I hear this an awful lot about higher milage Zetecs. I am not sure what causes it, but it is either that the temp gauge gets out of calibration (or bad temp gauge sensor) or that the engine coolant sensor that controls when the fans come on is bad. Another thing to do is clean the exterior of your radiator. Although you might not have major obstructions, little things like dirt and bugs accumulate and block aiflow over time, especially if you do alot of night driving. I think the best way to do this is to squirt forcefully between the fins to get the crud out, but be careful not to bend them or cut yourself. If you are really devoted you can go to a supply store and get some condensor coil cleaner and spray that on and then rinse out the coils. That would do a really good job. Zetecs aren't known for waterpump failures and even if it did, it would overheat quickly without cooling down. I believe your problem rests with the sensors or maybe a little with the plugged radiator. Good luck!
