What's causing car to overheat??
 

So my 2002 GT begins to overheat after driving for some time on the road WITHOUT turning on the AC. This happened first a few weeks ago and I had the AC on that time. So after that I've been rolling with no AC. But then last night it started to overheat again after driving for about 20 mins. What's the problem? I have coolant in there I check it every week. This happened last year when I noticed my AC wasn't blowing cold air when I was at complete stops. Turns out my cooling fan fuse was out, I replaced it and drained my coolant and put fresh new antifreeze in there and that fixed the problem for about a year. Now it's happening again but it's not the fan this time because I checked. So what else could it be? Keep in mind that I live in Texas and it's been in the triple digits out here for about a month straight. Could that have anything to do with it. Thanks in advance.

How do you know its overheating? are you going off the stock guage because its not exactly accurate. Is it overheating in town/while idling or out on the open road and highway? If its overheating while on the highway I would think its a airflow problem and your radiator and or condensor is full of bugs or your radiator itself is clogged up.

I know its over heating because the gauge goes up and I could smell the coolant leaking out from under the cap. I pulled over and yea you can see all the water boiling out all under the car. And It overheated a few weeks ago while on the freeway with AC. Last night I was on the busy streets stopping and going with no AC. I let it sit for a day and I turned it on and let it idle for about 15 mins with the AC full blast and it didnt overheat. Seems like it gets hot only when it wants to.

you might need a thermostat..i would start with that its cheap an simple...also could be a bad water pump

Is the weep hole on the water pump leaking? Check the oil and looks for signs of coolant mixed with it and vice versa with the coolant.

If your coolant level is fine and the fluid itself looks a normal neon green as it should (as opposed to a brownish tint that would occur if your head gasket was failing and oil was mixing with coolant) then replace the thermostat, as was mentioned. If that doesn't fix it, then it might be the pump or a corroded radiator or something. Either way, this isn't something to screw around with. you are going to ruin your engine. I'm a little confused why you keep driving the car and continue wondering why it's overheating on occassion. I'm not trying to be rude, but you're going to ruin the motor if you don't get it solved pretty quick.

As others have said, replace the thermostat as it's an inexpensive thing to do. If that doesn't do it then pull the water pump and see what it looks like--if the pump is OK then it is most likely that the radiator is partially clogged. This is common on older cars that have not had the coolant changed regularly.

A radiator shop can flow test it, however as you can get a replacement for $150 or so having it flow tested may not be worth the cost...