TEST SUMMARY
This test method covers the laboratory determination of high-temperature high-shear (HTHS) viscosity of engine oils at a temperature of 150° C using a multicell capillary viscometer containing pressure, temperature, and timing instrumentation. The shear rate for this test method corresponds to an apparent shear rate at the wall of 1.5 million reciprocal seconds 1.5 x 10(6)s(-1). This shear rate has been found to decrease the discrepancy between this test method and other high-temperature high-shear test methods used for engine oil specifications. Viscosities are determined directly from calibrations that have been established with Newtonian oils with viscosities from 2 to 7 mPa•s at 150° C.
The viscosity of the test oil in any of the viscometric cells is obtained by determining the pressure required to achieve a flow rate corresponding to an apparent shear rate at the wall of 1.5 x 10(6)s(−1). The calibration of each cell is used to determine the viscosity corresponding to the measured pressure.
Each viscometric cell is calibrated by establishing the relationship between pressure and flow rate for a series of Newtonian oils of known viscosity.
HTHS TESTS PRECISION
