Has anyone considered converting a 2QM to a heat exchanger system from a 2GM? Does the thermostat stick less in antifreeze compared to freshwater or saltwater

I've never had a problem with the thermostat sticking on a raw-water-cooled 2QM here on the Chesapeake Bay ... nor have I ever heard of it as a difficulty for other J/30s here. I've found the engine to be remarkably reliable overall, with very few problems.

The Yanmar manual has a detailed section on the conversion to freshwater cooling.

I have a Yanmar manual you can borrow.

I thought about converting my engine to fresh-water cooling a few years ago. At the time, I talked to one of our local Yanmar gurus who strongly suggested that I NOT change over. His opinion was that the higher thermostat temperature setting would cause problems with both salt precipitatng out of solution as well as with the head gasket. His basic mantra was "if it works (and had been working for more than a dozen years), ... don't mess with it." He could have sold me several hundred dollars of parts to make the conversion, so I assumed he really believed that sticking with the raw-water cooling was the best idea.