RE: Unexplained overheating problem
I went through several years of similar overheating problems with my '85
Westy 1.9l. The biggest clue, but the most subtle, was that the cooling
system just didn't seem to have the cooling capacity to handle heavy
loads (mountains) or high (80 degree plus) ambient temperatures.  To
shorten the story, THE PROBLEM WAS THE RADIATOR. And it is apparently
not possible to check the flow of the radiator.  The bottom line for me
was that if I had followed my gut feel to have the radiator replaced
regardless of all the experts opinions I would have saved and engine.