In the digital age we are used to micro electronic gadgets that never need adjustment. Even our automobiles can run for thousands of miles with almost no maintenance. But heavy equipment like marine diesels are different.

Most diesel engines need clean fuel, oil and air supplies, proper ignition and adequate cooling to provide long-lasting and reliable service. If you can take care of these items, your engine will almost always take care of you.

While engine and electrical maintenance are chores most boaters would rather not face, delaying them can drive up the cost of ownership in both time and money. Maintenance is also a matter of safety. In July of last year, Coast Guard officials in San Francisco estimated that engine failure caused one-third of the distress calls they receive.

The reality is that your power plant operates in a marine environment. Wiring is continually under attack by salt and moisture. Pumps are accosted by sand and marine organisms. Tanks are subject to condensation. Bolts can rattle loose.

In addition, the “new” boats that most of us buy are actually used, meaning they may have technology that is a decades old and was neglected by previous owners. Unlike most cars, marine engines need regular care. Without it, they will eventually succumb to the environment.

With that in mind, here are some ideas that will help prevent the most common problems from accosting one or both of your engines.

CLEAN FUEL

Many engine problems can be traced back to unclean fuel. You can guard against this by adding biocide and dewatering agents to your fuel tank before every filling, and by filtering the fuel through a fine mesh screen to remove unnecessary particles.CAPT. ALAN R. HUGENOT

In addition, half-empty tanks form condensation on the cold tank interiors, which then rusts the tanks and adds water to your fuel – two things that can mean trouble for a diesel engine. It is a good idea to keep your tanks full, which can help prevent condensation from forming.

Once a month, check the fuel filters to make sure they are clean, and drain off any water in the bulb. When you have rust flakes or algae, your filters fill up right away and need to be changed regularly, so carry two sets of replacements.

I once helped deliver a vessel from Lake Union in Seattle to Victoria that had spent the winter with empty fuel tanks. It had been a particularly cold winter, with several freezes, so the condensation had the chance to break out a good deal of rust from the tank sides. We topped off with diesel in Ballard, headed down through the Chittenden Locks to Puget Sound, then North to Victoria. That boat had dual bypass filters, meaning we could switch between them, and that was a good thing. Ultimately, we had to change the fuel filters four times during the 90-mile voyage.

CLEAN AIR

This is one of the least obvious and the most neglected items. Most engines will usually run with insufficient air, but the fuel economy goes way down and the horsepower suffers.

Every 90 days, check the engine air filters to see that they are clean, and disassemble them to clean or replace as necessary. Many boats have foam filters, which are very easy to clean. Just take it off and squeeze it like a sponge in some soapy water, rinse it, squeeze out all the water and put it back. If your engine has the automotive type paper filters, you should carry two spares and replace them regularly.

CLEAN OIL

Dirty lube oil in marine diesels contains the built up byproducts of combustion, which form acids that eat engines. The lube oil used in marine engines has additives that neutralize these acids, but the additives wear out. By changing the oil, you are protecting your engine against these acids.

If you have an older engine, you should change your lube oil after every 50 hours of engine use. Newer engines can go 100 hours. Comparing this to your car, at 60 miles an hour 50 hours would take you 3,000 miles, and 100 hours would take you 6,000 miles. Your boat needs its lube oil changed just as often as your car does. Always carry two sets of lube oil filters and enough oil to make one complete change. Each time you change oil, change the filters at the same time.CAPT. ALAN R. HUGENOT

Some boats do not have engine hour clocks, so use a rule of thumb to calculate the running hours. If you operate your boat two weekends a month for 6 hours each day, it adds 24 hours a month to your engine. The same schedule for four months of summer puts 100 hours on the engine, requiring only one oil change a year. For eight months of similar operation, change the oil twice a year, after four months and after eight months just before putting her away for the winter.

So change the oil in the fall, just before lay-up, while the engine is still warm from the last cruise. Change the oil and filter while the engine is hot, and then turn it over for five minutes to let the new oil come up in the engine, and shut her down for the winter. This technique keeps clean oil in the engine during the cold and prevents those acids from eating away. Waiting to change it in the spring gives the acids all winter long to feast.

If your boat is kept in water, another good idea is to go down once a month and light off the diesel, allowing it to run for 30 minutes in gear against the dock lines. This is a great exercise for a cold rainy Saturday in January -- it almost feels like you’ve been out cruising. But it also prevents the combustion byproducts from corroding the engine’s interior, because the lube oil, with its neutralizing additives, works up through the engine.

PROPER DIESEL IGNITION

It is surprising how many boats have trouble starting simply because there is too much resistance in the battery cables. Even though a diesel operates by spontaneous ignition, meaning pressure rather than a spark plug ignites the fuel, the diesel must be turning fast enough (usually about 600 RPM) to initiate the combustion just slightly before the cylinder reaches top dead center. Often, dirty battery terminals and salt build-up from the marine environment cause the slow cranking.

Oversized battery cables go a long way toward reducing the resistance, but so does regular maintenance.

Start by cleaning the battery terminals and the connections to the engine every 90 days. This means taking the connections apart and using a wire brush or sandpaper to sand the contact surfaces. The damp marine environment allows salt to creep in and corrode the terminals, forming an insulating barrier between loose contacts. When the contacts are thoroughly cleaned and tightly connected, protect them with a non-conducting coating or dielectric grease. This allows a metal-to-metal contact where the non-conducting grease is displaced, but the area around connector is protected from moisture and salts cannot get in. The grease must be non-conducting so it won’t form its own electrical pathway and short your systems. Ninety days later, wipe off the grease and clean the terminals again.

Also, be sure your batteries are topped off. Without water, the batteries can’t hold a charge – and the water continually evaporates as you charge the battery. Use distilled water and keep a funnel with a short hose handy to pour the water into the cells.

In addition, be careful not to overcharge your batteries. Many boaters leave their battery chargers plugged in all the time, hoping for a fully charged battery for their next run. With a modern digital charger, this may present no problem. But before the mid-1990’s, all battery chargers were built to continuously trickle charge at 3 amps, which can ruin a battery in six months. If you have an older boat, you may have an older charger as well, which will mean you will have to disconnect it after charging to avoid damage to the batteries.

If the battery juice seems too low to crank the engine, there are a few tricks to get started. Run jumper cables from the battery terminals to the engine and the starter, in parallel with the battery leads. This doubles the pathway and halves the resistance, causing more current to flow. Make sure you know where to connect to the positive lead on the starter, and connect the negative lead to the block as a ground. Adding the jumpers allows additional pathway for the current, which reduces the overall resistance proportionately.

I did this every time I started one of the engines on a commercial charter vessel, which had unusually long battery leads to one of the engines. The owners did not want to buy larger cables so the jumpers became standard.

When away from the dock and the engine won’t start, another trick is to stop and clean all the battery terminals and connections. Often salt has gotten in to create more resistance than your battery can handle. Once everything is clean, add a set of parallel jumpers and try starting again. More current will flow from your weak battery and the engine may just turn over.

ADEQUATE COOLING

Marine diesel engines are cooled using sea water (sometimes called raw water) and fouling from salt cake and marine organisms can be major problems.

The solution is to flush the system with fresh water as often as you can. Prior to starting the engine, back-flush the sea water intake by connecting the fresh water hose from the dock – this requires a fitting atop the sea strainer, or elsewhere in the cooling line – and forcing water to flow backwards out the seawater intake. This simple action will remove all the marine organisms trying to colonize. If successful, the little critters can prevent the flow of the necessary cooling water.

After shutting down, flushing the engine-cooling jacket with fresh water will help prevent salt cake and corrosion on the engine interior. Close the seacock and use that same hose connection to flush fresh water through the engine. It is not a good idea to run the engine using fresh water from the hose. Usually, a hose is small compared to the engine’s raw water intake, and may not provide enough cooling for the engine. Sometimes, when an engine is being tested ashore, a garden hose is used this way, but the engine should never be put under load or operated at higher than idle.

CAPT. ALAN R. HUGENOTOnce a year, replace the raw water pump impeller, which is the bladed rubber cylinder in the water pump that pulls sea water into the system. Install the spare you have on hand, and purchase a new spare. Sand particles get into the pump when a boat operates in shallow waters near shore. These particles wear out the impeller, which will then starve the engine of cooling water and cause it to overheat.

To change the impeller, close the seacock, locate the pump housing (check the manual or run back your cooling line) and remove the plate. Check which way the blades are turned, then pull the impeller from its housing. You may want to use a removal tool – Jabsco and other manufacturers make them – rather than a wrench, to avoid breaking off pieces of the impeller inside the housing. Slide the new impeller in place, with the blades facing properly. You might want to use a little dish soap to ease the insertion. Check the condition of the O-ring sealing the plate and replace it if necessary, then fit the plate back on and tighten it (remembering you want to remove it again next year. Run the engine and insure that cooling water is flowing out the exhaust as normal.

Changing the impeller can be difficult, because the housing is placed in a tight location on many boats, making it difficult to access. Working with tools and seeing what you are doing can be a challenge. But your engine cost thousands of dollars and it is worth the effort. You can purchase several items that can make this easier, such as an impeller removal tool and a Speedseal, which is a replacement for the housing cover that is self-seating and uses handcrews that can be manipulated without tools. (For a story on Speedseals, see link below).

Be sure to clean out the raw water strainer periodically, which can get clogged with debris brought in with the cooling water, and to exercise the seacock that controls the flow by opening and closing it. This insures that the valve works and is not frozen or clogged.

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.

Whether you are leaving the boat in the water or in dry dock, change the oil and filter, and run the engine to circulate the new oil; top off the fuel tanks and use the appropriate additives, and change the fuel filters; fill the batteries; and clean and dress the battery terminals. Charge the batteries fully, and then disconnect the terminals.

If you are leaving the boat in the water, test the bilge pumps to make sure they are operating; clean the engine’s seawater strainer and flush the cooling system intake with fresh water. If you live in a harsh winter climate, you’ll need to add antifreeze to the cooling line.

This is a job best done by two people. Close the seacock and open the strainer. Have several gallons of antifreeze open and ready. When your buddy starts the engine, you add the antifreeze to the strainer. It will be sucked up fast by the running engine. You want to pour quickly so that the engine does not starve for coolant and heat up (it helps to cut the tops off the antifreeze bottles). When you are down to your last gallon, have your friend cut the engine. Fill the rest of the strainer with antifreeze and replace the cap.

CAPT. ALAN R. HUGENOT

An alternative method is to add a hose attachment to your cooling line, run the hose to a five-gallon bucket filled with antifreeze, start the engine and shut it down when the bucket is empty. Either way, the idea is to fill the engine and the line with antifreeze, to protect it against the weather. Unless your engine has block heaters, you may also want to purchase marine-grade engine heaters such as those manufactured by Boatsafe Inc., and temporarily mount them in the engine compartment with wire ties. These are ambient heaters that trigger automatically in cold weather and give off only enough heat to keep the engine compartment temperature above freezing.

It is prudent to visit the boat weekly in winter to check for problems. At least once a month, run the engine under load until it reaches operating temperature of 1,000 degrees Fahrenheit (usually about 30 minutes), making sure to allow it to warm up and cool down properly. If you don’t start the engine to circulate the oil, combustion byproducts will rust the inside of the cylinder walls. Then, when you restart the engine in the spring, the rings will scrape that rust down into the crankcase and your oil pump will spread the grit throughout your engine. That will speed up the wear on all moving parts.

Capt. Alan Hugenot is a naval architect and marine surveyor based in San Francisco,whose writing has appeared regularly in Sea Magazine, Latitude 38, The Log newspaper, 48 Degrees North, Go Boating and many other boating publications on the Pacific coast. He serves as National Chairman of the Motor Yacht Technical Committee for the Society of Naval Architects and Marine Engineers.