The Effect of VI Improvers and Resultant Base Oil Volatility on Automotive Oil Economy with SAE 5W-40 Oils

This work was conducted to evaluate the effects resulting from the use of various VI improvers in multigrade engine oils on automobile oil economy. The test oils were formulated to be of similar viscosity in the SAE 5W-40 viscosity grade. The VI improvers tested covered a range of permanent shear stability, temporary shear stability and thickening characteristics.

Engine oil volatility was the only variable which could be identified as having a significant effect on automobile oil economy. The oils containing the styrene/diene VI improver were less volatile than all other oils tested and provided statistically significant improvements in oil economy. Permanent shear stability, high temperature/high shear viscosity, and in-use (used-oil) viscosity could not be identified as having a significant effect on automobile oil economy of the SAE 5W-40 oils studied.