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Higher soot levels in the crankcase oil may be an unavoidable result of lower exhaust-emissions. This study demonstrates that high soot levels in the oil can be dispersed, viscosity increases minimized, and filter plugging prevented by selecting the proper type of ashless dispersant and V.I. improver.

Fleet customers demand reduced operating costs. This necessitates the development of engine oils which can provide maximum fuel economy and extended oil drains, while still maintaining engine durability. This is particularly important in diesel engines produced since October 1998. These engines use retarded timing to meet EPA's emission requirements and, as a consequence in some cases, generate high soot levels in the engine oil. Extended oil drains in 1995 Caterpillar 3406E and 1996 Detroit Diesel Series 60 engines found no statistical difference in fuel economy or wear between a synthetic SAE 5W-40 and an SAE 15W-40 using API Group II base stocks. Both oils had the same API CG-4/SJ quality level. Soot levels at oil drains of 40,000-50,000 miles (64,372 - 80,465 km) ranged from 0.5-1.2%.

Starting in October 1993, the sulfur in diesel fuel will be lowered from 0.27 wt % average to 0.05 wt % maximum in order to reduce particulate sulfate emissions from on-highway vehicles. Given such a major change in diesel fuel, the study reported here focused on determining the most appropriate crankcase oils to choose. Using low-sulfur fuel, the study assessed the effects of crankcase oils on: emissions, wear, deposits, oil consumption, viscosity, and Total Base Number (TBN) depletion rates. The engines used were 1994 engines with low oil consumption and direct injection, such as the Detroit Diesel Company (DDC) Series 60, Caterpillar 3176B, Mack E-7, and the Caterpillar single-cylinder engine, which will be used in establishing the next oil category to be announced in 1995. The oils evaluated were SAE 10W-30 and 15W-40 oils with sulfated-ash levels of 1.0, 0.5, and 0.0 wt %.