[speeder]

OK, finally updating this. The problem is a blockage somewhere in the heater plumbing. This car has a very convoluted coolant flow design, (you should see the diagram!). Even with the heat turned off, the coolant has to pass through most of the plumbing before it gets from the left head over to the right. There is something rusted partly shut inside the car, near the heater core. At the moment, the entire heat system is bypassed and it is not overheating or running hot.

Getting to the heater cores is a 24 hour book job at the dealer. It's a nightmare. I am going to try to clear it or flush the hairball out from the firewall, but it probably won't work.

It was neccessary to remove the heads to eliminate any blockage inside of engine. There was some crap in cooling passages but not enough to cause the problem.