My 04 Monte has been overheating for a few weeks now, at first I could turn on the vent with the temp on hot and it would cool the engine down. Last week my upper coolant elbow busted so we replaced both, I was happy they finally made them aluminum!
We then did a flush over the weekend and the car stayed in the normal temp range with the flush in it and for about a day after we refilled the system. But when I would stop there would be what I think is a dripping sound.
When we refilled it we looked around and there was some fluid on the pulley under the water pump, should we replace it?
It's getting very hot now and when I turn the vent on only cold air blows.

 

Did you get all the little plastic pieces out? If the elbows deteriorated to a point where the broke up and you missed some or some fell in the engine it could damage or plug things. (Most likely water pump or heat pump) I don't know if the impeller blades are plastic or metal but this could have cause your problem.

 

Impeller blades are metal (either stamped or cast, but they are metal).

I agree with dbaldwin, make sure you got all the old elbow out (otherwise you might not have a good seal). You can get a radiator pressure tester (free loan a tool from most auto parts stores) and pressurize the system with the car off to inspect for leaks. Also, you want to make sure you bled the coolant system properly.

 

Good to know that they are metal. I spent a good 40 mins fishing for a small plastic piece from my engine (ended up blasting it out with the garden hose)