The Relative Effectiveness of V.I. Improvers on an In-Service Viscosity Basis

It has been shown that the concentration of V.I. improver polymer required to give a predicted residual viscosity lift in a given base oil, after a shear stability test related to over-the-road performance, is relatively independent of the Shear Stability Index of the polymer over a wide range of shear stability level. Evidence is included which indicates that the high-temperature diesel engine performance of polymethacrylate V.I. improvers is related to the concentration of polymer in the lubricant and independent of the dispersancy capabilities of the polymer.

These findings have demonstrated that the use of a predicted in-service viscosity instead of a point-of-sale viscosity as a specification target has a significant effect on the selection of the V.I. improver for use in a lubricant. In particular, it becomes practicable to use more shear stable V.I. improvers than were formerly used.