Mechanisms of Engine Wear and Engine Oil Degradation in Vehicles Using M85 or Gasoline

The results of several investigations indicate the extent to which driving cycle, oil formulation, and fuel type (either regular unleaded gasoline or M85) influence the nature and severity of engine-oil degradation and engine damage. Driving cycle greatly influenced mass loss of piston rings and main and connecting rod bearings. For example, short-trip, cold start service with M85 caused 80 times more wear of top piston rings per km of service than was observed in long-trip service with the same oil. The magnitude of engine oil degradation was also documented. Under freeway driving conditions, in which the engine oil warmed completely, service with M85 fuel caused approximately the same amount of oil degradation as was found with gasoline. In city service, several engine oil parameters (base number, accumulation of insoluble contaminants, viscosity) degraded twice as fast with gasoline as with M85.