Would a stuck t-stat cause a service engine soon light? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 10-16-2004, 06:49 PM   #1
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Default Would a stuck t-stat cause a service engine soon light?

My temp gauge has been acting strange the last few days and now the service engine soon is on. Would a stuck t-stat cause this? or is it something else? by I mean acting strange is that when you start the car it stays at the bottom for like 5 minutes and then shoots up to normal temps and then shoots back down to the bottom again after driving awhile. If the t-stat was bad I know it would overheat but if it'* stuck open it wouldn't read temps accuarate. I checked the ECT and it seems fine, no shortings from what I can see but wouldn't that come up on diagnostic since it'* electrical?
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Old 10-16-2004, 07:00 PM   #2
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Well there are actually two sensors. One for the gauge and one for the computer. Funny huh? They're actually two different parts too so you can't swap them. I know when my engine was put back together one of them was left unhooked nad it did set the check engine light. Plugging it in fixed it. The car was only running for about 1min before this was checked and fixed so I'm not sure what effect it would have. So in any case, yes it will set the light.

How quickly does the gauge move? Is it gradual as if it could POSSIBLY be actual temperature changes or is it really quick?
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Old 10-16-2004, 07:12 PM   #3
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Quote:
Originally Posted by DrJay

How quickly does the gauge move? Is it gradual as if it could POSSIBLY be actual temperature changes or is it really quick?
It stays stuck at the bottom for about 5 minutes without moving at all. After about 5 minutes when driving it moves to the 200 range quickly. If I set in park and idle it will move alittle towards 220. Then when driving for awhile it will drop back to the bottom and stay at the bottom. It'* not nomal and it just started happening.
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Old 10-16-2004, 07:16 PM   #4
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Yeah that really sounds like a sensor problem. Just to make sure you don't have a freak problem next time it drops to the bottom (cold) pop the hood and grab the upper radiator hose, should be pretty hot. In anycase I think the sensors are rather cheap and fairly easy to get to. Might consider just replacing them both if you have some spare moolah. On a side note, if the one the computer listens to is failing also it should come along with a few warm-start issues. If thats not happening it may be safe to assume only the one to the gauge is failing, in which case I think its more of an annoyance than a problem..but I could be wrong.

edited cause I can't friggin type
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Old 10-16-2004, 07:30 PM   #5
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So you think it is my sensor and not a stuck t-stat? Why wouldn't the sensor come up on the codes if it messed up?
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Old 10-16-2004, 07:33 PM   #6
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The 'grab the hose' test I said earlier should determine if it is infact the sensor.
Also, its possible that the PCM doesn't listen to, nor care, about the sensor that the gauge is going off. Maybe it only cares about the one its listening to directly. I can't remember which of mine were disconnected, but it did set the check engine.
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Old 10-16-2004, 07:41 PM   #7
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The main thing I'm worried about is that the mechanice I took it to a few days ago said my waterpump sounds like it'* fixin to go out and if that does go out and my temp guage aint working right I could blow my engine or cause some serious problems due to overheating. I think I'm going to change the t-stat first just because it'* a easy and quick job and see if that fixes and it that don't then it must be a sensor. It probally still has the stock one in it anyways.
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Old 10-16-2004, 07:44 PM   #8
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Just my $0.02 FWIW, but I think the sudden change is caused by a stuck thermostat suddenly unsticking and opening quickly. I'd change that first and see what happens.
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Old 10-16-2004, 07:44 PM   #9
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Sure if you want, but like I said you can save yourself the time and money just by feeling around. Grab the top hose, bottom hose, and just generally feel around. See if it feels like 200deg or 100deg..Either way, hope it works out.
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Old 10-16-2004, 10:11 PM   #10
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A stuck t-stat won't throw a code. Simple reason being that there is no sensor directly attached to the t-stat.
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