Assessment of Shear Stability Methods for European Engine Oils

The high temperature permanent and temporary viscosities of oils run in a diesel injector shear stability test were compared with similar data for two European laboratory engine tests. Low shear rate permanent viscosity losses for oils run in selected European cars were compared with laboratory data. Shear stability as commonly determined by the diesel injector test and low shear rate viscosity measurements does not permit adequate assessment of the shear stability of engine oils. The viscosities measured at high shear rates and high temperatures appear to provide a more useful dimension in the characterization of oils than do standard viscosity measurements. Temporary viscosity losses tend to be larger than permanent viscosity losses.