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Over fifty lubricating base oils from various crude sources and processing technologies, including ten re-refined base oils, have been studied. An SE/CC additive package was added to the base oils and the effects of the additives on oxidation stability of the oils were measured by a thin film oxygen uptake test. This oxidation test has demonstrated correlation with ASTM engine sequence IIID viscosity increase results. Chemical composition parameters such as sulfur, nitrogen, basic nitrogen, polar, saturate, and aromatic contents were systematically examined for correlation with the effects of additives on oxidation stability. Combinations of these compositional parameters were also investigated. Large differences in oxidation induction times of the various basestocks were found. Some of the differences could be related to the saturate and the sulfur content of the base oils.

A novel thermogravimetric analysis test method has been developed for the evaluation of lubricants. It involves superimposing the thermogravimetric trace of the sample in argon over the trace produced in oxygen atmosphere. The difference of the two traces indicates the oxidative influence on volatility as well as on the formation tendencies of high boiling (high molecular weight) oxidation products. The method was illustrated with a base oil with and without a catalyst package and an additive package. The test method is potentially useful for lubricant screening, quality control, and base oil composition effects on thermal oxidative stability.