N.B.: I have no
experience with this engine, this type of "dual loop" coolant system, or marine engines, in general.
Anyway after several hours of diagnosis and work, it turns out the coolant (some sort of biodegradeable version) used has not been changed in some time, and according to the Captain who agreed to watch over the mechanics for me, it had sludged up the thermostat pretty good. The yard replaced the theromstat and removed and flushed the heat exchanger and now says the engine was showing around 170 degrees running hard.
If what I think of as the "inner loop" of this coolant system is alike a regular automotive engine coolant system, that sounds like it'll probably
My concern is could the engine itself be sludged up as well,
I would imagine this is possible.
and what if anything to do about it?
Only thing you could do more, I would think, is an acid flush of the water jackets in the engine. (Which I'd do in your place eventually, anyway, given what you've told us.)
Please share your thoughts, advice and commiserations.
I get the impression the mechanic's "worst he's ever seen" evaluation was before
the repair? He seems to think it's okay now?
If you're not comfortable having the captain give it another go, on that, ask the yard as to the advisability of an acid flush for the engine, I guess. That's about all that's left, to the best of my limited knowledge.