What was the tip off that the engine was overheating?
It sounds like you know what you're doing and have thought about several
possible causes. I agree with you that it may be time for at least a new
set of plugs. You may have gotten it hot enough to deposit a little bit of
metal in the plugs that allow them to "pre-ignite" under load. Also, with
the high temp, you may have broken some of the deposits off the cyl head
that must be there after years of running. A good coating of deposits may
not cause a problem but with high temp, you may have cracked deposits with
glowing edges. In short, if the plugs and wires don't do it, I'd be ready
to pull the heads

"Chehalis Jeff" wrote in message
ups.com...
But he said all cylinder compression values were very close. If they
aren't leaking down, then how is that water getting in?

This is something that I have and are still considering as a possible
problem. I called a local OMC repair shop and that's what they
suggested - that when the engine gets warm enough and with enough
"suction" on the down stroke it could draw in just enough water (from a
'partially blown head gasket') to affect how it runs under load but not
enough to effect it otherwise. It's a possibility, however I would
think that there should be a way to tell if that's happening without
removing the head(s) and replacing the head gaskets. On the other hand,
that's not really a big, expensive or difficult job so maybe it's
worthwhile doing as a precaution.

JM