Quote Originally Posted by Identity_Crisis
People put cardboard over half the radiator when they have an upgraded cooling system and the car won't get up to operating temp in cooler weather. It won't help gas mileage any.
If an upgraded cooling system is keeping the engine below operating temperature, something is wrong- most likely the thermostat. You could have a giant radiator and giant radiator fans, but the thermostat only circulates coolant through it when the engine needs to be cooled.