Formulation changes in lubricating oils may be required to satisfy the needs of diesel engines meeting the exhaust emission limits scheduled for implementation in the United States during the 1990's. Compositional adjustments would be predicated on interactive engine/fuel/lubricant behavior. The dynamics of the interaction involve the mechanical engine design modifications necessary to achieve the standards, potential legislated limitations on fuel composition and the contribution of the lubricant itself to engine exhaust emissions, especially particulate emissions.An investigative program was undertaken using a 12.7 liter displacement Detroit Diesel Series 60 engine to explore these interactions. The effects of various speed/load/time/temperature cycles on engine deposits, wear, oil degradation, oil consumption and exhaust emissions are reported.“Part 1” of this study includes the results of four 250 hour tests using an SAE 15W-40, API CE baseline lubricant and 0.3% wt. sulfur fuel under extremely severe conditions.“Part 2” of this study includes the results of two, less severe, 500 hour tests using the same baseline lubricant with both 0.3% wt. and 0.05% wt. sulfur fuels.The data reveal a surprising insensitivity of the engine to operating conditions in terms of wear, deposits and oil consumption control. The use of low-sulfur fuel did not affect deposit-forming tendencies and had only modest effect on engine wear and lubricant degradation. Both the level of particulate emissions and the lubricant contribution to these emissions were shown to be highly dependent on operational parameters during the measurement, including lubricant consumption rate. The sulfur content of the fuel was seen to be more influential than lubricant consumption on the particulate emission level and deterioration rate.Author's Note: “Part 1” of this study was previously presented as an oral address at the 1989 SAE International Congress and Exhibition, Session FL3.