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Applying lubricants is one of the most important measures to reduce friction and wear. Improving the mechanical efficiency of engines and gears by reducing the frictional losses in the mixed film and in the fluid film lubrication regime in principle facilitates the reduction of fuel consumption of the engine or of the energy needed to operate the cars. The maximum consumption reduction that is theoretically possible with lubricating measures is estimated by means of the efficiency analysis of engines and gears and the proportionate effects of lower viscosity and additives reducing friction are evaluated. The estimate is made on the basis of the given relationship between friction and fuel consumption. Obviously, the possible consumption reductions at partial loads and lower temperatures are higher than at full load and operating temperature. This determines the relevant consequences regarding the possible total energy reductions under political economy aspects.

Viscosity represents the most important single property of any lubricant for internal combustion engines. The reason for this fact is that viscosity controls friction or lubrication regimes and consequently wear and performance life of the engine. Because of viscosity depending on temperature, pressure, and often shear rate, the local viscosity at the frictional contacts defined as effective viscosity will be responsible for the friction and wear situation at a specific location within the engine.