Performance of Multigrade Oils in Off-Highway Diesel Engines

A number of multigrade diesel engine oils meeting API Service Classification CD, including those of Super Tractor Oil Universal (STUO) type, were tested in a standard multicylinder diesel test engine. The range in performance of these commercial oils in regard to piston deposits, wear, oil deterioration, and oil consumption was wide, but similar to that of SAE 30 oils of the same Service Classification. The wide variability in oil performance indicates engine oil test criteria of API Service Classification CD do not adequately address the concerns of diesel engine manufacturers. A new performance classification above and beyond API Service Classification CD is needed.