Rheology of multigrade engine oils

Abstract

Rheology of multigrade engine oils, SAE 15W-40, SAE 20W-40, SAE 20W-50 and SAE 25W-50 has been examined experimentally in the temperature range of -20 to 20°C. Experiments have been carried out to observe the dependence of shear rate, time and temperature on the apparent viscosity of these multigrade engine oils. The oils SAE 15W-40 and SAE 20W-40 are found to behave as Newtonian fluids above a temperature of about 5°C. The oils SAE 20W-50 and SAE 25W-50 are found to behave as Newtonian fluids above a temperature of about 10°C. Below these temperatures, they behave as dilatant fluids. These oils also exhibit a rheopectic behaviour. The apparent viscosity of these multigrade engine oils decreases with increase in temperature.