The automotive and oil industries are continuing their efforts to improve fuel economy through lubricant modifications. As part of this program, fuel economy with experimental and commercial friction-modified engine oils has been measured in EPA 55/45 and road tests. These oils contained either soluble or insoluble friction-modifying additives.
Each of the experimental oils containing soluble friction-modifying additives was produced by blending an additive with a commercial engine oil. 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. Fuel economy with each oil was compared to that obtained using a commercial nonfriction-modified oil supplied by the marketer of the friction-modified oil. Each comparison was made using one car to eliminate car-to-car variability. 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.