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.
