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Extensive field test data have been obtained which can serve as a basis for evaluating the ability of various laboratory methods to predict the shear stability of multigrade crankcase oils. This basis was developed by determining the average viscosity changes of one single grade and 12 multigrade reference oils in six separate car fleets. The 12 multigrade oils were formulated with all of the chemical types of V.I. improvers currently in use, or likely to be used, in the near future. As a second part of the program, four types of bench tests and three different laboratory engine tests were evaluated for their ability to predict the average viscosity changes of the 13 reference oils observed in the fleet tests. Correlation of the laboratory method results with the field data was marred by the nonconformance of two multigrade oils. This nonconformance was more noticeable in the bench test results than in the laboratory engine test data.

The inability of certain crankcase oils to flow and lubricate an engine at low temperature and the lack of a suitable bench test to predict this characteristic are of current concern to engine builders and oil formulators. Two critical areas of oil flow at very low temperatures have been recognized by SAE and ASTM subcommittees. These are: the ability of an oil to flow to the oil screen of an engine fast enough to prevent “air binding,” and its ability to be drawn through the oil screen and pump inlet tubing without causing “pump cavitation.” The interrelation between these two factors is discussed and some engine pumpability data are presented which illustrate how one of these factors may affect the other. Descriptions of four new bench tests are presented along with data to show their ability to predict the low-temperature pumpability properties of crankcase oils.

Base stock and additive combinations were evaluated in the Cold Cranking Simulator (CCS) to determine their effects upon the viscosity of crankcase lubricants at 0 F. The interaction of polymeric additives with base stock wax was defined, and the role of base stock V.I. in cold cranking, ascertained. These factors were found to govern optimum selection of base stocks and polymeric additives in formulating multigrade crankcase oils.