1998 Oldsmobile Cutlass Cooling Problem

Hello,

I have a 1998 Oldmobile Cutlass with a 3.1 liter engine 6 cyllinder.

A couple weeks ago my car overheated to the point where it actually boiled over, this happened I believe twice. Since then my dad and I have done several things to try and remedy the issue but havn't been successful. We first tried replacing the thermostat, this didnt seem to do anything because the car still ran too hot, it didnt overheat but it would run about 3/4 on the gauge. We then checked to make sure the fans were kicking in, which they were and we also tried bleeding the system. Its a strange car because theres only one bleeder on top and the bleeder thats normally on the bottom is supposed to bleed itself, which im guessing its working because you can hear air coming out of it when the car is too hot and starts to boil.

From there we tried flushing the radiator and engine / heater core thinking there might be a clog, the antifreeze that came out didnt have any oil in it and there wasnt any coolant in the oil either, so im hoping that its not a head gasket. We refilled the system after flushing it and it was a little better but still got hot.

Finally I was reading about how coolant will boil at a lower temperature if there isnt enough pressure or the radiator cap was bad. We replaced this which made a significant difference. The car was no longer getting as hot as it was and seemed to be fixed. However, ive now noticed that the car will run at normal temperatures for about 25 to 30 minutes and then it will slowly get hotter as time goes on, it goes from about 210 degrees up to 225, especially if I have the air condition on. But this is only after the car has already been running for about 30 minutes like I said. By the time I get home the car is now at about 235 degrees to 240, and when I shut the car off I can hear it start boiling and the temperature will rise a little more then finally cool off. Often times I will see a little bit of coolant that has eited the radiator cap but not much at all. Ive checked all the hoses and they appear to be fine, none have collapsed and now im at a loss as to what can be wrong.

Any help would be greatly appreciated. Thank you in advance.

Chris

PS: I thought about the possibility of the water pump being bad but when the car is running and we were testing it with the bleeder open it would push out antifreeze from the top bleeder when we rev'd the engine.