The Effect of Ashless Antioxidants Type on Friction Reduction Durability on Engine Oils Containing MoDTC

The addition of molybdenum dithiocarbamates (MoDTC) to engine oils improves the fuel economy of vehicles. This efficiency is gradually reduced with the depletion of MoDTC and zinc dithiophosphates (ZnDTP) due to oil oxidation. Recent engine oils need more antioxidants than before to fulfill the requirements demanded for oxidation stability, which may influence the duration of friction reduction. Because of this fully formulated oils containing MoDTC were aged and evaluated with engine tests to determine the effect of ashless antioxidants type on friction reduction durability. It revealed that friction reduction durability was strongly influenced by various kinds of antioxidants and hindered phenol (PHE) suppressed the extinction of MoDTC and ZnDTP to retain a low friction property that was two times more stable than diphenylamine. Otherwise, high oxidation stability did not necessarily relate to a long duration of friction reduction. Engine oils containing PHE and MoDTC are revealed to have a long duration of friction reduction with GF-4 performance oxidation stability.