My 2005 Monte Carlo is doin the same thing but one it's idles up the light says on until I cut the car off the the fan kicks on...I tried everything I have got new heads put on I got new radiator I changed thermostat I flushed radiator bleed the system and the car ran fine for about a week and went back to doin the same thing please help me figure dis out I have spent a lot of money on dis car

 

there should be a valve either on top of the thermostat housing (where the upper hose connects to the engine) or on a clyinder shaped pipe, standing vertically on the head in the front most part of the engine. your car may have both or one of these valves. the proper procedure is as follows- open the valve(s), pour coolant into the radiatior untill coolant is coming out of the valve(s). water shouldbe to the top of the radiator neck. close the valve(s) and the radiator cap. run vehicle and monitor temp. if the temp seems like it is going too high shut of the motor, and let it cool down. repeat procedure until system is full. this may take more than one attempt. these engines are so finicky about the air pockets, and it isnt hard to overheat one. use extreme cautions, as there could be steam at these valves and you could get burnt. one valve is a flathead screwdriver slot in it, the other is a 7mm. dont round off the hex on this one. it doesnt have to be very tight either. very easy to break the valve.

 

Some of the 3.4L cars have a plastic impeller on the water pump that's just pressed on. They are prone to cracking and then spinning on the water pump shaft. They still move some coolant but not enough to keep the temp down at idle. Replacement of the pump is the only fix.

 

No, mine is doing the same exact thing as yours. overheating at a red light. got it flushed about a month ago, still didnt stop, so its either the radiator or thermostat. No cracks or leaks. i have over 200,000 miles on it. im just not sure if its even worth putting more money into or if i should just invest into a new car...

 

I also keep coolant/ water in my car.