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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.

It is generally accepted that significant gains in fuel economy can be accomplished by reducing friction between the moving surfaces in key engine components (e.g. valvetrain, piston, crankshaft). This paper provides an overview of how specific tribological/rheological properties (e.g. viscosity, volatility, friction coefficient, film thickness, wear volume) can be considered in the design of fuel efficient crankcase engine lubricants that promote high wear resistance. Here, an example in how base stock, viscosity modifier (VM) and friction modifier (FM) can impact the surface friction is given. Friction and wear measurements from bench level lubrication characterization test methods mainly, high frequency reciprocating rig (HFRR) and mini-traction machine (MTM), are presented.