my explorer has a problem where it develops back pressure after it warms up and shoots antifreeze out of the overflow lid like a geyser. it only happens after it gets warm. my dealer replaced the water pump impellar nut which was a little loose and the bearing and seals but the problem is still there. could the head gasket seal ok until it warms up and contracts and then cause this problem? could this be caused by a bad head milling job? the problem never occured until i got the head milled.

 

head gasket
cracket head
cracked cooling jacket

tear it down and check it out