We have a Yanmar 3GM30-YEU in the LeComte. Raw water, heat exchanger. Put about 1200 hours on it in 11 years. Problems: fatigue failure of the 6" nipple between the exchanger and elbow (most are close-coupled; our engine was lower with respect to the muffler), one raw water pump (the YEU means that it was an engine meant for Europe and has a Swedish raw water pump), endless munching of alternator belts (the PO installed a 100amp Balmar). The engine itself required nothing but oil changes, never added any.