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This study evaluates the shear-thinning effects of a commercial Viscosity Index (VI) improver in a variety of mineral oil base stocks to produce a series of viscosity grades from 0W-20 to 20W-50. All of these fluids also include a DI package in addition to an olefin copolymer VI improver and base oil. The Penn State high shear capillary viscometer was used to collect the primary data at shear rates of up to 106 s-1 and at 10 to 177°C. Data are fitted to a double truncated power law model to determine the incipient non-Newtonian shear rate Υ̇1, the power law index n, and the incipient second Newtonian shear rate Υ̇2. These parameters are found to be smooth functions of temperature and polymer concentration in the different base stocks. Using the data obtained from OW-20, 10W-30, and 20W-50 SAE grade formulations, these parameters (Υ̇1, Υ̇2 and n) are correlated as functions of temperature, polymer concentration, and a viscosity temperature property of the base oil.