I own a 2002 ss monte. I was driving up a small grade when I saw the water temp getting hot. The "Hot coolant light came on and the motor stalled. I had some water in my car, so I let things cool off for a few minutes added water and drove about anoyher mile to a gas station, where I waited about an hour for things to cool down and fill it up with water. I then drove home about 20 more miles and watched the water temp get hot again but not to hot to have the "hot coolant" come on. I replaced the radiator that had a crack in one of the tanks and ever since it has a rough idle. Put in new ac/delco plugs and bosch wires. The car runs much better but I can't get rid of the rough idle. I replaced the coil packs, no help.

 

Still having heat issues? Wouldn't be surprised if you cooked the engine if you left it get that hot!

 

You need to find the source of the hot reading. It could be bad head gaskets forcing combustion gases into the cooling system for example.

The fact the car stalled is not good. That concerns me when coupled with hot temp readings.

 

Yes, you could have fried the engine or blown one or both of the head gaskets. BUT, check your intake gaskets first. These engines are notorious for the pink antifreeze eating up the intake gaskets. If your gasket was weakened then when it got hot it could've made a tiny hole in it and caused a vacuum leak. A small vacuum leak from the intake would cause your car to idle erratically but seem to run ok when you give it the gas. It may sound crazy but it's worth a shot to check those intake gaskets. All these newer GM v6's with the pink antifreeze is really bad about blowing intake gaskets. Your intake has air/fuel mix and antifreeze running through it at the same time. The only thing separating the two are the intake gaskets. If the gaskets are bad and it still runs it gives the antifreeze an opportunity to get in your cylinders. That's probably gonna be hard on your engine the longer you run it.

 

A way to check for vacuum leaks is to have your car idling and spray starting fluid around your intake and where it bolts to the engine. You can lightly spray the vacuum lines and where they hook up too. If it has a leak, the starting fluid will make the engine increase in RPM's. By the way, you posted in the 78-88 Montes lol.

 

So you changed your radiator and now you have a heat problem coupled with a rough idle? When you filled the new radiator did you bleed the system? At least 2 times. I have found that in the 3800 motor there are lots of pockets for air to hide.
When the engine is hot and you turn it off do you hear bubbling from the engine?
It's been my experience that when air gets into the cooling system the engine will run at a Higher than expected idle, anywhere from 1500 to 3000 tomorrow.once you've properly bleed and filled the system your car runs fine.
I Also agree with the others hear, if you ran the car until it stalled there is a possibility of a blown Head gasket upper or lower intake gaskets or all of the above.

 

I've discussed this in length. DEX cool was re-formulated in the mid to late 90's (as a result of GM loosing a lawsuit blaming DEX for LIM gasket failure). The LIM gaskets fail at 100K-150K because nylon was garbage to use for a gasket. GM had LIM gasket failures with cars that NEVER had a drop of DEX cool (such as my old '94 Grand Am). The nylon cannot handle the pressure and heat from any coolant for that many miles.

I don't recall the exact year DEX was reformulated, but the 2000+ Monte is definitely in the clear with the updated DEX.

This is why companies like FelPro now have aluminum LIM gaskets, they are far more reliable.

It is possible that the LIM on these cars can fail allowing coolant into the air chambers going to the cylinders. But most the time, the LIMs fail, coolant drips down into the crank case and mixes with the oil (still not good) or is pushed out of the engine together.

If you suspect a coolant leak, get a radiator pressure tester from the parts store (loan-a-tool). Bump the pressure to about 13lbs on a cold engine, look and listen for leaks. To get coolant in the air flow, leading to the cylinder, it's more common for the EGR stove pipe part of the nylon UIM to fail and allow coolant coming to and from the throttle body to bleed into the main chamber of the UIM.

It concerns me the car stalled and you had high temps. Did it stall because it overheated and if an overheat stalled it, what other fall out do you have? As wvmontels mentioned, was coolant leaking into the incoming air and hydro-locking-like situation the car (which could also give a rough idle)? A couple big questions that need answers.

 

After I changed the radiator I had no more heating probs. The crack in the side tank let the coolant get out. Funny thing is that after I changed the plugs and wires the car has as much power as when it was new. It now has 195,000 on it. I had the cat clog up at 85 ,000 miles and the dealer replaced it at no charge but they charged me 800 bucks for a new intake manifold. When the cat got hot it did the same thing only it had now power. Car runs as good as new except in drive or reverse at an idle. I'm going to check for vacuum leaks. If I cooked a head gasket I should have a miss under hard acceleration, I'm thinking.Lastly I had a rebuilt tranny put in 7.000 miles ago for 3100 bucks. No coolant in the oil.

 

It could be those Bosch wires also starting to fail.
Possibly a dirty MAF...
Or a dirty TPS...(it too needs to be cleaned with higher mileage motors) periodically....

 

Not exactly. I've had a car that the only time it ran "bad" performance wise from a failing head gasket was a little rough idle on a cold start. This was because when the car was off, the pressure from the cooling system relieved some anti-freeze into a cylinder or two and that anti-freeze had to burn off before it would run fine. After that, it ran with no miss or hesitation. But the cooling system was getting over pressurized from combustion gases. It got so bad, it blew out the gasket on the side tank of the radiator and my temp gauge readings were out of control.
Once I found out what it was and changed the head gaskets, no more problems. I drove it another couple of years and sold it last October with 215,000 miles. The guy who has it now uses it as a winter beater and has put zero into it, just gas and oil changes.