engine coolant leaking?

I have a 99 Alero and the engine coolant light comes on and goes off while driving. I made a mistake and filled it the first time with some regular Prestone antifreeze. This weekend my car got into the hot zone and I immediatley pulled over and waited for it to cool down again. We added water to it and took got the radiator flushed and refilled with Dex-Cool the next day. The light still came on and the level was low again. I added about 3/4 of a gallon of water and started my car. We didn't see any leaks or puddles underneath the car and all of a sudden a hug gush come out. We were thinking it was the overflow tank?

I still drove it to work today and the light was on more than it was off but it was running in the middle of hot and cold. We couldn't see any leaks of the hoses or any bubbling of the heads. Any suggestions? I heard that it could be the radiator cap since it is broken. The cap screws off but there is no spring and the bottom part gets stuck in the overflow tank. Could this be it? Help.

Sounds like your radiator/overflow tank cap is bad. Unscrewing the cap should remove the entire unit. I had a similar problem a couple months back. The cap broke when I went to remove it to add some coolant to the overflow tank. About $8 at Autozone, and a hammer and chisel to remove the part that was stuck in the tank and the problem was solved.

Gotta love cheap plastic parts.