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Every time I turn my heater on with the rear defroster at the same time, my temperature guage goes all the way down pass the cold position (It also has happened when I only use the ac or heater) and then my heater will start blowing out cooler air... and if I switch it to the ac, It stays at the same temperature.. Then once I turn the car off, the fans keep running for about 5-10 minutes and if I drive it like that for a long period of time, the check engine light comes on and the codes says that the engine is running hot... if i disconnect the positive battery for a few, everything goes back to normal including the fans and the guage until I mess with the heater and defroster. I have drove the car for over three weeks without messing with the heater or anything and nothing went wrong but yesterday I turned it on and about 10 minutes later the guage slowly went down.. I also replaced the cooling sensor a few weeks ago
Thanks... You just reminded me... The coolant light comes on now too. And it stays on no matter what
 

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temp gauge problems

I just phoned Steve Overbeck who is a top notch mechanic and also has a Sat. Morn. radio show on WDJO 1160 am radio. I have the same problem with my Chev (the car from hell) and he told me it is most likely the thermostat. Also there could be an air pocket forming that prevents the gauge from registering. His advice is: change the thermostat, flush the system and when refilling be sure to bleed the system to remove any air. Also, be sure to get your thermostat from a chevy dealer as parts houses do not carry the quality that is needed and it is too expensive to get a defective thermostat and have to do it all over again. First thing though, bleed your system and this alone might work. bleeders are on top of the motor and real easy to get to. Hope this helps you out!
 

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Have this same thing happening with my Impala.
I read through some pages said it was probably the temp-sensor. So I replaced it. However, during the replacement I really messed things up. I overtightened the sensor and cracked the lower intake manifold. That $15 part ended up costing me $750!

What's worse - it didn't fix the problem! I still have the intermittant temp gauge problem. Whenever the gauge is not working the AC will not work and the fans will continue to run. Another trip to the service center and they diagnosed it as a bad thermostat. Unfortunatly they have to tear down almost as far to replace that as they did to replace the intake manifold! Just haven't been able to gather the $$ for that yet :(
 

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ummm the t-stat is about a 1 hour fix, including the bleeding of the system, its right on top of the LIM and you only need to remove 2 10mm bolts plus the upper rad hose... thats it! How much did you crank down on the LIM? It doesnt seem right to have cracked it by just tightening it down, chances are it was already cracked. BTW there are torque specs for the LIM, including an order you have to go in for it to seat properly...
 

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having the same issues with a 2001 Impala 3800

Had the low coolant light about six months ago. Check the level always good.
Never changed the low coolant sensor till about 2 weeks ago.

Before I changed About 2 weeks ago the Temp guage starting going to zero and the AC stops and the fans come on low whe nthe key is off for about 3 minutes.

I changed the the low coolant sensor. It kept the low coolant light off for about 2 weeks.
Now the temp guage and AC is acting up almost every day. I bought a t-stat and temp sensor. Will cahnge them both and add new dex cool.
I'll post back results.

Car has 120k miles.
 

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Just a follow up. Did replace the t-stat and temp sender. All has been good. Ac and temp guage working.
I still get a low coolant light every other day or so. Replaced that sensor about 2 weeks prior to this task.
I have read to purchase a true GM sensor vs. autozone(I bought mine here).

The temp sender in the intake was somewhat a pita.....Not much room to get a socket on. I had to use a box wrench and not much area for tighening.

Now on to fixing hte drvrs pwr window button....Wearing out. working intermittely.
 
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