i have a 2000 chevy malibu (i know it sucks) i fixed the intake manifold gaskets (upper and lower) thermostat and its still leaking and sometimes overheating. my next thought is its the water pump. there's no crack in the radiator or hoses is there anything else that can cause it to overheat besides these. what about vacuum leakage? o2 sensors?
Have the system pressure checked that will show U where the leak is.
some other possible causes of overheat: lean mixture inadequate oiling poor circululation due to restriction in water lines
If you carefully squeeze or even feel some of the coolant hoses while the car is running then you will find out if the water pump is working. You should feel the coolant in the hose surging through the hose. You said it's still leaking coolant, but can't you see where it's coming from - then go from there? Are you getting any white smoke out the tailpipe - this would be a possible blown head gasket, a crack somewhere in the engine block or coolant water jackets. All of these would cause the coolant to seep into the combustion chamber and burn off, usually causing unmistakable white smoke (you see these cars on the road sometimes). I also agree with having a mechanic do a cooling system pressure check - this is the best way to tell where or if the coolant is leaking somewhere. They should also be able to diagnose the problem if its something else, and can easily tell if its the water pump too. Instead of wasting your own time and money, maybe its time to see a mechanic. I also like doing my own work, but sometimes you have to throw in the towel and let a reliable mechanic check it out. BTW, a vacuum leak would not cause overheating, but would cause bad idling, surging, bogging, etc. O2 sensors could cause similar problems, but again not an overheat. I hope I'm wrong, but you may have a blown head gasket.
