Recent additions to and modifications of automobile engines have significantly increased engine operating temperatures. There is concern about the effect of temperature increases on engine wear, but little, other than watching for the appearance of field problems has been reported. The effect of viscosity on wear was eliminated in this study by keeping viscosity constant while varying temperature. Under conditions which simulate valve train contact, it was found that wear increased approximately 3-fold over the temperature range 50° to 116°C. This increased wear, coupled with decreased viscosity with increasing temperature, leads to a potentially serious wear environment. Analysis of the data and comparison with possible mechanisms indicate that equilibrium adsorption of the antiwear additive is the controlling step in wear protection. Direct reaction of the antiwear additive with the surface at the higher temperatures had little, if any, contribution toward wear protection.Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in Washington, D.C., October 5–7, 1982.