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This paper provides an overview of gear lubrication related to automotive equipment. A brief background in various aspects of lubrication, including lubrication theory, lubricant evaluation, performance designations, and formulation technology, is presented. This information is designed to assist those involved in the selection of automotive gear lubricants.

The authors provide evidence indicating that oils meeting only the minimum requirements of API GL-5 do not always provide adequate gear protection, especially in severe duty applications. Increases in commercial vehicle power and loading have accentuated the need for oils of greater load carrying ability. A modified version of the standard L-37 test may help identify oils that possess superior durability and thermal characteristics. Future gear lubricants should provide improved fuel economy, increased manual transmission life; and frictional characteristics that allow noise free performance in limited slip differentials.

In order to assess the field needs of engine oils to be used in methanol-fueled vehicles, six oils were run in a fleet test over a ten-month period under short-trip service conditions. The results from the field test were compared with results with the six oils in the laboratory engine tests which have been used to predict field performance with methanol fuel. A lack of correlation between the field test and the laboratory engine tests suggests that the laboratory tests need revisions to better serve field needs.

The functions of engine oil are reviewed. The chemistry of engine oil additives and synthetics is described in terms for the non-chemist. The latest SAE engine oil viscosity classifications and API service designations are detailed. Developments underway to upgrade engine oil quality are discussed.