Outer Limits 4x4 Board

I've recently put a Jap import motor into my 3.0lt NJ Paj. At the time i replaced the water pump, thermostat, all hoses and had the radiator re-cored. I've notice a small split appear in the top tank where it seals against the core and took it back to the radiator repairer to be fixed. He reckons there is a pressure problem in the cooling system which has caused the radiator to "football" slightly causing the crack.

I have checked the thermostat (opens @ 87deg) and replaced the cap although i feel the cap was doing its job. So the only thing left could be exhaust gas getting into the cooling system. I have TK tested it (checked for CO in the system) under various conditions (hot, cold etc) and its checking out fine. There is no milk under the oil cap and doesn't seem to build up excessive pressure.

So i guess my question is, has anyone had a head crack where it's showed no signsor symptoms however when the heads have been removed there has been a crack? To me everything seems in order and i'm getting "d!cked" by the radiator fella. It would be good to hear your thoughts on this.

Cheers
Gabe

I haven't used the old TK for years as a gasket/head leak has to be so bad before it will change colour. Try a CO exhaust tester of a LPG gas tester, both work very well at picking up small leaks. If you are coming past Adelaide, sing out.
Steve

A mechanic 2 doors down has a gas analyser so i will check tomorrow. I just went for a drive, flogged the absolute shyte out of her for about 10 minutes. Came back and i could open the cap straight away and it had bugger all pressure. TK tested it again and its still blue. Will double check tomorrow then he can fix the split in the radiator.