Hope somebody has some ideas for what this could be..
I own a 2002 monte carlo LS. For the past couple days the car has been overheating almost instantly from ignition. goes straight to the red marks and the inside light turns on to say "HOT COOLANT TEMP" Ive changed the thermostat and that hasnt worked and now am wondering what else it could be..
Ive added coolant to both the reservoir and the radiator but it hasnt done anything. Any other suggestions would be greatly appreciated. Thanks!

 

Water pump

 

Could be a water pump, on a simple note.

But also could be your head gasket/ LIM gasket, the 3400 is known for both of those gaskets failing.

 

I looked at it some more and found that the little problem was that there was air in the hoses. i fixed that and its running fine now but the LIM is messed up too. Thank you everyone

 

Now that boggles the mind wit me because I have a 3800 engine and I wonder how to take the air out the hose?

Mines overheat as well, which I have chance the radiator (brand new), thermostat, radiator cap and did a complete coolant flush. Still, the needle does not stay in the middle. Hell I can't even use the AC because more than likely it will ATTEMPT to overheat.

 

rgant_19, the 3800 engine is also known to have a leaking LIM gasket. Its possible that you have a leaking LIM.

Also, on the 3800, to bleed the air out of the system, you loosen the nut at the top of the thermostat housing. When nothing but pure coolant comes out for a few seconds, you have bleed all the air out of the system.

 

I sure hope not mamonte. I will bleed it today and see. I just drop my wife off at work this morning so the car didn't overheat today but, it did go one notch pass the middle line and indicating that I have low coolant (with the dashboard light)...

 

I am not trying to be negative, but realistically, it really sounds like that is your problem, especially if you are loosing coolant.

Start by topping off your coolant, and bleeding the air in the system. Then make a note as to where the coolant level is once you are done topping off, and bleeding the system. Keep a close eye on the level. If you notice that you are loosing coolant, then I think there is a very good chance you have a leaking LIM gasket. Especially considering all the cooling system work you've recently done, only thing left really is the LIM gasket. Like I said, its very very common on the 3800.

Good Luck!