overheating without overheating, er, boilover

Took the mustang for a spin today because it is the first time the sun has been out in 2 weeks. Took a ride around town for about 1/2 hour, maybe an hour. Got home, pulled in the garage, and poped the hood to let some hot air out (the temp guage wasnt reading hot, about 1/4 of the way up, maybe a little more, which is where it normally is at) it was about 80* outside, maybe 85, but I didn't have the air on. Anyway, when I poped the hood I see antifreeze all in the top of the rad in the groove around the edge, coming from the cap area. Put the car in neutral, rolled her out of the garage into the driveway, and hosed it off. First I checked my overflow tank which had a small amount in the bottom, but not much. After it cooled a little I checked some more. I pressure tested the 13# cap and it was fine. The overflow hose was clear, but it may have leaked where it meets the rad. Also, the rad was still full, so I didn't loose much. I'm thinking I'll put one of those spring clamps around the overflow hose to hold it to the tank tight, shouldn't be strong enough to crush the brass tube. I checked the hose and it's clear. Maybe I'll replace the hose while I'm at it. Any ideas at what this could be? The 302 dosn't overheat, but it liked to run with the water in the tank a little low, which is why I put the overflow tank on, and I havn't had a problem until now. Still didn't overheat (i don't think) so I don't think it's the thermostat. Any ideas? I'm gonna try that small spring clamp on the overflow hose first, but I don't see what else it could be. Thanks for the input

I had the same problem. For a few days I was smelling anti freeze and when I parked, it didn't overflow. Turned out to be a pin hole radiator leak, just enough to release the pressure so it wouldn't overflow. I'd do a pressure test on the radiator.

The hole was releasing the pressure, thus the cap wouldn't release into the overflow tank.

Where was the pinhole at? And if it had a pinhole to release pressure, why would it puke out the cap? I guess it still wouldn't be a bad idea to pressure test the system.

The real thing I don't get, I guess my real question, is why it puked out the cap and not into the tank?

Thanks for the reply [img]/phpBB/images/smiles/icon_smile.gif[/img]

<font size=-1>[ This Message was edited by: nickmobile67 on 8/13/03 9:50pm ]</font>

You may have a pinhole leak around the brazed on neck of the radiator making it look like the cap was leaking. Pressure test the radiator.

There is supposed to be a brass or rubber seal around the top of the cap to seal it off and one down in the throat of the fill neck for the pressure release. It sound like the pressure release went off and the top seal didn't hold. A new cap may be in order. I like to use a 14 lb cap with a pressure release lever. They have always worked great for me on the early Fords.
[addsig]

UPDATE

Today I finally had a chance to check it out again, and whaddaya know, the upper brass seal (not the pressure seal, the one above the spring) was cracked all along the one edge. I wish they made the repop caps with rubber seals, at least my extra stant will get me by for now though.