LOW TEMPERATURE VISCOSITY OF DRIVE LINE LUBRICANTS IN A CONSTANT SHEER STRESS VISCOMETER: ASTM D6821
EXPLANATION
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, 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 relubricating 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. The low temperature performance of the drive line lubricant flow characteristics was originally evaluated by 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. The channel test was replaced by Test Method ASTM D2983. The results of this Test Method ASTM D6821 correlates with the viscometric measurements obtained in the Test Method ASTM D2983 by multiplying the latter data with 0.941.

This test method is applicable to drive line lubricants (gear oils, automatic transmission fluids, etc.) with a constant shear stress viscometer at temperatures from -40 to 10° C after a prescribed preheat and controlled cooling to the final test temperature. The applicability of this test method to petroleum products other than drive line lubricants has not been determined.

TEST SUMMARY
A drive line fluid is preheated to 50° C for a specified time, and then cooled at a programmed rate 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.

TEST PRECISION
Repeatability: 10.3 % of the mean
Reproducibility: 17.2 % of the mean

There is no accepted reference material suitable for determining the bias of this test method, hence, no statement of bias can be made.