hmmm unfortunate but i had close to the same issue with my rebuild once it was started the first time but but it would overflow the coolant after a say 10mile drive once i parked it a couple min later. it was doing everything of a coolant seal failure or pinch except lots of white smoke in the exhaust. so i decided to do the one last test and test the block with a pinnapple racing style coolant seal presure checker. the one i made is in my build thread but you can also see it on pinnapples site.
http://www.pineappleracing.com/index...ROD&ProdID=142
well turned out my drain plug was just loose enough to allow air into the system on shutdown then once restarted the coolant would have air in the system making it overflow.
could try that before you pull or split the keg.
z