[C320-list] Dropping water temperature

[Bruce Stumpp]

We motored home today at 2,800 RPM's for about 3 hours.  The temperature
gauge read 180 degrees for about 2.5 hours but the next time I looked it had
dropped to about 140-150 degrees.   I shut down the engine, was able to
catch a small breeze and used the motor just to get into the slip.   Engine
is a Yanmar.   I'm thinking the thermostat was stuck open.  Does anyone have
any other thoughts, suggestions or experience with this situation?

Bruce Stumpp
Adventure, #647 
Frog Mortar Creek, MD