Predicting Low Temperature Engine Oil Pumpability with the Mini-Rotary Viscometer

A new viscometer, the Mini-Rotary Viscometer (MRV), has been demonstrated to predict the low temperature pumpability performance of engine oils. This bench test method was developed at the request of SAE Fuels and Lubricants Subcommittee 2 and culminates a two-part ASTM Program to (1) define pumpability characteristics of reference oils in engines and (2) assess/develop bench test methods for predicting low temperature engine pumpability. The MRV is a low shear stress/shear rate viscometer that correlates either with an “average” engine or an individual engine, depending upon the critical rheological requirements of the particular engine or engines, and attains its high degree of correlation by predicting either of two failure modes-air binding of the pump or insufficient oil flow rate to the oil pump inlet. Thus, the MRV complements the Cold Cranking Simulator, a high shear stress device, in defining the low temperature behavior of straight-grade and multigrade engine oils.