I've got to protest your tearing right into a head gasket replacement JUST because the radiator tank keeps seperating.
This is not a "normal" symptom. You have a radiator cap (if you're the guy I'm thinking of) that apparently, by your posts, has not relieved ANY pressure. The tank seam is the only thing that goes. The cap is supposed to be the weak link in the system. I would thoroughly eliminate the rad as the source of your problem before undertaking a head gasket as the probable cause of this anomoly.
HERE'S A REALLY CHEAP TEST!!!!!
Go buy a lower pressure cap. Install it. If the seam still leaks ....ditch the rad and go get a metal one from one of the various radiator outlets that will give you an easy way for a whole lot less labor than you are about to undertake on the asumption that the head gasket is bad.
The exact same thing happened to me with my Caravan's rad. The upper tank started leaking at the upper seam. NO QUESTION ...I went and ordered a NEW rad. $129 delivered ( for a TJ they run between $198-229 depending on two core or three core).
End of problem.
What I would do if I had the tester (the shop radiator testing kit) is to warm the engine with the tester on and SEE what pressure the tank starts to leak. If it didn't do it at idle you could then PUMP up the cooling system pressure with the tester pump. If you exceed the cap relief pressure ........I'd say that the tank seam is at fault and it is an aboslute radiator temp problem. That is, that the rad can handle pressure fine UNTIL the rad temp goes beyond a certain limit ...then the faulty gasket/seam fails. That is, although your engine temp doesn't change much (typically) ..the rad temp varies quite a bit. At high speed/high ambient temp the heat rejection rate for some systems is just enough to keep the engine within operating specs. That is, the "reserve" capacity of the system is depleted and the rad temp will be much closer to the engine temp
You could also find this product at some local "full service" parts store ...or order it direct from the distributor ..but they charge you a $10 service fee on top of the product cost plus the S&H ( I think that they're a**hol*s for doing it). This will tell you beyond any doubt if you need to replace the head gasket.
THIS IS NOT TO SAY that you don't have a head gasket problem ...and I'm sure that somewhere in the world of blown head gaskets that there has been a situation that is identical to yours ...but I would think that hitting this weeks PA POWERBALL has better odds given the typical use that you described on other posts (just driving around and not just shutting down after a 200 mph run on the Salt Flats).
I just don't want to see you doing all that labor for something that may not exist.
Will someone else PLEASE pipe in here and support the thorough diagnosis avangel that I'm preaching? [img]images/graemlins/tongue.gif[/img]. Naturally I will accept the "well, you know I've seen this and that" and every other obscure nook and cranny (I once saw BIGFOOT = not the truck) type thing ...but what does MOST peoples common sense tell them?