One thing I have been told is that the practice of plumbing a "T" style filler fitting in the top radiator hose is not a good idea as it is on the pressure side and coupled with a high volume pump could lead to overcoming the 7 psi pressure fill cap. I sure hope it is not the head gaskets. I built the motor about 10 years ago so I really cant count on memory but I am going to feel like a real dick if its the head gasket
