I just went through this with my Yanmar 3gmy that sat for 6 years. Here is what me and Ed Schenck did. First, my system had been dry for 6 years, so I disconnected the fresh water pump by taking off the belt. This will avoid burning up the impeller. Topped off the antifreeze, turned over a couple times and bled the fuel pump. Oil was fresh. Strapped on a fresh start battery, and after about 5 seconds of cranking, she fired up. After about 1 minute, she purred like a kitten. Remember, if you are NOT running fresh water through the heat exchanger, there are 2 areas to consider. Don't run it too long, there isn't that much coolant in the sealed system and it can get warm. 2. The exhaust does get hot. Again, if no fresh water, the exhaust is eventually going through your hull and fiberglass...it will get warm there too, so try to avoid running too long. After she smoothed out and only ran for a couple minutes, I did actually remove the thermostat to insure coolant throughout the entire block..I didn't want to run it too long with no fresh water to cool the system. Previous owner let mine set for 6 years and I can't tell you how pleased I was to hear it run perfectly. Mine has 421 hours on it and runs very strong. Bottom line, as all of the others have basically posted, it is a great engine... a little preparation and forethought.....and fire it up... Good luck.
