Japanese original equipment manufacturers typically develop their own standards for engine oils used in heavy-duty trucks and motorcycles, but partner with North American counterparts to develop International Lubricant Standardization and Advisory Committee and American Petroleum Institute specs for passenger car motor oils. However, Japanese carmakers have pioneered the use of ultra-low-viscosity oils and now recommend use of SAE 0W-12 and SAE 0W-8 oils for some models. ILSAC GF-6, expected to be introduced in 2020, does not cover those viscosity grades.

[This] new engine oil needs high V.I. and low volatility, and Group III has better trade-off than I or II, said Yamamori Kazuo, project manager for Material Engineering Division No. 2 of Toyotas Tribology Material Department.

In general, a base oil with lower viscosity brings higher volatility, which can lead to oil evaporation and thickening. However, base oils with high viscosity index – which means they experience less change in viscosity related to temperature changes – tend to be less volatile.

Although base oil viscosity can be reduced, it is difficult to significantly reduce it unless synthetic base oil is used, Kazuo he told an audience at an ICIS Base Oils & Lubricants conference held here recently. This is because low-viscosity synthetic oils tend to have higher V.I. and lower volatility than low-viscosity mineral oils.

Viscosity modifier additives are used to improve V.I. However, moving from SAE 0W-20 oils to SAE 0W-16 oils is largely achieved by using less viscosity modifier, he explained. For SAE 0W-8 oils, there is little room for a viscosity modifier.

Kazuo said API Group III base oils enable formulation of 0W-XX products with 15 percent maximum Noack volatility to meet the GLV-1 specification for ultra-low-viscosity 0W-12 and 0W-8 passenger car motor oils. The Noack volatility test determines the evaporation loss of lubricants in high-temperature service.