At SAE’s request, ASTM developed both an oil pumpability engine test and a bench test, the Mini-Rotary Viscometer (MRV). The MRV data correlated well with the full scale engine pumpability data. SAE then incorporated MRV requirements for Winter Grade oils into the Viscosity Classification System J-300 SEP80.
A large number of engine oil pumpability failures occurred during the winter of 1980–81. In early 1981, ASTM, SAE and several companies started crash programs to solve the problem. These programs showed that those failure oils had a different sensitivity to cooldown cycle than the Pumpability Reference Oils (PROs) used in the original correlations. The cooldown cycle in the Federal Stable Pour Test appeared to better predict the 1980–81 failure oils, whereas the D3829 MRV cooldown cycle predicted the original PROs the best. Therefore, the Federal Stable Pour Test in combination with the Mini-Rotary Viscometer was recommended as a “stop-gap” measure.
Short term, ASTM organized a Federal Stable Pour Test Task Force to gather information on the Federal test method. This Task Force is now running a round-robin program with this test, using two different cooling cycles. Longer term, progress is being made in defining a new MRV cooldown cycle that will identify all oils having unacceptable engine pumpability in the field. Work is also progressing with a Liquid Bath Brookfield Scanning procedure.