Shear Stability of Multigrade Crankcase Oils in Cars, Laboratory Engine, and Bench Tests - (Report of the Mechanical Shear Stability Subsection, R & D Div. VII B-1 of ASTM Committee D-2) 720946

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 control oil (ARO-113), which did not contain a V.I. improver, showed a measurable viscosity increase in the 1500 mile field tests. This indicates that factors other than mechanical shear may have influenced the viscosity changes of the multigrade oils in the field tests.


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