Engine Testing Comparison of the Relative Oxidation Stability Performance of Two Engine Oils 952530

The relative oxidation stability of two fully formulated engine oils was compared in three testing methods by following the increase in kinematic viscosity of the oil. The purpose of the study was to determine the cause of the completely opposite ranking of the oxidation stability of the two oils that was observed in the ASTM Sequence IIIE engine test and the JASO M333 93 engine test and to determine the degree of correlation the two engine tests had with the field. The study consisted of laboratory oxidation testing, engine testing and taxi field testing to cover the range of conditions from controlled oxidation to actual driving conditions.

The laboratory and engine testing results showed that a likely reason for the discrepancy between the Sequence IIIE engine test and the JASO M333 93 engine test for these two oils was a potential interaction between catalytic Fe in the oil arising from wear and the formulation chemistry of the two oils: one oil contained Cu in the formulation while the other did not. Since these were industry reference oils and their exact chemical composition is unknown, other chemistry effects may be important though unresolved in this study. In a relative ordering of the two oils, the Cu containing oil was more oxidatively stable in tests where soluble Fe was present and the non-Cu oil was more oxidatively stable in tests where there was a low or zero concentration of Fe in the oil.

Furthermore, the extent of the Fe and Cu interaction was dependent on testing conditions. The biggest effect of the interaction was observed in laboratory tests followed by engine testing. The taxi field test showed the least effect with both oils showing equivalent viscosity increase up to 15,000 Km drain interval without influence of the type of chemistry. The relative ordering of the two oils that was seen in the Sequence IIIE and the JASO test was not observed in the taxi field test.