Yacht Maintenance - Part 7: Boat Engines

If a diesel engine is serviced fairly regularly and treated reasonably during operation, it can run for many thousands of hours without problems: Let it warm up briefly before you get underway to let the oil circulate, and do not put it under full load immediately; do not switch it off again right after a few minutes and, on sailing yachts, no "motor sailing", because when the yacht heels under sail, it can affect effective lubrication in the engine, sometimes with fatal consequences. And what is really bad for the engine is when it is not used for long periods and has not been properly preserved before.

Changing the filters, especially the oil and diesel filters, and installing a new impeller are essential for a proper oil change. The impeller should also be renewed at the beginning of the season, which is always better than having to do it sometime in the summer.

Oil & oil filter change
There is not much to say about changing the oil: Use a hand pump (at operating temperature) to extract the oil from the dipstick tube or, if it is a newer engine, the dedicated tube somewhere on the side of the engine block. If the oil filter is changed regularly, it should not be too difficult to remove. Before you put the new filter on and screw it on loosely, at first, you should lubricate the rubber seal thinly with grease or diesel - then it will easily come off the following year. If the oil filter has not been changed for a longer period of time and has got stuck, sometimes unfortunately only brute force will help: Push a large, sturdy screwdriver through it and then use this lever to remove the filter. There is also a special tool with a tightening metal loop to remove stubborn filters, but this is usually only available to engine professionals.

Diesel Filter & Impeller
When changing the diesel filter, check the lines for possible leaks. In the worst case, air can enter and stop the engine. Changing the impeller usually is an easy task but with some engine models it gets rather fiddly. Usually the impeller housing is easily accessible at the bottom front of the engine, but on some makes (Yanmar for example) the water pump sits right in front of it. In such a case, it is usually easier and quicker to unscrew the pump to get to the impeller housing instead of fiddling around more or less blind and with bent fingers behind the pump.

V-Belts & Spark Plugs
Check the V-belt tension and tighten it if necessary. Incidentally, impellers and V-belts are spare and wear parts that always belong on board as a replacement. For gasoline or outboard engines, check and clean the spark plugs or replace them if necessary and, finally, you are ready for a great boating season as far as your engine is concerned.

However, the propulsion system continues outside the hull. Is the propeller firmly attached to the shaft? Does the shaft have any clearance? Is the zinc anode on the shaft still in good condition? As already said elsewhere in this series, it should be replaced if only 50 percent or less of the original is left. And, of course, it should not be painted over, either. Folding propellers should be easy going and re-greased. If your boat has a sail drive, the rubber sleeve on the hull must be replaced once every few years.

With these simple measures you should get through the season well with your engine. If, however, the engine is not running smoothly, if it suffers from starting problems or if it smokes heavily (whitish or dark) after starting, then it is time to consider a professional engine check by a specialist.

Text: Detlef Jens