Yanmar's that run hotter every year.

[Pgisailor]

I wanted to share the fix to my five year battle. If your engine over heats at medium to high RPM try draining your year old antifreeze and flush with fresh water. Drain and flush again to get all the antifreeze out of the system, running your engine each time you flush, enough to get the engine thermostat open. Then use Zerex Radiator Super Cleaner flush, follow directions. Be sure and run your engine for at least four to six hours with the Zerex Flush. Zerex is green when you pour it in. After running your engine for four to six hours it should come out light brown or the color of coffee if your heat exchanger build up was like mine in a seven year old boat. Drain your engine and flush with fresh water. Drain it a second time and flush again. Now fill with NAPA heavy duty antifreeze mixed 50/50. Do not put antifreeze concentrate in the engine followed by water and expect the engine to mix it up. This method "Scales" the heat exchanger tubes. With your problem fixed, never use Dex Cool again. Disclaimer: I do not work for NAPA, I don't know anyone at NAPA, I do not own NAPA stock. I fought my 54 hp Yanmar over heating for five years. This fixed my problem completely. You can not know how great I now feel about my 41 Hunter.