if your fan isnt working properly, it could be as mentioned above. air bubbles.. most people dont realise, that a simple air bubble can keep your system from sunning correctly.. simply disconnect the upper rad hose from the radiator and fill with coolent til it comes out. put the hose back on the radiator, and burp it a few times (squeeze the hose). Remove the hose to make sure its still full. Then remove the overflow cap and run the car. you will have coolant boil out as air is being removed. that is the best way to make sure your coolant system does not have any bubbles in it.
works on all applications. the overflow is not the best place to fill your car with coolant, unless you are just topping it off.