Studies on the Interchangeability of Group III Base Oils in ATF

We have compared five different, commercially produced, API Group III base oils in a next-generation, OEM automatic transmission fluid (ATF) formulation. One objective of this work is to understand the impact of base oil selection on the performance properties of finished ATF. This may help us to develop technically sound criteria for allowing interchange among premium Group III base oils in both factory-fill and service-fill ATFs. The performance data, measured from lab bench tests, include such properties as seal swell, low temperature viscometrics, oxidation life, and LVFA static and dynamic friction. Certain properties of the base oils, such as low temperature viscosity and oxidation stability, have a strong impact on the ATF performance. However, there are many chemical similarities between the Group III base oils, and this results in little to no differences observed in many performance areas. We also include comparisons of the same formulation made with typical Group I and II base oils.