Better Prediction of Engine Oil Pumpability Through a More Effective MRV Cooling Cycle

The Kini-Rotary Viscometer (MRV), adopted by SAE in 1980 to predict engine oil pumpability, was unable to fail certain commercial oils that caused engine problems in the winter of 1980-81. The latter oils did fail in the seven-day Federal Stable Pour, Cycle C, Test (FSPCCT). A special study of the FSPCCT temperature cycle in the MRV highlighted the importance of a slow cooldown rate in the temperature range of engine oil cloud points. Using this principle, a modified one-day MRV test was developed that fails 1980-81 problem oils. Further modification, however, was required to detect a newly discovered problem oil, PRO-29, Failure-prone oils discovered since 1980 are very sensitive to subtle changes in cooling rate and temperature regime. As the industry proceeds to develop a more effective MRV test, a better insight into the pumpability problems of 1980-81 has been gained.