The SAE Engine Oil Viscosity Classification (EOVC) Task Force has been gathering data in consideration of extending SAE J300 to include engine oils with high temperature, high shear rate (HTHS) viscosity below the current minimum of 2.6 mPa⋅s for the SAE 20 grade. The driving force for doing so is fuel economy, although it is widely recognized that hardware durability can suffer if HTHS viscosity is too low. Several Japanese OEMs have expressed interest in revising SAE J300 to allow official designation of an engine oil viscosity category with HTHS viscosity below 2.6 mPa⋅s to enable the development of ultra-low-friction engines in the future. This paper summarizes the work of the SAE EOVC Low Viscosity Grade Working Group comprising members from OEMs, oil companies, additive companies and instrument manufacturers to explore adoption of one or more new viscosity grades. Past studies relating HTHS viscosity to engine wear will be reviewed, and an analysis of the rheological properties of commercial SAE xW-20 oils will be presented. New data will also be offered to demonstrate the feasibility of formulating engine lubricants to meet HTHS viscosities as low as 1.7 mPa⋅s while meeting current low-temperature oil starting viscosity and ILSAC volatility requirements. Finally, the paper will address the measurement precision of current HTHS methods on prototype low HTHS engine oils.
