A Study of Lengthened Engine Oil-Change Intervals

Lengthening the engine oil-change interval would reduce the frequency of automotive maintenance, reduce the amount of oil required to service the car population, and reduce the potential pollution problem resulting from the disposal of the used oil.

Tests were run using 1967-1972 model U.S. passenger cars, operating in several types of service. Using unleaded instead of leaded gasoline reduced deposits and wear. With unleaded gasoline, doubling the oil-change interval had no significant effect on deposits and wear, but did increase oil filter plugging frequency. Deposits and wear were less with unleaded gasoline and doubled oil-change interval than with leaded gasoline and “standard” oil-change interval. Doubling the concentration of additives used in current quality oils was more effective at reducing deposits and wear than was doubling the engine crankcase ventilation rate.

These studies indicate the feasibility of eventually lengthening the engine oil-change interval for General Motors (GM) cars provided that only unleaded gasoline and SE, or better quality, engine oils are used.