Potential issues for underused Yanmar

[svporfin]

Hey all. Looking at 10 yr old sailboat with only 300 hours on 100 hp Yanmar. What should I be prepared for in terms of maintenance and longevity given that this engine has effectively not been used? Would you change any components / parts day one? Thanks for any advice!

[Pitchondesign]

I had a generator that had not been used in three years. It was hard starting. I had a compression test done and found that 2 of the 4 cylinders were low on compression. We took the head off and found that the valves and seats were corroded. Apparently when a engine sits, some of the exhaust valves remain open, which is normal. In a wet exhaust engine, the muffler will have some sea water sitting. Because it is a closed system, with the water vapor from the muffler in direct contact with the open exhaust valves and pistons, corrosion is a certainty. When a engine is run regularly, the oil coats these surfaces, so no corrosion. When an engine sits for a prolonged period, the oil coating diminishes, and corrosion starts. A compression check will reveal if an engine has this issue. Proper storage can prevent this problem.

[Lepke]

Most diesel engines fair well sitting. Stuck pistons rarely happen compared to gas engines. It's always better if an engine is started and warmed often, but if it starts easy and doesn't smoke and only has a few hours, it's probably in good shape. I've rebulit many engines and started many diesels that sat for years and some that sat decades. Mostly heavy duty diesels. Only a couple had problems that required opening the engine.
I have automatic drain valves on my water mufflers. When the engine shuts down, the exhaust pressure no longer holds the valve closed and the water drains. It also makes starting easier - no back pressure.