An engine cooling system includes a liquid-to-air heat exchanger having an associated fan and a pump forcing convection and a controller communicating with the fan and the pump, the controller increasing fan speed in response to a first gradient in heat transfer rate to power exceeding a second gradient in heat transfer rate to power for increasing pump speed, and increasing pump speed when the second gradient is greater than the first gradient. The controller may increase the pump speed in response to a desired increase in heat transfer rate. The first gradient may be based on a gradient in heat transfer rate to air flow from a map of heat exchanger performance. The second gradient may be based on a gradient in heat transfer rate to coolant from a map of heat exchanger performance.