Testing an Anti-Friction Coating in a Small Engine

This paper describes tests of friction-reducing coatings applied to single-cylinder, splash-lubricated, gasoline engines. The suppliers of the coatings anticipated a significant, (10-15%), decrease in fuel consumption as a result of covering most engine contact surfaces with a proprietary, FIFE-type plastic. However, a brief analysis indicates that possible benefits should be closer to 3% at high engine loads. To establish coating effectiveness, carefully controlled fuel economy testing of two engines was performed on a water-braise dynamometer at one engine speed and two output torque levels (approximately 70% and 95% of rated load). Test results showed increased fuel consumption on both coated engines compared with uncoated engines. Direct comparisons showed fuel consumption was 8% higher at full load and 10% higher at part load. This unexpected increase in fuel consumption was attributed to increased friction in the journal bearings of the engine. The coating interfered with the normal hydrodynamic lubrication,