Why does my electric radiator fan turn on?

The cooling fans are designed to turn on at a predetermined coolant temperature or if the AC/Defrost is turned on. However I would check for proper thermostat operation, I just got done replacing a thermostat in a vehicle that wasn’t closing all the way so it was taking way too long for the engine to get to operational temperature. Yours maybe also be leaking by just enough to make the gauge read low for a long time due to the coolant flowing even when cold. A live data scan will show the engine coolant temperature at the ECT sensor and not the gauge sender so you will see what the computer is reading. If it is indeed too cold then a thermostat replacement is needed.

I'll try not to give you nonsense. If the temp gauge on your car is actually working properly, I would say your cooling system thermostat will needs to be replaced. Putting cardboard in front of the radiator is a band aid to heat up the cooling system. Replace the thermostat first and make sure you have no coolant leaks from any hoses or the radiator itself. You can perform a pressure test to verify. Make sure the coolant is filled properly and you have no air in the system. Once the Car is reaching the proper operating temps, you can then see how the fan reacts. Driving a car without being too cold uses more fuel and the car will run rich.

I agree, plus I have a 2008 Grand Marquis (same car). Your normal operating temperature is 195°F which will put the temperature gauge at exactly the halfway point. Putting cardboard in front of the radiator is a bad idea. Restricting the airflow in the engine compartment will, among other things, burn out the radiator cooling fans! If you service the cooling system it MUST be refilled by adding coolant directly to the engine through the thermostat hole. If you don't, you will have air trapped in the cooling system! Replace the thermostat and you'll be fine. Hope that helps! Jim