Overheating???

I have a 2001 Pontiac Montana that we purchased used about a week and a half ago. It seemed to be in excellent shape (interior/exterior perfect and all "options" working) and ran like a dream until yesterday.

So yesterday it started to overheat. The temp would go up between the 1/2 and 3/4 mark (not quite in the red zone) and would waiver there for a bit and then go down some (when idling, like in a drive through lane or at an extended red light). It would then go down to between 1/4 and 1/2 mark once I took off and was driving for a bit. My husband looked at it when I got home and there was water coming out of the water pump. So he went and bought a new one and replaced it. We thought that would fix it but this morning on my drive to work, it started doing the same thing.

Any other ideas about what might be wrong. We don't have any of the telltale signs of a blown head gasket...no water in oil, oil in water, white smoke or water from tailpipe, milky ring around oil cap or milky look to oil...none of that. So I'm thinking maybe it's the thermostat or maybe air pockets. Any ideas would be greatly appreciated!!!

This is what I get for buying used instead of new and without a warranty at that!

As you probably know from reading this forum, the engine on the Montana has an infamous history of problems with the lower intake manifold gasket. However, you mentioned some of the telltale signs (coolant in oil, goo on the oil cap) and said you don't have those. That's good, assuming the seller didn't disguise the problem by changing the oil and cleaning the gooey cap.

If it isn't the intake manifold gasket, then you are probably right on with something like a thermostat, radiator cap or air in the system.

Keep us posted.

If you do change the thermostat, be prepared. It's not a quick job. You have to remove a lot of stuff to get to it. You will become intimately familiar with a bunch of stuff on the top right side of your engine.