ASTM D6821-02(2007)

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.

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 D 2983 in 1971.

The results of this test procedure correlate with the viscometric measurements obtained in Test Method D 2983. The correlation obtained is:

The equation was obtained by forcing the fit through zero. The coefficient of variation (R²) for this correlation is 0.9948.

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 to 10°C after a prescribed preheat and controlled cooling to the final test temperature.

1.2 The applicability of this particular test method to petroleum products other than drive line lubricants has not been determined.

1.3 This test method uses the millipascal second (mPa·s) as the unit of viscosity. One millipascal second is equal to one centipoise.

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 and health practices and determine the applicability of regulatory limitations prior to use.