I've wondered about the thermostat, too....
In looking through a 2GM manual, I noticed that there's an engine block coolant drain. It's a valve on the stbd side of the engine with a plastic tube leading down from it. What I do after the boat is on the hard is first drain the water out of the block, then pump 3 gallons of antifreeze through the engine. As I figure, even if the thermostat doesn't open, I should still be safe.
Now I don't know if the 2QM has such a drain.
