ASTM D6351 Determination of Low Temperature Fluidity and Appearance of Hydraulic Fluids
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 -22.9°C. Alternatively, a fluid can be evaluated at the lowest temperature expected for field service.
