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The argument over which values of oil viscosity best correlate with measures of engine operation has gone on for many years. Over a decade ago (1977), the membership of the Engine Oil Subcommittee of the Society of Automotive Engineers (SAE) Fuels and Lubricants Committee (now the Fuels and Lubricants Division) agreed that there were enough data to justify asking the appropriate ASTM subcommittee (D02.07) to develop methods for determining values of high-temperature, high-shear-rate (HTHS) oil viscosity and to relate them to engine operation. In 1984, an ASTM task force finished reviewing the available literature and composed a report that summarized the effects of viscosity on bearing oil film thickness, engine wear, engine friction, and fuel economy (ASTM DS-62). This paper reviews the findings of that report and updates them in light of recent studies. The case for incorporating HTHS viscosity specifications into the Engine Oil Viscosity Classification, SAE J300, is presently stronger than ever. Suggestions are offered on how this incorporation might be accomplished and on what future directions ASTM research on HTHS viscosity should take.
engine oil viscosity, elasticity, viscosity index (VI) improvers, shear rate, temperature, journal bearings, oil films, engine wear, fuel economy, engine durability, engine performance
Manager, General Motors Research Laboratories, 160 RMB, GM Technical Center, Warren, MI