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The time dependence of the electrical properties for several fully formulated engine oils was tracked during engine dynamometer tests. The pattern for the resistivity indicates the existence of two types of processes (fast ion-depleting and slow ion-releasing) whose existence cannot be inferred through standard engine oil analysis. After these processes have subsided, the change in the resistivity correlates with the change in oil viscosity. We show that the peak value of the resistivity at early test times correlates with oil performance longevity as determined from conventional oil analysis parameters. In addition, the permittivity can provide an early warning of a dangerously low oil level. The significance of the results and their consequences for on-board monitoring of oil life through sensing technology based on electrical ac impedance measurements are discussed.

Radiometric wear techniques have been applied to determine the effect of fuel-saving engine oils on journal bearing load capacity. A test machine which applied a unidirectional load to a radioactive test bearing was used to evaluate bearing load capacity. The onset of bearing wear with increasing load provided a direct measurement of fluid-film breakdown, which defined hydrodynamic bearing load capacity. From this, an “effective” lubricant viscosity was calculated by comparing the performance of non-Newtonian lubricants to the performance of Newtonian lubricants. Results show that for the oil formulations tested that employ either a low viscosity or a soluble friction modifier to reduce engine friction, there is a high correlation between high-shear viscosity and hydrodynamic load capacity. The use of an insoluble friction modifier resulted in a higher bearing load capacity than expected based on high-shear viscosity.