Last night I noticed my car ran at an unusually high idle even though the engine was warm (1500 - 2000 rpm). I parked at a store and when I drove home later that evening I noticed a high temp spike while driving in slow traffic. I got on the open road and the temp went down to its normal level. When I got home I let it idle to see if the fan kicked on when it was supposed to (it did).

Today when I started the car I noticed the high idle again. This time I opened the hood for a peek. The coolant reservoir was about an inch above the "hot" line. The engine temp acted normal (when it got to 220, the fan turned on and cooled the block, then it shut off like it should.

After almost twenty minutes of high idling the engine finally got down to normal rpms, sputtered a bit, then stalled out. I noticed the hose going from the radiator to the intake and the coolant reservoir lead was VERY hot, but the radiator and the hose coming from the water pump was alot cooler (I could just about leave my hand on it). There should be a slight difference but I don't think its this much.

Any ideas on what the prob could be? My logic points me to a stuck thermostat.

Any info would be much appreciated!

 

I would check the thermostat. Take out the thermostat and drop it in a pot of boiling water. It should open up. If not it is bad.

Actually if it's a stock 195* t-stat it should start to open before the water boils.

 

I agree...seems like a slow stat or a partial opening stat...enough to keep it from totally overheating but not enough for normal operation..if that makes sense

 

I agree, probably the thermostat. Could also be too much coolant in the system, and not enough water. Coolant expands more than water (making for the higher level in the tank) and it doesn't actually COOL anything as well as water does, making for the hotter running temps.

 

There may indeed be a problem with the thermostat, but that doesn't explain the high idle. Even if the thermostat were stuck closed, the CTS is exposed to coolant at the intake crossover. Hotter coolant would tend to drop the target idle RPM even lower (if the programming is stock). Additionally, if the thermostat is sticking, the upper hose would be passing almost no coolant, and the fan running would lilkely have little cooling effect. Since it eventually cools down, that is less of a possibility. You can allow the engine to cool fully, remove the radiator cap, and monitor the level of the radiator tank to see of the coolant is actually moving. Once the thermostat is opened, a little blip of the throttle should cause a momentary drop in coolant level in the right side radiator tank.

 

leave it to vader....knowing more then us...lol...im not worthy

 

All,

Today I pulled the thermostat. When I tried to press on the spring it definitely felt "stuck". That is, I had to try several times in order to get it to press compared to the new one which pressed in evenly every time I tried.
Put a new one and all is well.

Vader,
I can't explain the high rpm's, but I certainly did see it happen. Here is a theory:

If I'm correct, the coolant temp sensor and the engine block temp sensor are independant of each other. The coolant temp sensor is on the top side of the manifold while the other is actually in the block. I think if the coolant temp sensor reads "hot" it would actually increase rpms which would circulate more coolant through the block to the radiator. Normal driving would cool the radiator and the fan would kick in when the other sensor passed its threshold. Like I said, when I was working on the car last night the lower hose was cool enough for me to keep my hand on it after the engine ran for twenty minutes. The upper hose was very hot and since it connects to the thermostat and intake manifold where the coolant temp sensor resides. Another thing is the fan actually blows air on the front/lower part of the engine block. Thus the lower part where the engine temp guage would become cooler faster than the coolant temp sensor since no air blows on the intake manifold.

Hopefully, my problem is solved. Thanks for everyone's help.

Thirdgen 4ever!

 

BTW - after installing the new T-stat and driving around, BOTH hoses were hot (roughly the same).