Effect of Engine Oil Viscosity on Low-Temperature Cranking, Starting, and Fuel Economy

The effect of engine oil viscosity on low-temperature cranking, starting, and vehicle fuel economy at low ambient temperatures was determined for vehicles equipped with four- and eight-cylinder engines. Oils ranging in SAE viscosity grade from 5W-20 to 30 were investigated at temperatures between -40 and -12°C.

For both vehicles, engine cranking speed increased with decreasing Cold Cranking Simulator (CCS) viscosity. This was reflected in easier starting with lower viscosity oils. In addition, the maximum viscosity for successful engine starting decreased as the temperature decreased. Fuel economy during engine warm-up increased with decreasing CCS viscosity, with the friction-modified oils investigated providing better fuel economy during warm-up and easier low-temperature starting.