Always leave this valve closed when the engine is not in use. If the one of the engine's cooling system hoses breaks – they get weakened by alternately heating and cooling during engine operation – and if this valve is open, that leak can fill the boat with water.

PROPER OPERATION

Properly operating your engine is a wonderful preventative maintenance tool because it prevents carbon build-up. Taking the time to do this by the book will prevent a great deal of what passes for "normal" wear. At its most basic, proper operation means letting the engine warm up before taking off and letting it cool down before shutting if off.

New boat owners often wonder why their diesel engines don't have the same pick up as their gasoline car engines. They are used to jumping in their car, turning the starter and roaring out of the parking lot. Arriving at their vessel, they act the same. Leaving the dock five minutes after starting the engine, they leave the marina at slow speed but notice the diesel is sluggish when throttled up.

The diesel engine is fine. It just needs to warm up where a gasoline engine does not. Because diesels ignite fuel by compression, they generally require a temperature inside the cylinder of 750 degrees Fahrenheit to start and 1,000 degrees Fahrenheit to run efficiently. (For a story on temperature, see link below.)

We all want to get out on the water, so here's an easy way to slow down and give the engine the time it needs to run well. Start the diesel when you get to the boat, check to see that raw water is flowing from the exhaust and then let the engine idle while you load the stores and take care of other pre-departure chores. This will give your engine 15 to 20 minutes to reach operating temperature before you leave the slip. It is a good idea to place the engine under load while warming up by placing it in gear at idle and allowing the boat to push or pull against the dock lines. If this is not possible, then the engine should be run at full throttle for 10 minutes after leaving the moorage and getting out into the channel, in order to burn out the carbon.

Giving a diesel engine time to cool down is just as important. We typically shut a car engine off as soon as we park it, but that's not a good idea with a water-cooled marine engine. When coolant circulation stops on a car engine, the coolant will heat up temporarily near the cylinders, so a sudden shutdown has no long-term consequences. In a boat engine, though, this temporary increase in local temperature causes the sea water in the engine water jacket to boil off, and salt cake to form. Over time, this can build up and prevent efficient cooling, causing the engine to overheat easily.

The solution is to always let the engine idle for five minutes with no load before shutting down, allowing it to cool properly. This should be done when you return to the dock after a cruise and also after setting anchor. Sail boaters especially need to resist the temptation to shut down that "noisy" engine after they set sail, and instead force themselves to let it idle for five minutes.

It is important to limit the cooling down idle time to five minutes. This is sufficient time for it to cool down, but will not allow carbon to build up on the interior, which can happen to diesels at idle. Warming up under load prevents this carbon build-up.

WINTERIZATION

What you do during the months the boat is not in use can be as important as how you maintain her during boating season. Winterizing a boat's many systems could be the subject of its own story, so we'll deal only with diesel engines here.