ok this is something that has been bugging me for awhile. well i will say 3 years ago i burned a valve on my gsr head. ok i replaces the valve an had the machine shop pressure test the head an surface it. i installed itr pistons. i put it back togather an i noticed that the rad would still hold pressure after the car had sat for awhile. it could sit for 2 days an i take the cap off it release the pressure. drove it like that for awhile. ok pulled the head off some more work put head studs in an i still hadthe same thing going on. ok this last time i had screwed myself an blowed the headgasket. i had another head so i had it worked an what not, swaped them out "still head studs" an the prob is gone. i have been racking my brain on what could have gone wrong with that head to cause that to happen. i just want to see what any body else can come up with.