Well when it rains it pours I just finished relatively cheap repairs(new belt, thermostat, turned rotors, new tires) and everything was good.

About 2 days later my low coolant light came on. So I drove it back to GM and they filled it, figuring there might have been a bubble and to watch it. 4 days later same light comes on but when you check the level cold the rad is full. So I decide to pull the cap and run at idle to flush out what must be a monster bubble. The level drops about 8" and is just polluted with what looks like rust. Last flush was about 1 month prior, all new dexcool too. Anyway it starts to rise and rise and just starts pissing out like its being pushes from the bottom. Engine starts to overheat so I kill the ignition.

Went to GM for some dexcool to get me from home to the shop safely and bring it to them. Hoping its somehow related to the thermostat replcement they put it up looking for coolant leaks, blocks whatever... nothing. Shop foreman got called over and diaged it as exhaust gas in the coolant presumable from a blown gasket best case. Otherwise cracked head or block.

Either way it looks like what is happening is exhaust is entering the coolant system, pushing coolant into the overflow and then exiting at the cap since it has more than enough pressure to list it. You can see the level drop, and with the cap definitely has gas exiting it, easily visible to eye. So what you guys think? Head gasket? Could changing thermostat have any chance of doing this? Let me know soon, car is going to be torn apart today to inspect heads unless we can think of something simpler that could cause this.

 

Did you get this fixed?

 

Interesting. Did you use the right (reverse flow stat?) Rust color is normal with dexcool. Low coolant lights are par for the course with these cars.

So if the system is full, radiator, block, reserve container, etc. and you have the correct stat in there, and it still overheats, I'd say you have a problem.

But if it is just the low-coolant light, and rusty coolant, it may be too premature to tear it down.

I do believe that if run the engine with the cap off that you are going to get coolant coming out the radiator.

Just do some more analysis before you assume something major is wrong. And don't pay too much attention to mechanics until you have completed your own analysis.

On the other hand do not run the engine into the overheat zone or you WILL have problems.JMHO