I have a related question:
I own a 2000 Ford Focus ZX3 Kona Edition, 5 speed manual transmission, 30000 miles on the odometer, and other than squeeling brakes when cold, she was running fine. A few days ago I took her for the 30000 mile service, and they replaced the front brake- pads and rotors (no more squeeling when cold).
I picked the car up, and while driving home that night I noticed that at highway speeds the car would overheat to just under the redline. At normal surface street speeds the temperature would be normal, until I stopped, then it would spike high for a minute before returning to normal. When idling or stuck in traffic I can hear that the radiator fan is on. Prior to the service the temperature was constant at the ½ mark and the radiator fan would only come on when it is really hot.
I returned my car to the dealer, and they said the cause was the thermostat being stuck closed, and I was charged for the thermostat replacement. When I asked them how this happened, they it may have been caused by the cooling system flush that was performed during the 30000 service.
While driving home that night I noticed the temperature was a little below the normal ½ mark, and although she did not overheat immediately, after about 30 minutes of highway driving the temperature would spike to ¾ mark and then after a few minutes recover to below ½ mark. This spiking behavior would continue happening at highway speeds, especially during hard acceleration or hill climbing, and as before when stopping. When stuck in traffic or stopping I could also hear the radiator fan blowing. Symptoms very similar to the original problem, except the overheating was not as dramatic.
I returned my car to the dealer, and they said they could not find anything wrong, neither could they reproduce my described behavior. I was not charged for this check, and was told to return the car if it happens again. Well, it still happens.
From posts in other forums I have been advised that it may be a leaking thermostat housing, or a faulty temperature relay.
I would appreciate your opinions on what the cause may be, or online references to similar cases that may help me when I take her back to the service department.
Regards
Pieter | 
