Pump throttling at light engine loads can reduce the heat-transfer coefficients in both the water jacket and the radiator, reducing HC emissions and friction/heat-transfer losses. Pump throttling can also accelerates engine warm-up. Pump driving power under pump throttling is predicted using measured flow parameters of a production-engine cooling system. The lower pump driving power due to pump throttling results in a 0.5% decrease in predicted BSFC. Engine BSFC can decrease by more than 0.5% due to reduced friction and heat-transfer losses as a result of the increased engine temperature.