resolution of 0.01C is preferable. If
7. Reagents and Materials
thermowell ID is larger than the probe OD, then a metallic
sleeve must be used to fill the gap between the probe OD and 7.1 Low Cloud-point, Newtonian Oil, a calibration oil of
approximately60Pa·sviscosityat−25°Cforcalibrationofthe
thermowell ID with a length of 58mm.
6.4.1.1 The DCT calibration drift shall be checked at least viscometric cells. The calibration oil shall be obtained from
suppliers complying with ISO Guide 34 and ISO 17025 with
annually by either measuring the ice point or against a
reference thermometer in a constant temperature bath at the traceability to a national metrology institute (NMI).
prescribed immersion depth to ensure compliance with 6.4.1.
7.2 Oil Solvent, commercial heptanes or similar solvent for
With respect to an ice bath, Practice E563 provides guidance
the test fluids that evaporates without leaving a residue.
onthepreparationanduseofanicebath.However,forthisuse,
(Warning—Flammable.)
variance from the specific steps, such as water source, is
7.3 Acetone—A technical grade of acetone is suitable pro-
permitted provided preparation is consistent. The basis for the
vided it does not leave a residue upon evaporation.
varianceisduetotheicebathreferencebeingusedfortracking
(Warning—Flammable.)
change in calibration not verification.
NOTE 2—When a DCT’s calibration drifts in one direction over several
8. Sampling
calibration checks, that is, ice point, it may be an indication of deteriora-
tion of the DCT.
8.1 Arepresentative sample of test oil free from suspended
6.4.2 For liquid-in-glass thermometers, LiG, two are re- solid material and water is necessary to obtain valid viscosity
quired.OneLiGshallbeacalibrated76mmpartialimmersion measurements. If the sample in its container is received below
D6821 − 20a
the dew-point temperature of the room, allow the sample to η
o
C 5 (9)
warm to room temperature before opening the container. t
where:
9. Calibration
η = viscosity of the calibration oil, mPa·s at −25°C,
o
9.1 Temperature Control Calibration Procedure—Calibrate
C = cell constant for a 20 g mass, mPa, and
the MRV temperature control by comparing the instrument’s
t = time for three complete rotor revolutions, s.
displayedtemperaturetoathermometerinthethermowell.The
thermometer used shall meet the requirements in 6.4.
10. Procedure
9.1.1 Place 10 mL of a typical test fluid and rotors in each
10.1 Viscometric Cell Preparation:
cell then place cover on instrument. Cell caps maybe used if
10.1.1
...

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: D6821 − 20 D6821 − 20a
Standard Test Method for
Low Temperature Viscosity of Drive Line Lubricants in a
Constant Shear Stress Viscometer
This standard is issued under the fixed designation D6821; 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.
1. Scope*
1.1 This test method covers the measurement of the viscosity of drive line lubricants (gear oils, automatic transmission fluids, and
so forth) with a constant shear stress viscometer at temperatures from –40 °C to 10 °C after a prescribed preheat and controlled
cooling to the final test temperature. The precision is stated for test temperatures from –40 °C to –26 °C.
1.2 The applicability of this particular test method to petroleum products other than drive line lubricants has not been determined.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3.1 This standard uses the SI based unit of milliPascal second (mPa·s) for viscosity which is equivalent to centiPoise (cP).
1.4 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.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
D2983 Test Method for Low-Temperature Viscosity of Automatic Transmission Fluids, Hydraulic Fluids, and Lubricants using
a Rotational Viscometer
D3829 Test Method for Predicting the Borderline Pumping Temperature of Engine Oil
D4684 Test Method for Determination of Yield Stress and Apparent Viscosity of Engine Oils at Low Temperature
D6896 Test Method for Determination of Yield Stress and Apparent Viscosity of Used Engine Oils at Low Temperature
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
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 2002. Last previous edition approved in 20182020 as
D6821 – 18.D6821 – 20. DOI: 10.1520/D6821-20.10.1520/D6821-20A.
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.
*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
D6821 − 20a
2.2 ISO Standards:
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 the 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.
3.1.5.1 Discussion—
The SI unit of viscosity is the pascal second [Pa·s]. The submultiple unit is millipascal seconds (mPa·s).
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 shear rate, n—the velocity gradient in fluid flow.
3.2.2.1 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 the apparatus described in 6.1), and ignoring any end effects, the shear rate is given as follows:
2 Ω R
s
γ˙ 5 (1)
2 2
R 2 R
s r
4 π R
s
γ˙ 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 for one revolution of the rotor, s.
For the specific apparatus being described in 6.1.1,
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
D6821 − 20a
γ˙ 5 (3)
t
3.2.3 shear stress, n—the motivating force per unit area for fluid flow.
3.2.3.1 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 π R 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,
r
τ = shear stress at the rotor surface, Pa, and
h = height of the rotor face, mm.
For the dimensions given in 6.1.1,
T 5 32 M 310 (6)
r
τ 5 4.5 M (7)
3.2.4 test oil, n—any oil for which the apparent viscosity is to be determined by this test method.
3.2.5 yield stress, n—the shear stress required to initiate flow.
3.2.5.1 Discussion—
For Newtonian fluids and some 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.
4. Summary of Test Method
4.1 A drive line fluid is preheated to 50 °C for a specified time and then cooled at a programmed rate (see Table X1.1) to the final
test temperature and soaked at the final temperature for a defined period of time. At the completion of the soak time, the viscosity
is measured by applying a prescribed torque and measuring rotational speed to determine the apparent viscosity of the sample.
5. Significance and Use
5.1 Viscosity of drive line lubricants at low temperature is critical for both gear lubrication and the circulation of the fluid in
automatic transmissions. For gear oils (GOs), the issue is whether the fluid characteristics are such that the oil will flow into the
channel dug out by the submerged gears as they begin rotating and re-lubricating them as they continue to rotate. For automatic
transmission fluids, torque, and tractor fluids the issue is whether the fluid will flow into a pump and through the distribution system
rapidly enough for the device to function.
5.2 The low temperature performance of drive line lubricant flow characteristics was originally evaluated by the channel test. In
this test, a pan was filled to a specified depth of approximately 2.5 cm and then cooled to test temperature. The test was performed
by scraping a channel through the full depth of the fluid and across the length of the pan after it had soaked at test temperature
for a specified time. The time it took the fluid to cover the channel was measured and reported. The channel test was replaced by
Test Method D2983 in 1971.
5.3 The results of this test procedure correlate with the viscometric measurements obtained in Test Method D2983. The
correlation obtained is:
V 5 0.941 3V (8)
D2983
SAE Paper 1999–01–3672, “Viscosity of Drive-Line Lubricants by a Special Mini-Rotary Viscometer Technique.” Available from Society of Automotive Engineers, 400
Commonwealth Dr., Warrendale, PA 15096-0001.
D6821 − 20a
where:
V = the apparent viscosity measured by this test method, and
=
V the apparent viscosity measured by Test Method D2983.
D2983
5.3.1 The equation was obtained by forcing the fit through zero. The coefficient of variation (R ) for this correlation is 0.9948.
6. Apparatus
6.1 Mini-Rotary Viscometer—An apparatus that consists of one or more viscometric cells in a temperature controlled aluminum
block. Each cell, when fitted with the specified rotor, becomes a calibrated rotor-stator set. Rotation of the rotor is achieved by an
applied load acting through a string wound around the rotor shaft. The top bearing plate is fitted with locking pins for holding the
rotors stationary. Time of rotation is measured electronically by a device attached to the timing wheel.
6.1.1 The mini-rotary viscometric cell for this procedure has the following typical dimensions:
Diameter of rotor 15.00 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
6.2 Weight—For applying mass. Weights are to be in increments of 2.5 g 6 1 %. A minimum of eight weight segments will be
needed for the measurements defined in this test method. One segment will be the weight holder.
6.3 Temperature Control System—That will regulate the samples in the cells according to the cooling program described in Table
X1.1 and within the tolerances specified in the table.
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 DCT 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 Requirements: Thermometer—
Criteria Minimum Requirements
DCT Guide 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 sleeve, 6 mm O.D. ×
metal sheathed 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 8 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 na-
tional calibration laboratory or metrology standards body
Use D02-DCT14 listed in 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.
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NOTE 2—With respect to DCT probe immersion depth, a procedure to determine minimum depth can be found in Guide E2877, Section 5.3, or Test
Methods E644, Section 7.
6.4.1.1 The DCT calibration driftshall 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 ice bath reference being used for tracking 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 lower than the lowest test temperature in 0.2 °C subdivisions. For test
temperatures less than –35 °C, use a liquid-in-glass thermometer with at least a scale range of 2 degrees Celsius in 0.2 °C
subdivisions. The low temperature LiG thermometer(s) 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
+40 °C to 90 °C in 1 °C subdivisions, which is used to verify the preheat temperature.
6.4.2.1 Calibration Check—Verify the low temperature thermometer at least annually against a reference thermometer in a
constant temperature bath or in an ice bath. The thermometer is to be insertinserted 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 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, a calibration oil of approximately 60 Pa·s viscosity at −25 °C 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 Oil Solvent, commercial heptanes or similar solvent for the test fluids that evaporates without leaving a residue.
(Warning—Flammable.)
7.3 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 rece
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