**snip**
the cooling
system just didn't seem to have the cooling capacity to handle heavy
loads (mountains) or high (80 degree plus) ambient temperatures**snip**

Last month when we were in Key West in our 85 Westy (with new head gaskets)
we experienced similar strange overheating issues. The van began to idle
intermittently and the temp gague shot up to the top and coolant spilled out
of the overflow tank.When we checked the actual temp ,in fact, the engine
was not overly hot. When we started the van to move it a few minutes later
the issue seemed to have resolved itself. This happened once more while in
the tropical climate, and hasn't happened since we returned here to the
freezer.

-Tracey