Reply to "Head problem??"

The most likely, even though it is UNLIKELY, is that the cap on the pressure tank isn't sealing at all.

You need to pressure test the entire system first. Then test the cap.

Buy or rent the Stant pressure testing kit. It's about $120 but it is worth it. It won't go to waste.

I don't have the temperature chart in front of me but I think that with no cap, the system will "boil over" at something like 215 degrees.

With the pressure cap, 16 pound, working and 50/50 anti-freeze, it won't boil over until 252.

That seems to be the most likely scenario.

Even if you have a new cap 1) sometimes they are bad out of the box 2) you may have a cap that is not compatible with the European filler neck on the pressure tank 3) even pressure test a new cap to be 100 % certain it is ok.

You do not want to be guessing at anything on a Pantera. For one thing, it is too difficult a car to work on and forget about having to fix it out on the road.