ASTM D6351-22

Standard Test Method for Determination of Low Temperature Fluidity and Appearance of Hydraulic Fluids

SIGNIFICANCE AND USE
4.1 The temperature at which a lubricant remains fluid and homogeneous after seven days is an index of its ability to withstand prolonged exposure to cold temperature. With vegetable oils and some synthetic esters, it is necessary to do extended cold storage testing. Quick cool, short-term tests, such as Test Methods D97 and D2500, do not adequately predict the tendency to solidify over longer time spans at cold temperatures.  
4.2 This test method is not intended to indicate cold temperature pumpability performance. A separate assessment of viscometric performance should be made in order to assess cold flow properties, which are important in order to avoid system damage in cold temperature applications. Suitable guidelines for such testing and test temperatures for various viscosity grades can be found in Practice D6080.  
4.3 No specific temperature of measurement is given in this test method because fluids with different viscosity grades have different cold temperature performance expectations. For guidance on temperature selection relative to an intended low temperature viscosity grade or ISO VG, consult Practice D6080. As an example of using Practice D6080, a L22 viscosity grade would be evaluated at the lowest temperature for that grade, namely –22.9 °C. Alternatively, a fluid can be evaluated at the lowest temperature expected for field service.
SCOPE
1.1 This test method covers the fluidity and appearance of hydraulic fluids after storage at low temperature.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.2.1 Exception—In 6.1.1, the material is designated in cSt as this is the common name used for this type of oil.  
1.3 WARNING—Mercury has been designated by many regulatory agencies as a hazardous substance that can cause serious medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Use caution when handling mercury and mercury-containing products. See the applicable product Safety Data Sheet (SDS) for additional information. The potential exists that selling mercury or mercury-containing products, or both, is prohibited by local or national law. Users must determine legality of sales in their location.  
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.  For specific warning statements, see 1.3 and Section 6.  
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: 30-Apr-2022
• ICS: 75.120 - Hydraulic fluids
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.N0 - Hydraulic Fluids

Relations

• Refers: ASTM D6080-18a - Standard Practice for Defining the Viscosity Characteristics of Hydraulic Fluids
• Effective Date: 01-Oct-2018
• Refers: ASTM D6080-18 - Standard Practice for Defining the Viscosity Characteristics of Hydraulic Fluids
• Effective Date: 01-Jun-2018
• Refers: ASTM D2500-16 - Standard Test Method for Cloud Point of Petroleum Products
• Effective Date: 01-Jan-2016
• Refers: ASTM E1-13 - Standard Specification for ASTM Liquid-in-Glass Thermometers
• Effective Date: 01-May-2013
• Refers: ASTM D97-12 - Standard Test Method for Pour Point of Petroleum Products
• Effective Date: 01-Dec-2012
• Refers: ASTM D6080-12a - Standard Practice for Defining the Viscosity Characteristics of Hydraulic Fluids
• Effective Date: 01-Nov-2012
• Refers: ASTM D6080-12 - Standard Practice for Defining the Viscosity Characteristics of Hydraulic Fluids
• Effective Date: 01-Jun-2012
• Refers: ASTM D97-11 - Standard Test Method for Pour Point of Petroleum Products
• Effective Date: 01-Jun-2011
• Refers: ASTM D6080-10 - Standard Practice for Defining the Viscosity Characteristics of Hydraulic Fluids
• Effective Date: 01-May-2010
• Refers: ASTM D97-09 - Standard Test Method for Pour Point of Petroleum Products
• Effective Date: 15-Apr-2009
• Refers: ASTM D2500-09 - Standard Test Method for Cloud Point of Petroleum Products
• Effective Date: 15-Apr-2009
• Refers: ASTM D97-08 - Standard Test Method for Pour Point of Petroleum Products
• Effective Date: 01-Sep-2008
• Refers: ASTM D97-07 - Standard Test Method for Pour Point of Petroleum Products
• Effective Date: 01-Dec-2007
• Refers: ASTM D6080-97(2007) - Standard Practice for Defining the Viscosity Characteristics of Hydraulic Fluids
• Effective Date: 01-Nov-2007
• Refers: ASTM E1-07 - Standard Specification for ASTM Liquid-in-Glass Thermometers
• Effective Date: 01-Nov-2007

Overview

ASTM D6351-22 is the Standard Test Method for Determination of Low Temperature Fluidity and Appearance of Hydraulic Fluids. Developed by ASTM International, this method assesses the fluidity and visual condition of hydraulic fluids after extended storage at low temperatures. The standard is particularly significant for evaluating the stability of hydraulic oils-such as vegetable oils and synthetic esters-under cold storage conditions, where short-term tests may not adequately predict performance.

This test is crucial for hydraulic system reliability, especially in applications exposed to prolonged low temperatures. Ensuring that hydraulic fluids remain fluid and homogeneous helps prevent system failures and maintains operational efficiency in cold environments.

Key Topics

• Long-term Cold Stability: The method involves storing hydraulic fluid samples at a specified low temperature for seven days, after which their ability to flow and overall homogeneity are assessed.
• Visual Assessment: Samples are checked for clarity, haze, or opacity, as well as for the presence of crystals, particles, or phase separation.
• Applicable to Various Fluids: While especially important for vegetable oils and certain synthetic esters, this method is relevant for a broad range of hydraulic fluids.
• Temperature Flexibility: No fixed test temperature is specified; it should be chosen based on the fluid’s intended viscosity grade or expected service conditions, with guidance available in ASTM D6080.
• Safety Considerations: Special attention is advised if mercury or mercury-containing products are used, given health and environmental hazards.
• Not a Pumpability Test: This test does not measure cold temperature pumpability; viscometric tests per ASTM D6080 should be used for that assessment.

Applications

The ASTM D6351-22 test method is vital for:

• Hydraulic Equipment in Cold Climates: Ensuring fluid reliability in industrial machinery, mobile equipment, and off-highway vehicles exposed to low ambient temperatures.
• Product Development & Quality Control: Verifying the low-temperature characteristics of new formulations, particularly for bio-based and environmentally friendly hydraulic fluids.
• Compliance & Specification: Meeting manufacturer or regulatory requirements for hydraulic system performance in cold weather.
• Preventive Maintenance: Identifying potential issues such as gelling, phase separation, or loss of homogeneity before fluids are used in service.

Industries that benefit from this standard include construction, mining, transportation, military, and renewable energy sectors where hydraulic systems operate in cold environments.

Related Standards

• ASTM D97 - Test Method for Pour Point of Petroleum Products
  A common short-term test for determining the lowest temperature at which a fluid will flow.

• ASTM D2500 - Test Method for Cloud Point of Petroleum Products and Liquid Fuels
  Used to measure when wax crystals first appear during cooling.

• ASTM D6080 - Practice for Defining the Viscosity Characteristics of Hydraulic Fluids
  Provides guidance on test temperatures and viscosity classification for hydraulic fluids in cold flow scenarios.

• ASTM E1 - Specification for ASTM Liquid-in-Glass Thermometers
  Covers the temperature measurement devices required for precise low temperature testing.

Practical Value

Adhering to ASTM D6351-22 ensures hydraulic fluids are properly evaluated for fluidity and appearance after cold storage, supporting long-term equipment reliability and reducing downtime in low temperature conditions. By selecting appropriate test temperatures and following this standard, industries can more accurately predict field performance, safeguard against potential system issues, and comply with best practices in hydraulic fluid assessment.

Keywords: ASTM D6351, low temperature fluidity, hydraulic fluid appearance, cold storage test, hydraulic oil stability, hydraulic systems, cold weather performance

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: D6351 − 22
Standard Test Method for
Determination of Low Temperature Fluidity and Appearance
of Hydraulic Fluids
This standard is issued under the fixed designation D6351; 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* 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the fluidity and appearance of
D97 Test Method for Pour Point of Petroleum Products
hydraulic fluids after storage at low temperature.
D2500 Test Method for Cloud Point of Petroleum Products
1.2 The values stated in SI units are to be regarded as
and Liquid Fuels
standard. No other units of measurement are included in this
D6080 Practice for Defining the Viscosity Characteristics of
standard.
Hydraulic Fluids
E1 Specification for ASTM Liquid-in-Glass Thermometers
1.2.1 Exception—In 6.1.1, the material is designated in cSt
as this is the common name used for this type of oil.
3. Summary of Test Method
1.3 WARNING—Mercury has been designated by many
3.1 After preliminary drying to remove trace amounts of
regulatory agencies as a hazardous substance that can cause
water, the sample is cooled to a specified temperature. After
serious medical issues. Mercury, or its vapor, has been dem-
seven consecutive days, the sample is examined for its ability
onstrated to be hazardous to health and corrosive to materials.
to flow and observed for homogeneity.
Use caution when handling mercury and mercury-containing
products. See the applicable product Safety Data Sheet (SDS)
4. Significance and Use
for additional information. The potential exists that selling
4.1 The temperature at which a lubricant remains fluid and
mercury or mercury-containing products, or both, is prohibited
homogeneous after seven days is an index of its ability to
by local or national law. Users must determine legality of sales
withstand prolonged exposure to cold temperature. With veg-
in their location.
etable oils and some synthetic esters, it is necessary to do
1.4 This standard does not purport to address all of the
extended cold storage testing. Quick cool, short-term tests,
safety concerns, if any, associated with its use. It is the
such as Test Methods D97 and D2500, do not adequately
responsibility of the user of this standard to establish appro-
predict the tendency to solidify over longer time spans at cold
priate safety, health, and environmental practices and deter-
temperatures.
mine the applicability of regulatory limitations prior to use.
4.2 This test method is not intended to indicate cold
For specific warning statements, see 1.3 and Section 6.
temperature pumpability performance. A separate assessment
1.5 This international standard was developed in accor-
of viscometric performance should be made in order to assess
dance with internationally recognized principles on standard-
cold flow properties, which are important in order to avoid
ization established in the Decision on Principles for the
system damage in cold temperature applications. Suitable
Development of International Standards, Guides and Recom-
guidelines for such testing and test temperatures for various
mendations issued by the World Trade Organization Technical
viscosity grades can be found in Practice D6080.
Barriers to Trade (TBT) Committee.
4.3 No specific temperature of measurement is given in this
test method because fluids with different viscosity grades have
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.N0 on Hydraulic Fluids. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
CurrenteditionapprovedMay1,2022.PublishedJuly2022.Originallyapproved contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
in 1999. Last previous edition approved in 2016 as D6351 – 10 (2016). DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D6351-22. 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
D6351 − 22
different cold temperature performance expectations. For guid- fluid is water based, for example a water-glycol fluid, this
ance on temperature selection relative to an intended low drying step is to be omitted.
temperature viscosity grade or ISO VG, consult Practice
7.3 Close the test jar with the cork.
D6080. As an example of using Practice D6080, a L22
7.4 Prepare a temperature reference jar in accordance with
viscosity grade would be evaluated at the lowest temperature
7.1 with a liquid that will remain fluid at t
...

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: D6351 − 10 (Reapproved 2016) D6351 − 22
Standard Test Method for
Determination of Low Temperature Fluidity and Appearance
of Hydraulic Fluids
This standard is issued under the fixed designation D6351; 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 Scope*
1.1 This test method covers the fluidity and appearance of hydraulic fluids after storage at low temperature.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.2.1 Exception—In 6.1.1, the material is designated in cSt as this is the common name used for this type of oil.
1.3 WARNING—Mercury has been designated by many regulatory agencies as a hazardous materialsubstance that can cause
central nervous system, kidney and liver damage. serious medical issues. Mercury, or its vapor, may has been demonstrated to be
hazardous to health and corrosive to materials. Caution should be taken Use caution when handling mercury and mercury
containing mercury-containing products. See the applicable product Material Safety Data Sheet (MSDS) for details and EPA’s
website—http://www.epa.gov/mercury/faq.htm—for additional information. Users should be aware (SDS) for additional informa-
tion. The potential exists that selling mercury and/or mercury containing products into your state or country may be prohibited by
law.or mercury-containing products, or both, is prohibited by local or national law. Users must determine legality of sales in their
location.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. For specific warning statements, see 1.3 and Section 6.
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:
D97 Test Method for Pour Point of Petroleum Products
D2500 Test Method for Cloud Point of Petroleum Products and Liquid Fuels
D6080 Practice for Defining the Viscosity Characteristics of Hydraulic Fluids
E1 Specification for ASTM Liquid-in-Glass 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.N0 on Hydraulic Fluids.
Current edition approved June 15, 2016May 1, 2022. Published July 2016July 2022. Originally approved in 1999. Last previous edition approved in 20102016 as
D6351 – 10.D6351 – 10 (2016). DOI: 10.1520/D6351-10R16.10.1520/D6351-22.
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
D6351 − 22
3. Summary of Test Method
3.1 After preliminary drying to remove trace amounts of water, the sample is cooled to a specified temperature. After seven
consecutive days, the sample is examined for its ability to flow and observed for homogeneity.
4. Significance and Use
4.1 The temperature at which a lubricant remains fluid and homogeneous after seven days is an index of its ability to withstand
prolonged exposure to cold temperature. With vegetable oils and some synthetic esters, it is necessary to do extended cold storage
testing. Quick cool, short-term tests, such as Test Methods D97 and D2500, do not adequately predict the tendency to solidify over
longer time spans at cold temperatures.
4.2 This test method is not intended to indicate cold temperature pumpability performance. A separate assessment of viscometric
performance should be made in order to assess cold flow properties, which are important in order to avoid system damage in cold
temperature applications. Suitable guidelines for such testing and test temperatures for various viscosity grades can be found in
Practice D6080.
4.3 No specific temperature of measurement is given in this test method because fluids with different viscosity grades have
different cold temperature performance expectations. For guidance on temperature selection relative to an intended low
temperature viscosity grade or ISO VG, consult Practice D6080. As an example of using Practice D6080, a L22 viscosity grade
would be evaluated at the lowest temperature for that grade, namely –22.
...