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Engine oils are subjected to a series of industry standard engine dynamometer tests to measure their wear protection capability, sludge and varnish formation tendencies, and fuel efficiency among several other performance attributes before they are approved for use in customer engines. However, these performance attributes are measured at the end of tests and therefore, do not provide any information on how the properties have changed during the tests. In one of our previous studies it was observed that engine oil samples collected from fleet vehicles after 12,000 mile drain interval showed 10-15 % lower friction and more importantly, an order of magnitude lower wear rate than those of fresh oils. It was also observed that the composition of the tribochemical films formed was quite different on the surface tested with the drain oils from those formed with fresh oils.

The estimation of fuel economy benefits gained through improved engine oils using ASTM test procedures is expensive and time consuming. This paper describes a methodology to predict ASTM Sequence VI and VIA fuel economy based on laboratory bench tests. High shear rate viscosities were measured using a tapered bearing simulator and boundary friction coefficients were measured using a Plint reciprocating machine at temperatures used in Sequence VI and VIA tests. Weighted viscosities and weighted friction coefficients were calculated from these measurements using weighting factors identical to those used in the Sequence tests. The measured Sequence VI and VIA fuel economy numbers were correlated with the weighted viscosities and weighted friction coefficients. An excellent correlation was observed between Sequence VIA fuel economy and weighted high shear rate viscosities and friction coefficients whereas a reasonable correlation was observed for Sequence VI fuel economy.