A Study of Lubricant Effects on Inlet Valve Deposits Using a Specially Adapted Test Vehicle

The increasing requirement to provide lubricants which assist in the efficient performance of engines has led to the study of valve deposits in a specially adapted gasoline engined road vehicle. The valve stem seals were removed from two of the four inlet valves. This has enabled the gross effects of lubricants on the total valve deposits to be studied over a period of 6,000 miles without oil change.

Four lubricants were studied in detail. The results were analysed with respect to lubricant effects on total valve deposits and any redistribution of deposits caused by the vehicle modification (inlet valve stem seal removed). These lubricants were also compared in standard field tests (36,000 miles) and selected European bench engine tests with respect to engine wear and deposits control. These data are compared with the results obtained in the modified vehicle valve deposits test. It was found that lubricant formulation influenced total valve deposits. General engine deposits & wear control for a particular lubricant does not necessarily correlate with total valve deposits formed. It was demonstrated that it was possible to formulate a lubricant to give excellent engine deposits & wear control, together with a low level of total valve deposits.