I noticed that the top tank of my rad was puffed out a bit, and was wet around the top seam. The cooling system was warm, not hot, but there was a good amount of pressure in the hoses. My first thought was head gasket, but then I thought that the Stant radiator cap should have allowed pressure to release before puffing the radiator, no? I just got the car out of winter sotrage but I doubt the coolant froze. I keep 50-50 mix in it, and it has been a very mild winter.
It's one of those caps with the pressure relief lever. When I lifted the lever, it seemed like I heard a "crack" as if the cap rubber seal might have been stuck to the radiator neck, causing it NOT to allow bleeding. Anyhow, there is no oil in the water or water in the oil that I can see.
Is it possible that a jammed radiator cap could cause a radiator to swell up? Â It seems to me that this is the only explanation. Â My mission now is to fine out IF the excess pressure came from normal heating-expansion with a stuck cap, or from a compression leak.Â