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I have a 1999 Pontiac Montana with about 110,000 miles on it. Recently it was overheating and I determined that it was because the thermostat. I replaced the thermostat and ever since then it will not get up to temp. the temp gauge in the dash hovers slightly above 100 when driving. If I stop and let it idle it will rise a little bit more but it drops back down as soon as I start moving again. Inside the car the blower blower cold to slightly warm air but that’s about it. I was told that the thermostat would fail “open” so I feel like it was faulty but i figured i would check because changing the thermostat means taking out the air intake system to get to it. it also seem s to be burning through(leaking maybe) coolant. there is something bubbling above where the thermostat was installed.
Thanks so much for any help you may give,
-Tony
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theres no guarantee that the thermostat will fail open.
unless you installed a motor rad thermostat. That said
check that your coolant is full and bleed the system for air.Theres a good chance that your lower intake manifold gaskets are leaking causing a loss of coolant. These engines are notorious for that. As far as not having heat, it sounds like you have air in the cooling system. The bleeder is located above the waterpump on a black pipe. It takes a 7mm wrench or socket to loosen. Make sure when you tighten it back down you don’t crank on it or it will break very easily. Just snug it up, it won’t leak.
I bled to system, it seems good, the car still will not get up to temp. I ran it after bleeding it for 20 minutes or so and still barely made it over 100 degrees.
Of course it’s only 6 degrees outside right now.
-Tony
The thermostat was whatever they gave me at autozone, I assumed (stupid I know) that they gave me the right one. If you mean to radiator fan then it don’t think it ever turns on, I will have my wife leave the car on when she gets home and see what’s going on with it. She has a 45 min drive, mostly highways, and it never gets above 100. I will let it run when she gets home so i know the engine is warm.
I could’t get the radiator cap off this morning before she left but the bleeder was shooting out coolant. again I will try to play around with it when she gets here and see what I can do.
Thanks,
-Tonynot a fan of auto zone.That said.If they gave you a fail safe
thermostat.its designed to go full open in an over heat condition.
If your cooling fans are not coming on.you may want to verify the
fans do actually work.If the car was driven.The car should come up
to temp.Two problems I’m seeing.is the thermostat correct? do the fans
work? If you have a advance auto.go the and get a stant.http://www.justanswer.com/pontiac/1o7az-replace-thermostat-1999-pontiac-montan.html
yes I got a fail safe termostat, I forgot what they called it. I am hit or miss with autozone, some people there are great and have helped a lot and some are worthless. I have an advance but it is a little more out of the way for me to get to.
so right when my wife came home(45 min drive) I went out and looked at it. the temp gauge was at 100 (the bottom of the scale) I played around with the radiator cap (stupidly with the car running) and figured out how to get it off
I don’t know if you have ever worked on one of these I assume most minivans are the same, everything is crammed in the engine compartment and there is a support bar right in front of the radiator cap. . . witch is angled into the car.
So… I got the cap off and, of course, fluid started shooting out all over the place. I noticed though that the fluid was a little warm at first and then cold after a couple seconds.
What I don’t understand is the temp gauge does work because if you idle when the car is warmed up it will go up a little and I can tell the engine isn’t overheating so where is all of the heat going? if it isn’t circulating because of a clog or something wouldn’t the engine overheat?
also the fan don’t turn on but they never need to. I can’t imagine it is just because it had been winter, there have been days that were fairly warm and still no overheating.
sorry if I rambled, just trying to give you as much info as possible,
Thanks again for the helpok. if the rad cap was removed and the coolant was only warm.
then you either still have air or the thermostat is stuck open.To me this screams air in the cooling system. Some systems are more difficult to bleed than others. I would suggest you try and bleed the system again. Use the info in the video. Don’t worry that you don’t have a bleeder valve as those just make filling the system easier. Do everything else the same however. Especially the part about turning the heater to hot with the blower off and running the engine at 2500rpm till the cooling fans cycle. You may have to do this a couple of times and let it sit between sessions with the radiator cap off. Keep us posted.
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