Maritme author Silver Donald Cameron completed a remarkable voyage around the entire island of Cape Breton in his engineless cutter Silversark. To put it in his own words: “engines in sailboats are an abomination – dirty, smelly, unreliable, expensive.” Though there is much to be said in support of Silver Donald’s point, most sailors today must stoically suffer the indignities that come with an iron jib while trying to understand it’s foibles.

Small marine diesels are simpler than their gasoline fuelled cousins. There are no spark plugs and no ignition system. In theory, given fuel and air, they pretty much have to run. Diesels rely on very high compression alone to ignite the fuel, so they are far heavier and more robust than gasoline engines. But beware. Neglect of basic maintenance routines will in time reduce that sweet singing diesel to a hundred kilos of rusty cast iron ballast.

Oil

  Most importantly of all, check your oil each time you start the engine. Lack of oil can bring you to a “Bang! Stop!” like nothing else.

  Change your oil before the winter. The products of diesel combustion containing acids and other corrosives are far more concentrated in diesel lube oil than in gasoline engines. Engine oil is easily removed through the dipstick hole using a small pump available at your local chandlery. Warm up the engine first to make things a lot easier.

 Use good quality oil. Modern engine oil contains 30% to 40% additives. These additives do a wide range of things including scrubbing, inhibiting corrosion and maintaining the thickness of the oil at high temperature. Although you can buy a liter of diesel oil for as little as $1.49, stick to quality brands. You get the additives you pay for.

  Don’t forget to change your oil filter when you change your oil. The old filter will contain the best part of a liter of dirty oil anyway.

  If your engine oil shows any sign of gray sludge on the dipstick or filler cap, water is somehow mixing with the oil. See “Siphon Breaks” below for the most likely cause.

  You should also change your saildrive or gearbox oil annually or as recommended in your manual. Use the recommended viscosity oil. Gearboxes and saildrives with oil that is too thick may not shift properly. Using oil that is too thin could lead to a serious “ Bang! Stop!”.

Fuel

  Diesels have a high-pressure fuel injector on each cylinder. Dirt, water and air stop fuel injectors dead.

  Fuel filters should be changed annually. The filter on the engine block is a fine filter (2 or 3 micron) capable of removing water, bacteria, sediment and dirt. Fill the new filter with fresh fuel and screw it on. Open the bleed screw on top of the filter housing and work the lever on the fuel pump a few times until the bubbles stop coming out the bleed hole. Close the bleed screw and you’re done.

  Never be tempted to use an oil filter in place of the fine filter on the engine block, even if it fits. Oil filters are much coarser and will not protect the engine properly.

  If you don’t already have one, consider installing a primary filter in front of your engine filter. Because the engine fine filter is enclosed in a can, you cannot see gross water build up. Also, the engine filter is so fine large solids can readily plug it. Primary filters are available with 20 to 30 micron cartridges. Accumulated water can be drained from the plastic bowl on the unit. Primary filters are a good investment.

  When you lay up your boat for the winter, fill the fuel tank to avoid condensation and add a biocide additive.

  If your engine starts running rough or changing RPM (“hunting”), you probably have air in the fuel system. Bleeding an engine involves opening each bleed point along the fuel path and pumping out any air bubbles with the manual fuel pump lever until you finally bleed at each injector. Bleeding can be frustrating. Your owner’s manual will show the location of each bleed point.

  Don’t run your engine with the fuel shut-off valve closed unless you require exhaustive practice bleeding your engine. I know this only too well.

Cooling Water

  Small marine diesels may be cooled by direct seawater or through a heat exchanger. In a typical wet exhaust system, seawater enters by way of a through hull fitting, circulates through the engine (or heat exchanger) and is discharged into the exhaust system at an “exhaust riser” behind the muffler.

The water pump in almost all cases turns a spider shaped neoprene impeller. If the flow of water out of the exhaust pipe drops off, you may have a worn impeller. In any case, the impeller should be removed annually at lay up, inspected and stored outside the pump. Impeller removal or replacement is dead simple. The water pump cover screws are removed, followed by the cover. The impeller is then pulled out. Slip jaw pliers work best.

  Make sure to replace the paper seal under the impeller cover. You can pump an amazing quantity of water into your boat through a damaged paper seal!

  Check your water hoses for signs of wear and replace as necessary – they’re fairly inexpensive. Use two “all 300” stainless steel screw clamps at each fitting. Cheap stainless steel screw clamps often only have a carbon steel screw that corrodes quickly.

  When you lay the boat up for winter, disconnect the water hose from the through hull and stick it in a container of plumbers antifreeze. Start the engine and draw the anti freeze through the system. Catch anything coming out the tailpipe in a bucket. Don’t even think about using expensive automobile antifreeze!  The ethylene glycol it contains is highly toxic in the environment.  

  If your engine is cooled by direct seawater, you will have to either drain the block or somehow get the antifreeze past your thermostat. This could be done by running the engine up to operating temperature first, or by removing the thermostat and replacing the housing. See your owners manual.

Siphon Breaks

When a sailboat heels, the exhaust outlet is often submerged and the motor dips under the waterline. Water can then back up the exhaust hose and siphon up the cooling water hoses into the cylinder head. At the very least, water in the engine results in a gray sludge in the oil that will lead to scored pistons and cylinder liners. At the worst, a cylinder full of water will snap a connecting rod like a chicken bone. (Water simply won’t compress!)

  These horrors can be avoided by looping the exhaust hose as high as it will go under the cockpit sole and installing an anti-siphon valve, also referred to as a vented loop, in your cockpit locker. See the accompanying illustration.

  As an alternative to the rather pricey vented loop, you can also install a “T” junction in the same location and lead a small hose overboard. Note, however, that this hose will squirt water whenever the engine is running.

  If you are installing a new section of exhaust hose, you should use the “certified” hose with the blue stripe. It will not catch fire if the exhaust goes dry.

Keeping Things Tight

  Your engine has four steel and rubber mounts that fasten it to the boat. You should check and tighten the bolts as they invariably work loose. Similarly, alternator belts should be kept snug and a spare belt carried aboard. It’s also a good idea to check, tighten and lubricate your shift linkages periodically.

Telltale Smoke

Happy diesels should have little or no exhaust smoke. When smoke is visible, its colour is the best indicator of what may be wrong inside. In general, blue smoke is very bad and usually warrants a solemn visit by a professional mechanic. The following chart can be used to navigate through the various possible causes of diesel smoke. The simplest things to check for are listed on the upper line.

Black Smoke		Blue Smoke	White Smoke
Lack of Air	Excess Fuel	Unburned Oil	Steam	Unburned Fuel
Dirty air filter Restricted exhaust Restricted air inlet, lack of engine ventilation	Engine overloaded Propeller too large Dirty fuel	Too much oil in engine	Engine overheating – check impeller, water inlet and thermostat	Air or Water in fuel Plugged fuel filter Engine not warmed up or running cold Low grade or dirty fuel
Incorrect valve clearance Faulty turbocharger (if fitted)	Faulty injector Improper injection timing Fuel delivery rate too high	Leaking rings, worn valve guides, worn seals, scored cylinder	Blown head gasket, cracked block, cracked head. Leaking heat exchanger (if fitted)	Faulty injector or injection timing Low compression