Automotive crankcase oils

Abstract

A modified open test tube type of apparatus has been used to assess the high-temperature oxidation stabilities of two grades of automotive crankcase oils and their base oils under conditions that simulate those encountered in the internal combustion engines. The method involved keeping the oil temperature at 180°C with an air flow of 1.0 L/min for 65 hours and evaluating the soluble oil acidity, pentane insolubles, volatile acidity and total oxidation products formed. The procedure detected that the oil acidity increased exponentially and sludge formation started after a threshold level of oxidation products had been formed. Volatility losses were found to be appreciable, and the antioxidant additives were quickly used up under the simulated conditions. Therefore only a mineral oil of high natural antioxidant capability could provide improved performance at high temperatures. The total oxidation product proved to be a valuable source of information on the extent of oil oxidation and oxidation stability study.