Originally Posted by WesK
A well respected diesel mechanic who used to work around my marina disagrees. He pointed out that one or more exhaust valves would be open to the atmosphere and moisture could get into one or more cylinders and cause rust. Running the engine periodically would alternate which cylinders are open to this possible condition. I suppose plugging the exhaust would take care of the problem. . . . . .
I didn't used to think that either, but learned the hard way when I was out of country for 6 months. Upon returning and starting port engine, exhaust valve was stuck closed and it bent a pushrod. Removed rocker shaft and tapped the end of the valve stem with a hammer a couple times and it popped open. Replaced the push rod and all was well.
Since that experience, I try to start the engines at least monthly or at a minimum roll them over with the starter for a few seconds every visit to the boat. If I go away that long again I will disconnect and plug the exhaust. If you do that, be sure and tag the throttles so no one tries to start the engines.