Diesel engine care, battery choices, evaluating old sails

Q: I keep hearing that diesel engines “like” to be worked hard. I also understand that it can be a problem only using an auxiliary for brief periods, like just going in and out of a marina, as opposed to prolonged periods. Why is this? How much should a diesel be run to keep it in good shape, and what can a daysailer like me do to make sure I get in the right amount of run time? — Scott Henderson, Houston, TX

NIGEL CALDER REPLIES

When a diesel engine is first warmed up, it is considerably less efficient than when it has fully warmed, especially if run at low power levels, such as when maneuvering in harbor, battery-charging at anchor or running a generator with light loads. Less efficiency plus cool engine surfaces result in poor fuel combustion, which trans- lates into carbon. This carbon then plugs piston rings in their grooves, lowering compression ratios, and also plates out on valves and throughout the exhaust system. Both things are really bad for the engine.

Any time you crank a diesel, you should aim to put a respectable load on it as soon as possible and to maintain that load until the engine is fully warmed up. Unfortunately, because it takes very little energy to move our boats at slow speeds, we can’t create much of a load until clear of a harbor. The keys are to avoid unnecessary dockside idling, get clear of the harbor as soon as possible and then, at least once every few times in and out of your slip, run the engine at around two thirds throttle or higher for at least 10 or 15 minutes. This will help to minimize any carbon formation.

If in doubt about your operating practices, pull the exhaust hose off the back of the engine and look in the exhaust elbow. If there is a carbon crust baked on in there you are not running the engine nearly hard enough.

Simply motoring in and out of a slip is not enough use to keep your diesel engine working well