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A series of SAE 5W-30 and SAE 10W-30 engine oils was evaluated in a New York City taxi fleet to study the performance of prototype API SG engine oils. Key formulation variables studied were SAE viscosity grade and Viscosity Index improver chemistry. A good correlation was established between Sequence VE sludge and varnish results and field performance. The deposit control value of dispersant Viscosity Index improvers was demonstrated. Formulations based on polymethacrylate Viscosity Index improvers performed directionally better in the field than the Sequence VE results predicted. Overall, the field performance of API SG quality oils was excellent.

Since 1985 we have conducted an extensive series of low temperature pumpability studies in two heavy duty diesel engines, the Cummins NTC-400 and the Mercedes-Benz OM 442A. This work has focused primarily on the influence of the Viscosity Index (VI) improver on the low temperature pumpability performance of SAE 15W-40, SAE 10W-30 and SAE 10W-40 engine oils. In addition, we have also addressed the issue of whether or not the current SAE J300 MRV viscosity limit is appropriate for engine oils used in heavy duty diesel engines. Since the MRV viscosity limit is based on a correlation with the pumpability performance of early 1970's model gasoline engines, it would not be surprising if the 30 Pa.s viscosity limit was inappropriate for modern heavy duty diesel engines. This paper focuses on work in the OM 442A engine. The results indicate, that for this engine the current MRV limit of 30 Pa.s is considerably higher then is warranted by actual engine pumpability results.