The temperatures of engine oil, automatic transmission fluid, and differential lubricant were measured under a variety of steady-state conditions in 1969, 1971, 1972, and 1973 model year cars. Increases in engine speed and stroke and coolant temperature caused significant increases in engine oil temperatures. Engine load and coolant temperature increases appeared to be the principal causes of automatic transmission fluid temperature increases. Differential lubricant temperatures increased as engine speed and load increased, but speed was the more influential variable. The effect of ambient temperature was negligible in all cases over the narrow range of ambient temperatures investigated (65-85°F).Analysis of the data for year-to-year trends showed that only engine oil temperatures increased from 1969 to 1973. This trend, and several observations of engine oil temperatures greater than 300°F, suggest that improved resistance of engine oils to oxidative thickening may be required.