Odd overheating problem!, Hoping for help from you gurus Options

[wilc4]

I have a 1996 GT Convertible. Runs absolutely fine, except on occasion (it has happened about three times in the last month) I look down and the temperature gauge is well higher than it usually is at. Usually it is stuck - like a rock - a little under halfway up the gauge. When it does this, I look down it is probably 60-70% up the gauge. All three times it has done this I have been stuck in traffic stopped with the A/C on.

Now, here is the weird part. I turn on the heater and immediately goes back to normal (which isn't a surprise since it adds in the extra heater radiator) but then I can immediately turn the heater off, turn back on the A/C and it is fine. Last time it did this I popped the hood prior to putting the heater on and the fan was going full speed, so that isn't it. Also, I let it sit for a while and the gauge didn't seem to be moving towards overheating - but was just running hotter than usually (within the normal range, but certainly abnormal considering the temperature in this thing has never previously gone over its usual spot)

My guess is that it is a failing thermostat and that somehow putting the heater on gets it to fully open and then things are normal. What do you all think? Any other ideas?

[Jamchell]

I'd go with that, install a thermostat and see if it clears up the problem. It really sounds like a sticking stat to me. I'd do it soon, as it will most likely fail and leave you stranded.


Only other likely thing would be a partially plugged radiator. Something to think about if the new stat doesn't fix it.

[Bitter]

it could also be a wonky gauge or sender, you need to (next time it happens) measure the actual coolant temperature somehow. grab one of those cheapy non contact thermometers and shoot it at the thermostat housing. your coolant can be upto 220-230F and you're not overheating. 240 and up is overheating.

[wilc4]

Thanks that is some good help. I will probably get the cheap thermometer (would be good to have anyways) and also change the stat. Since it got hot I should change the stat anyways...plus, they are like $10 and easy to get to...

[Bitter]

while you have the coolant drained (you should drain it) replace the upper and lower radiator hoses, they're 13 freaking years old!

remember to run the car until the fans come on with the radiator cap off, adding coolant as it warms up (after the initial filling) and while checking the temp gauge. also make sure the temp knob is turned all the way to HOT and that the heat does work in the car.

[cloqwise]

Why don't you run it without a thermostat for a while and see what happens, will take longer to warm up but see if it over heats then. Also when you get the thermostat out check it to see if it works by putting it in some boiling water and see what happens, or heat it up in a pan on the cooker and see if it opens then u will know if its the stat.

[Bitter]

running without a t-stat can actually CAUSE overheating. the t-stat slows down the flow of coolant through the radiator so that it can drop more heat before coming back to the engine.

[cloqwise]

running without a t-stat can actually CAUSE overheating. the t-stat slows down the flow of coolant through the radiator so that it can drop more heat before coming back to the engine.

Ah right, well i did this on my car and worked fine, took ages to warm up and everytime you got up to motorway speeds the temperature dropped quite a bit

[Bitter]

sitting in traffic it can cause problems.

[Jamchell]

Another big problem with running no stat on an OBD car, is you will run your fuel system in open loop most of the time. This causes your car to run rich, which will make for sluggish performance and increased fuel consumption along with increasing carbon build-up in your engine.