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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.

More than 250 participants from 18 countries attended this meeting offering a total of 24 papers presented by speakers from 11 countries. The program of the colloquium provided an almost complete review of the present state of technology in the field of multigrade engine oils and their development. Besides the requirements of engines for specific engine oils and the fundamentals of rheology, the following main subjects were discussed: Viscosity classification of engine oils development in the USA and in Europe; Chemical and physical properties of viscosity index improvers; Cold flow behavior and high temperature viscosity of VI-improver containing oils; Influence of mechanical, thermal, and oxidative stresses; Engine performance of multigrade engine oils; Startability and pumpability of engine, oils. Some of the more important results and conclusions related to the subject of the relationship of engine oil viscosity to engine performance are reported and discussed.

Investigations using 4 monograde and 3 multigrade engine oils were performed by cold cranking an automotive engine to determine whether or not there is friction reduction due to the pseudoplastic behaviour of the multigrade engine oils. A comparison of the oils using viscometers indicated the viscometers ability to predict the “engine viscosities” over a temperature and shear rate range. Furthermore, this work determined whether results of viscometric measurements could be confirmed with the test engine. An answer was found to the question of the amount of hydrodynamic friction encountered when starting an automotive engine at low temperatures.

The relationship between the cold starting and and cold pumpability properties of multigrade engine oils is examined. The reasons why the high shear rate viscosities obtained with the CCS viscometer predicts an oil's startability characteristics but not its pumpability properties are discussed. The concept of viscosity versus shear rate curves at various temperatures are used to compare engine oils formulated with different VI improvers. Viscosity versus shear rate curves obtained with a pressurized capillary viscometer are compared to those obtained with a rotary viscometer. Finally, actual oil flow data obtained with a simulated engine gallery was shown to correlate with viscosity data obtained at a selected shear rate.