Engine oil fuel efficiency - Practical issues

Engine oil plays an important role in improving fuel efficiency of gasoline internal combustion engines. Engine manufacturers strive to maximize oil contributions to fuel economy to meet future, more stringent targets of governmental regulations, improve energy resource utilization, minimize CO2 emissions, and last but not least, to satisfy their customers. To achieve these improvements engine manufacturers are developing or sponsoring development of engine tests to evaluate fuel efficiency of engine oils. These tests, during the period of their development and introduction, are the major driving force leading to improvement of engine oil-derived fuel efficiency. In the U.S.A., work is in progress on the development of a new Sequence VIE test which is planned for introduction in the years 2000-2001. The most important improvement in Sequence VIE will be in oil aging conditions and the extent to which these conditions will match oil aging reached at the end of 4,000-6,000 accumulated miles mandated prior to running the EPA M/H fuel economy test for CAFE. Incorporating more extensive aging in Sequence VIE will require substantially improved retention of engine fuel efficiency. This improvement can be achieved through minimizing viscosity increase and achieving and maintaining low boundary friction. Special attention should be given to interactions of additives among themselves and with base oil during the aging process. Our studies of chemical interactions and their effects on friction reducing capabilities of a molybdenum dialkyldithiocarbamate/zinc dialkyldithiophosphate additive system, used in formulation of advanced low friction/low viscosity engine oils, illustrate the importance of these interactions. Results of our investigations clearly show that further improvements and optimization of fuel efficiency are possible but require an understanding of changes occurring during oil aging.