Oxidation stability of gasoline engine lubricants: Effect of base‐oil chemistry in laboratory and engine tests

Abstract

Abstract This paper presents a laboratory test called the Iron Catalysed Oxidation Test (ICOT), where air is bubbled through an oil sample at 165 °C. This test, shorter than the CEC L‐48 test, provides an easy method of gasoline engine lubricant screening. A basic study has shown that this kind of test is suitable for the discrimination of base‐oil properties and that the oil viscosity increase at the end of the test is highly indicative of the oxidation processes at work. In this study, the base‐oil assessment is carried out with an API SG SAE 15W‐40 oil, and the results depend directly on the aromaticity of the base oil. Several engine test sequences, including CEC L‐55‐T‐95: TU3M HT, were also applied to these formulations, which differ only in their base oils. The results of those sequences where oil consumption was low roughly correlated with the laboratory test results. However, when there was a high loss of volatile matter in the engine tests, the oil viscosity increase was greatly modified, and this parameter can override the effect of oxidation.