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Eight SAE 10W-30 oils were formulated with different viscosity index (VI) improvers and used in single and multicylinder engines. A significant number of measurements were made during each engine test to accurately determine changes in kinematic viscosity with time. These measured values appear to decay logarithmically over a large portion of each test. This behavior is qualitatively similar to results reported in other engine tests involving multigrade oils. A coefficient in the data correlation is suggested as a measure of engine severity for a particular formulation. This coefficient and the shear stability index are used to monitor severity changes during the test period. These changes are correlated to an increase in ring gap and a decrease in ring mass for the single cylinder engine. A procedure is suggested for extrapolating severity measures to a value representative of the initial engine configuration.