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What's wrong with my '97 Jetta's Cooling System?

This summer, on a hot rainy day, my 97 Jetta’s temperature gauge climbed to ~300F and the warning light came on. So I let the car cool, topped off the coolant (which was low) and went on my merry way.

It ran trouble-free for 4 months, (though during that time, it has consumed about 1 gallon of coolant)…until this past weekend. On a 250 mile trip, returning from Thanksgiving in Northern New York State. The weather was sleet/freezing rain, about 32 degrees. I had been driving for about 30min at 60mph. Suddenly my temp gauge climbed to ~300 and the warning light came on. Fluid level was OK. I let the car cool, started driving again. Everything fine for ~10 miles, then same thing happened. I also noticed that the intensity of the interior heat dropped to luke-warm just before the coolant temperature needle began climbing.

For the rest of the trip, the car overheated four more times. Sometimes it would run fine for more than an hour, other times it would overheat after just 10 or 15 minutes. But the overheating was always accompanied by a loss of interior heat. I eventually figured that I could sometimes stave off a climbing temp gauge (and get a return to normal running temperature) if I coasted for a minute and then carefully finnessed the level of acceleration.

I have searched all over the web, but much of the info out there seems to conflict. Does this sound like a sticky thermostat? Water pump? Air trapped in the cooling system? Clogged coolant lines? Please help. I can answer any other questions you have that may help to diagnose this problem.

Thanks,

Frank

It the car never overheated so severly (300F is severe) I would feel comfortable telling you that this is a symptom of air in the system.

Your car most likely has been damaged,you need to find out what caused the inital overheating situation and if any damage was done.

Cooling system pressure test, and test for the presence of exaust gases in the coolant is called for.

If these tests are good I would do a thermostat replacement (because it got so hot)

Perhaps it wasn’t exactly 300F. It is a little tough to estimate, because the temp gauge only shows where the 180F and 240F mark are. The rest of the ticks are unlabelled. In any case, I always pulled the car over immediately after the warning light came on. I am assuming that VW would not set the tempurature limits such that the warning light doesn’t come on until after damage has already occurred.

Presuming that there is air in the system, how would one go about removing it? This vehicle does not have a cap in the radiator.