I have a 95 gt 5.0. last week I let the car idle for about 20 minutes and when I came back to it, the car was over heating and the coolant was gushing out the resivour and out of the radiator cap. I replaced the thermostat and the radiator cap and drove it down the highway (1 hour trip) with no problem. I got back to town, made one trip across town and it did it again. Fan is kicking on, so I figured it was a head gasket. I did a combustion gas test on the radiator and it passed; no combustion gas present. I am at a loss as to what this could be. Please help!

 

Could be the water pump. Also, you should do a leak down test to check your cylinders for leakage. If you have an internal engine issue such as a head gasket failure it will show in the leak down test.

 

Welcome to the forum, but just for future reference, these Tech questions should go in the Tech Section. Just to keep the forum organized.

You said the fan kicks on, which I'm assuming means someone put an electric fan on. Is it big enough to move enough air ? What's the radiator look like inside, clean or partially plugged ? Start the engine cold with the cap off, when the thermostat opens, can you see the coolant flowing ?

I doubt it would be a bad head gasket, as you have an iron block, with iron heads. Not that its not possible, but not as likely as aluminum heads.

I'd start a new thread in the 79-95 Tech section, and we'll get this figured out over there.