Porsche Repair: heating problem, coolant, thermostat

Question
hi dave
i have a 1984 944 porche
i have no ploblems with it other then when istart it while running from cold i would say within 5-10 minutes it will overheat then the fans will kick on im talking the needle in dash will go to the red.there are no problems on highway just city.i heard it might be the sensor in the radiator. your comments wil be helpful.thanks rick

Answer
Rick,

You're describing a faulty thermostat.  What's happening is the thermostat is supposed to open as soon as the coolant (the water) in the engine reaches a bit more than operating temperature.  Since the thermostat isn't opening, the hot and getting hotter coolant cannot get to the radiator to cool down.  I'm not clear why the problem is not apparent on the highway.  Perhaps on the highway the average rpms is much lower than in the stop and go of city driving.

Dave