radiator overflow pipe bubbling

[htchbck]

This is on my '91 5-speed with rebuilt motor from my '93. I can drive the car for five minutes or a couple of hours, and it never overheats. But whenever I turn off the motor, the coolant overflow pipe is bubbling. The coolant itself never boils, and the pipe isn't sending water into the tank, just air. My coolant is never low and I've been driving the car like this for well over a week now and its running fine. It just bugs me cause I don't think it is supposed to do that. Any ideas as to whats happening?

[Festy46]

Try a new radiator cap. It's possible that when you shut off the engine, the water that is actually in the engine (not the water in the radiator) gets hotter because it isn't circulating. That water (in the engine block) may try to boil because there isn't enough pressure in the system. Another possibility is that you have a compression leak into you water jacket somewhere. Use a leak down test tool with the radiator full and watch for air bubbles coming up out of the water. Make sure you have the radiator filled to the neck.

[htchbck]

i bet its the cap, everything interal should be good since i rebuilt the motor about 3000 miles ago... I didn't even think about the cap letting off too much pressure though, thats probably it, its still got the original cap on it. I'll try a new one this afternoon.