Adaptation of the Penn State Microoxidation Test for the Evaluation of Automotive Lubricants
The Penn State Microoxidation Test has been adapted for use with mineral oil base stocks and fully formulated automotive crankcase oils. Tests under nitrogen and air atmospheres coupled with analyses using gel permeation chromatography (GPC) and clay column adsorption provide for a semiquantitative analysis of the products by elution time (apparent molecular size). This test procedure allows for primary and secondary oxidation reaction rate studies after substantial quantities of the lubricant have been oxidized. Time-temperature studies can show the effectiveness of base oil quality as well as effects contributed by additives. A general time-temperature equivalence in the range of 200 to 225°C has been demonstrated for a series of formulated engine oils. Microoxidation tests have been compared with III-C hot engine tests for a series of ASTM reference oils.