Abstract: A method of cooling a locomotive engine wherein the temperature of the coolant flowing into the engine is controlled in response to the temperature of the lube oil flowing out of the engine so that the difference between these two temperatures is limited to a predetermined value in order to limit the differential expansion between parts within the engine. The predetermined value may be a function of the lube oil temperature, and it may have an absolute maximum value. In the event that the temperature difference exceeds a predetermined value, the power output of the engine may be reduced as a function of the length of time that the temperature difference limit has been exceeded. The rate of change in coolant temperature may be limited during periods of decreasing lube oil temperature in order to limit the duty cycle demand on coolant system components.