I have a 2003 3.4 monte.my temp gauge goes to overheating and back down.the sensor was replaced but did not solve the problem.i do not see any problem,the oil looks good,no oil in the anti freeze,thermostate seems to be opening.any ideas

 

its just your gauge then? when does it occur?

 

I will start driving and it will be fine. But soon the temp gauge will be at max. Then about thirty seconds later it will drop back down to either 1/4 or 1/2. And the whole time this is going on, I don't have any heat. If it drops down to 1/4 I might have heat for around 10 seconds but it quickly goes away. It seems completely random to when it is going to overheat because I can be driving for 40 mins and it will happen twice, or I can be driving for 15 mins and it happens three times.

 

Also I lose a little bit of antifreeze every 20 or 30 miles. There is no antifreeze in the oil, or any oil in the antifreeze.

 

well first off if ur losing coolant that would b the problem to start with...u havent been able to find the coolant leak?

 

I just had to replace the water pump in my 3.8 2005 LT. It sprung a leak, causing overheating. Maybe start there?

 

coolant elbows? also check around water pump. run your hand under the water pump and if you feel something wet, your problem solve. i think it's more likely the coolant elbows cause it's very common they leak.

 

Go to AutoZone and they'll let you use a Cooling System Pressure Tester ... just leave a Credit Card or your Registration and its free. No charge. Pressure test that cooling system and locate the leak.
If its someplace bad and looks like its going to cost big dough to fix ... call Chevy and get it vouchered under the Dex Cool Settlement.
If its something like a clamp or an easy fix ... get after it and your problem is solved.

 

I read where the Dex Cool reinbursment deadline was Oct.27, 08

 

This isn't an answer to this problem but I am having the same issue. the only differance is I am not losing any fluid and have replaced the water pump and thermastat bled the lines. other than that it is the same problem. When my heat kick on the problem goes away (260-160) in a flash.