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THE PENN STATE MICROOXIDATION TEST has been shown to be useful for the study of the influence of non-volatile compounds such as metal salts on the oxidative behavior of lubricants. A pressurized microoxidation test has been developed to evaluate the effects of water, NOx, and blow-by products on the stability of fully formulated motor oils. In this evaluation, H2O, N2O and metal salts of organic acids have been evaluated as single contaminants and in various combinations at test temperatures of 150°C and 175°C. In general, these studies show that water alone and in combination with the other contaminating products produces a substantial deposit under mild oxidation conditions such as oxidation at 175°C for less than ten hours. Under somewhat more severe conditions (175°C, time > 15 hours), relatively large amounts of soluble iron salts appear to dominate the deposition process.