Question: In PMY’s May issue, you stated that it’s not good to run a diesel engine for extended periods at idle. I plan on being away from my boat for two to three months and during that time, I plan on having someone periodically run my diesels dockside. Is this a good idea? And, if so, how often and how long should the engines be run and at what rpm? Should they be under load? Have any other suggestions?

— Russ Maclin Via e-mail

Professor Diesel: Normally, a diesel can remain unused for around two months without much attention. Since yours may be laid up longer, you should protect the fuel and cooling systems and internal and exterior parts from corrosion and rusting. (I assume that the boat is at a dock with shorepower to keep the batteries charged.) Rather than have someone idle the engines, I suggest you do the following: If you’re close to your oil and filter change interval, have it done so you’ll have fresh lube in the engine during layup. Whether you change oil or not, before you lay up the boat, take her out for an hour so you get the oil up to operating temperature. This will evaporate any moisture in it and help clean the inside of the engine. Top up the coolant. Check for coolant, fuel, and oil leaks. Fix any you find, then tighten all hose clamps. Wipe off any dirt, corrosion, and rust from the outside of the engine and transmission. Drain any water from your fuel-water separators, and prime the fuel system if necessary so it will be ready to start when you return. If your fuel tank has a drain, purge the water from it. Lubricate exposed sections of throttle and shift cables and their connections. Wrap and tape a plastic bag around the air cleaner/intake to prevent moisture from entering the engine or remove the air cleaner/intake and cover the air inlet with duct tape. Loosen drive belts to prevent stretching. Clean sea strainers and close seacocks. Clean and tighten battery-cable connections. If the boat will be laid up in a cold environment, winterize the seawater side of the engine with biodegradable antifreeze. Leave a list of everything you have done so that when you return, you will have a cheat sheet.

Professor Diesel is Larry Berlin, director of Mack Boring’s Training Services division.

This article originally appeared in the November 2011 issue of Power & Motoryacht magazine.