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Fuel economy with experimental and commercial friction-modified engine oils has been measured in EPA 55/45 and road tests. Fuel economy improvements provided by the additives averaged 1.2 percent in road tests. Adding molybdenum disulfide to both the engine oil and rear axle lubricant improved EPA 55/45 test fuel economy 4.6 percent. Three commercial friction-modified engine oils were evaluated. In EPA and road tests, fuel economy with these oils improved an average 2.9 and 4.1 percent, respectively, over that obtained using the nonfriction-modified engine oils. Of these oils, the two containing soluble additives were most effective in improving fuel economy under warmed-up operation, whereas the graphite-containing oil was most effective during engine warm-up.

Effects of reducing engine oil and rear axle lubricant viscosities on fuel economy were determined in EPA combined City and Highway (EPA 55/45) tests and in road tests, using four different sized cars. In EPA 55/45 tests, fuel economy rating improvements averaged about 1.5 percent; warmed-up and cold-start road test fuel economy improvements averaged about 4 and 8 percent, respectively. /GMRL/