by Boost_4_Life » Tue Aug 27, 2013 8:56 pm
I had exactly this issue with my old supercustom. It would drive fine but when i parked up and turned it off it would bubble up and blow coolant out the overflow. I had the radiator pressure checked and flushed, all fine. They suspected a cracked head so we used some chemi weld stuff as a temporary measure. Then a while later it started doing it again. I pulled the radiator out and found it was totally sludged up. Threw it away and got a new one, did water pump etc too and the problem went away.
So while a cracked head is possible, exhaust other avenues first, esp pull the radiator out and give it a decent flush.