Laboratory Methods for Predicting the Viscosity Loss of Polymer Thickened Hydraulic Fluids

The viscosity stability of automatic transmission fluids as measured by the sonic oscillator failed to correlate with that determined in continuous high speed driving. The development of a test based on the use of a power steering pump is described. The effects of motor speed, oil pressure, and oil temperature were determined. Test conditions are described which permit prediction of used oil viscosities for transmission fluids. This test is independent of the chemical class of the V.I. improver.