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The deterioration of the friction reducing properties of engine oils containing molybdenum dithiocarbamates (MoDTCs) in service was studied. A quantitative analysis of MoDTCs and zinc dithiophosphates (ZDTPs) remaining in aged oils revealed that ZDTPs were consumed faster than MoDTCs. The consumption rate of ZDTPs was slow in the presence of MoDTCs and peroxide-decomposing antioxidants. The frictional properties of aged oils were evaluated with a reciprocating friction tester (SRV tester). The friction coefficient measured with the SRV tester was correlated to the properties of the aged oils, such as the TAN increase, TBN, and concentration of remaining ZDTPs.

An SAE 5W-20 ILSAC GF-2 gasoline engine oil, which improves vehicle fuel efficiency by more than 1.5% relative to conventional SAE 5W-30 gasoline engine oils, was newly developed. And the target that 1.5% fuel efficiency improvement remains more than 10,000km was also achieved. The viscosity of this oil was optimized to satisfy both fuel economy and anti-wear performances. MoDTC and thiadiazole were added to achieve the target.

Some magnesium detergents in engine oil are reported to form sludge of needle crystals in the presence of carbon dioxide and water We tried to reproduce needle crystals in a beaker test and studied factors in needle crystal formation by magnesium detergents We found that overbased components of magnesium detergents dissolved in carbonic acid water formed needle crystals recrystallizing We also found the quantities of needle crystals increased when both carbon dioxide and water content in oil increased Moreover we clarified the quantities and sizes of needle crystals differed by magnesium detergents