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Further fuel economy improvement of the internal combustion engine is indispensable for CO2 reduction in order to cope with serious global environmental problems. Although lowering the viscosity of engine oil is an effective way to improve fuel economy, it may reduce the wear resistance. Therefore, it is important to achieve both improved fuel economy and reliability. We have developed new 0W- 8 engine oil of ultra-low viscosity and achieved an improvement in fuel economy by 0.8% compared to the commercial 0W-16 engine oil. For this new oil, we reduced the friction coefficient under boundary lubrication regime by applying an oil film former and calcium borate detergent. The film former increased the oil film thickness without increasing the oil viscosity. The calcium borate detergent enhanced the friction reduction effect of molybdenum dithiocarbamate (MoDTC).

With the electrification of automobiles, such as hybridization, engines on these vehicles operate more frequently at low oil temperatures, while engines are more specifically run at low engine speed and high load condition for driving vehicles. Hence, engine oils are required to reduce their viscosity at low temperature for friction reduction to improve fuel economy and maintain high temperature viscosity enough to protect engine parts for robustness at the same time. This leads to the improvement of viscosity index, the "ultra-high viscosity index (UHVI)" concept. The novel engine oil technology with a new high performance polymer was investigated. One of experimental oils showed the 100°C viscosity equivalent to SAE 0W-16 grade and the better fuel economy than that of SAE 0W-8 oil by an engine motoring friction test.

Turbocharged downsized gasoline engines have been widely used in the market as one of the measures to improve fuel economy. Coking phenomena in the lubricating circuit of the turbocharger unit is a well-known issue that may affect turbocharger efficiency and durability. Laboratory rig test such as ASTM D6335 (TEOST 33C) has been used to predict this phenomenon as a part of engine oil performance requirements. On the other hand, laboratory tests sometimes have difficulty reproducing the actual mechanism of coking caused by engine oil degradation. Accumulation of insoluble material is one of the important gasoline engine oil degradation modes. The influence of temperature and insoluble concentration were investigated based on actual used engine oils collected in the field.