It seems like I've had this problem for the last week or so and the only time that I have a problem is on the way to work first thing in the morning, which is about a 2 mile drive. What happens is, I start the car up and let it idle for about 1-2 minutes, then leave for work. About half way to work, the temp will shoot up to about 215 degrees fairly quick, then I grip the wheel a little harder, hold my breath for a little while, and then all of the sudden, it'll shoot back down to about 170 degrees. First thing that came to mind was the stat was sticking and making it warm up so high so fast, and then when it finally unstuck, all the cold water from the radiator was cooling it down real quick since the water in the radiator would only be about 75 degrees from sitting all night. Yesterday I replaced the stat figuring that it would cure the problem but it didn't. I know the gauge is fairly accturate since the CTS in manifold confirms the temp swing. I can drive just about all day and night, and have no cooling problems whatso ever as long as the motor has some heat already in it. So I'm king baffled as to what would cause hot condition only once in the morning and then not be present any other time. Anyone have any suggestions?

Tom

 

Sounds like a typical POS Robertshaw thermostat to me. Your new one may very well be doing the same thing. Test the 'stat in a pan on the stove and you'll know if it is doing what you think it's doing.

 

Well this had been happening for about the last 3 or 4 weeks and then last Sunday my heater core went out. So I replaced the heater core and to my suprise the car has never heated up since. I would have never pegged it to be a heater core problem but it looks like it was.

Tom

 

how hard is it to replace the heater core? mine hasnt gone yet but i want to replace it before it does... im in the mood for alot of preventitive stuff for this winter.:lala:

 

Well I'm not sure your skill level, but I'd call it a moderate job. Not exactly easy for the first time, but not extremely hard. From the looks of things in there, it looked to me like it can actually leak a little bit into the box before it actually starts coming out onto the carpet which probably explains the subtle mystery coolant smell that I couldn't well where it was coming from. How many miles are on the car by the way?

Tom

 

If your worried about your skill level you can loop the inlet and outlets to the heater core together. That way your bypassing your heater core altogether. Then you have all the time in the world to replace it and you can still drive your car.