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We closely studied the action mechanism and deterioration mechanism of ZDTP (zinc dialkyldithiophosphate), used as an essential additive in engine oils for over half a century, and determined that the sulfur in ZDTP was hampering efforts to improve oil life. With this in mind, we developed a completely new engine oil blended with ZP (zinc dialkylphosphate), in which oxygen replaces the sulfur in ZDTP, and conducted engine tests. The tests confirmed that the newly developed oil provides long service life that cannot be attained with conventional oil formulated with ZDTP.

A bench engine test for evaluating the fuel efficiency of automotive crankcase oils using modern engines was developed. The fuel consumption was primarily proportional to the viscosity of the oils down to 5 mm2/s at operating temperatures, indicating that the use of low-viscosity oil was effective in improving fuel efficiency. This may be because the oil film would be formed easily, since sliding parts, such as valve train systems, in modern engines are finely finished. Organo molybdenum dithiocarbamates were effective in improving fuel efficiency at high temperature. A 2.7% improvement in fuel efficiency relative to conventional SAE 10W-30 oils was achieved by the combination of low-viscosity SAE 5W-20 oils and organo molybdenum dithiocarbamates under constant operating conditions with engine speed 1,500 rpm and torque 37.2 N•m.