Evaluation of Automotive Crankcase Lubricants by Differential Scanning Calorimetry

A LABORATORY BENCH TEST has been developed to examine the oxidation stability of crankcase lubricants using a high pressure power-compensation differential scanning calorimeter (DSC). Oxidation induction time measured at 175 °C and 3.62 MPa (525 psia) oxygen pressure was used to rank eight ASTM sequence IIID engine test stand reference oils. The DSC result correlated with the viscosity increase tendencies of the reference oils as determined by the engine tests. The new test method is rapid and requires only microliter sample size for testing with good precision. The method employs a mixture of soluble metal catalysts consisting of lead, iron, copper, manganese, and tin (82%, 7%, 4%, 3.5%, 3.5%) together with a synthetic oxidized high-boiling gasoline fraction. This combination was found necessary to simulate some of the engine conditions and chemistry.

Laboratory tests which could assess the performance of lubricants in engines have long been sought. Such tests could be used by lubricant developers to screen lubricants and lubricant formulations, to aid development of products and processes, and to minimize the expenses for engine tests. This paper reports the development of a differential scanning calorimeter test method to evaluate the oxidation stability of lubricants under the ASTM Sequence IIID engine test conditions.