Okay so i need some help here. My neighbor has a 72 FJ55, with F engine which just went under a recent (less than 300 mile) rebuild by reputable shop. The problem is this, upon completion of rebuild the engine would start up and then shut right back down. This was solved and now we have this freeze plug issue. Issue being this: Engine ran well for about 1 hour...it then blew a freeze plug out (not due to freezing). What we believe is a pressure issue. It was then reassessed and the dowels in the head were missing causing the head gasket to be off, and upon ordering installing, pressure testing and new gasket, head was regrinded and reinstalled. Engine ran with no problems for about a week. It now has the reoccuring problem of a blown freeze plug....what we still believe is a pressure problem. New water pump, new thermostate and recored radiator. What can be causing this? Thanks in advance.