Low Temperature Viscosity Characteristics of Used Engine Oils

Abstract

Data from a Society of Automotive Engineers (SAE) fuels and lubricants investigation are presented to depict the viscosity increase at minus 18 degrees C of crankcase oils as a function of mileage, engine type, service type, viscosity grade, and base oil type (petroleum or synthetic). The total data base of 1530 viscosity measurements was classified to show the viscosity increase for each major viscosity grade. It was found that SAE 10W/20, SAE 10W/30, SAE 10W/40, and SAE 10W/50 oils increased in viscosity at the same rate, and that half of all SAE 5W-X and SAE 10W-X oils went out of grade by 2500 mi. of use. SAE 15W-X and SAE 20W-X oils showed better stability, remaining in their low temperature viscosity grades for about 11,000 mi. Partial synthetics/total synthetics increased at a slower rate and to a lower level than all petroleum stocks. Type of operation (taxi, courier, commuter, etc.) appeared to have some effect on viscosity thickening. Gasoline engines were generally more severe in terms of viscosity increase than diesel engines. Mileage required to go out of grade increased with increasing low temperature viscosity. It seemed that oil viscosity increased at a more rapid rate when measured at lower temperature. The investigation quantifies the amount of viscosity increase for typical passenger car service but provides no data to confirm effects of viscosity increase on startability in the field. Field testing is planned to explore startability. Supporting test data are appended.