Have the engine tested for a leaking head gasket. It involves drawing air from the radiator through a glass cylinder with two chambers filled with a special dark blue liquid. If combustion gases are present, the liquid will turn bright yellow. That air will prevent the thermostat from opening. They open in the presence of hot liquid, not hot air.

Answered by caradiodoc (expert)
17,256 answers provided

but in that case? wouldn't the hose that is going from the water pump to the radiator be full with water? because it only has air, I took that hose off after turning the car off and there was nothing but air? and the one that comes from the thermostat did have water, so i thought the thermostat does open...and why am I able to stop the fan with my hand even when the engine its hot?

Response from franxua1
8 questions asked

I wouldn't be concerned with where you find the air. The fact it's there is a problem and there's no place for it to come from other than a leaking head gasket. Don't knock yourself out looking for an elusive cause of the overheating until you eliminate the real common one.

Answered by caradiodoc (expert)
17,256 answers provided