Engine Pukes, What's Up?

[MJN]

The story so far.

My cooling system was not recovering coolant after cool down, so after the usual checks on radiator cap etc I deduced that it was probably the head gaskets starting to go. I had seen these symptoms before. So I changed the head gaskets and at the same time I switched to head studs instead of bolts to try to get a better clamping force on the heads.

OK, so I change the head gaskets and after the reassembly I have the car idling in the driveway. After about 10 minutes it starts to push coolant out of the overflow, then it starts to gush out the overflow. So I shut the motor off and it proceeds to dump probably 2 or 3 quarts of coolant in the driveway. It seemed like a lot more. So I let it cool off and refill the system. I have a ball valve in the back of the intake so I fill the system from the back to get all the air pockets out. I warm the motor up and it does it again. I also notice that I am getting coolant weeping (steaming) from around the head studs at the threads on the nuts.

So, I drain the coolant and one by one I pull the head studs, thoroughly clean the studs and the holes and reinstall with new sealer. After refilling the coolant I try again. Same thing, after about 10 minutes it starts pushing coolant. This time I raised the rpm’s a little and the coolant just exploded out the overflow in a foaming torrent. I had already noticed that the head studs still hadn’t sealed and were weeping.

I have just run a leak down test on the motor with the rocker arms pulled. I pressurized each cylinder at TDC and again at BDC thinking that I would be able to identify a cracked cylinder wall that way. The leak down checked out just fine. Between 2% and 4% on all cylinders top and bottom. This was on a stone cold engine, I had previously run it hot and the numbers were all less than 2%. I also left the cylinder pressurized for about 5 minutes and watched the coolant at the "T" filler for bubbles. I have a thermostat with a bleed hole so I figured that I would get bubbles if I have any leaks from the cylinder to the coolant passages either at the head gaskets or from a crack.

So what’s going on here? Are the weeping studs enough to do this? I wouldn’t have thought so. Do I have a cylinder wall crack that only opens up when the motors fully up to temperature? The cooling system seems to be OK otherwise. It will draw coolant back in from the overflow tank on cool down so there are no real leaks otherwise it would not pull a vacuum would it?

Any ideas???? I’m running out of things to try.