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A test procedure has been developed to investigate the effect of lubricating oils on the mechanical efficiency of car manual transmissions. The test is based on the measurement of the power dissipated in a closed mechanical loop, in order to allow for better precision compared to traditional output power measurements. The test apparatus fits two equal transmissions, operated by an electric motor. For the present investigation, two Fiat 126 car transmissions were used and a two load stage test procedure was adopted. Lubricating oils having different rheological and compositional characteristics have been tested. Test results discussed in terms of the effects of operating parameters and oil characteristics on transmission efficiency indicate significant advantages for oils containing synthetic basestocks and friction modifiers. Correlation of the test with friction measurements performed with a conventional tribometer is also considered.

Test severity, inhibition and oil discrepancy: these are factors which influence the formation of sludge and the extent of its settling in the engine. By appropriate used-oil analyses it is possible to calculate indices of the oil's performance which are largely independent of the type of engine used and the test procedure followed. The ASTM D 893 test procedure is inapplicable to a large number of modern motor oils. An alternative method based on the filtration of used oils over membrane filters has been of great help in recent years. However, a newly developed photometric method seems promising in overcoming most present analytical difficulties. The indices obtained from used-oil analyses can become the only feasible test method in the development of long drain oils.

The use of several different synthetic lubricants in the formulation of multigrade motor oils is examined from the point of view of their physical and chemical characteristics and their commercial suitability. The influence of synthetic lubricant bases upon some of the performance characteristics of conventional additives has been considered. Engine test results using an SAE 10W/50 oil containing an ester base are compared with the performance of a similar SAE grade motor oil based upon mineral oil alone.