What’s a diesel and how do I take care of it?

If you compare a gas engine to a diesel, in an abstract way they are very similar. In a gas engine, a fuel air mixture is drawn in through the intake from injectors or by vacuum through the carburetor as the intake valve opens and the piston is drawn downward; nearing the bottom of the piston travel, the piston starts upward and the intake valve closes and the air/fuel mixture becomes compressed, nearing the top of the compression stroke. At the same time the distributor selects the proper cylinder and sends a electrical impulse to the coil which in turn raises 12 volts DC current up 20,000 volts and in some cases higher, this current is sent back to the distributor and in turn to the sparkplug, which ignites the air/fuel mixture as a controlled explosion. Gas engines are low compressions engines usually 7-9 to 1 compression ration.

Diesel engines operate on a much high compression ratio ranging from 15:1 and upward, many modern engines run at 21:1 ratio. Similar to gas engines, diesel fuel is drawn from the fuel tank on smaller diesel at around 6 PSI by the lift pump is then delivered to the injection pump which acts similar to the gas engine electrical distributor, only in this case distributes fuel to the designated cylinder at a highly compressed state of 1,200 PSI or higher. The injection pump delivers highly compressed fuel to the fuel injector; the injector when reaching the desired pressure pops open and delivers finely atomized fuel to the cylinder. Unlike the gas engine which uses a spark plug to ignite the fuel, diesel is injected into the cylinder much earlier before the piston reaches the top of its compression stroke, as the compression levels rise the fuel slowly starts to burn, more of a controlled burn rather than the controlled explosion experienced by the gas engine.

Modern electronic diesels carry the injection and control process to a refined art, in some cases injecting fuel up to 8 times during the compression stroke and can vary the number of injections and timing of the injections to compensate for engine loads. These new engines are much quieter, fuel efficient, have lower emissions and are smoother running diesel.

Diesel Care

Clean fuel: One thing diesel don’t tolerate very well is dirty fuel. Clean fuel starts with the deck mounted fuel fill where you fill up your tank, check the o-ring in the cap and make sure it is clean and in good condition, if not replace it; also check the fuel filler neck where the cap screws in and make sure the threads and the area where the o-ring seats is clean, a little Vaseline on the o-ring and threads will help it seal properly and make it easy to remove in the future. This should reduce or eliminate rain and boat wash down water from entering the fuel tank.

Always use clean fuel from a reliable source, marina fuel docks known for selling a lot of fuel are probably your best sources as the fuel in the storage tank has not been sitting for prolonged periods, and is refreshed often.

Change all your fuel filters, the primary fuel filter between the fuel tank and the engine and the secondary, engine-mounted filter. Conservative estimates on engine run time per filter changes are 200 hours or one year which ever comes first; of course providing you have relatively clean fuel to begin with. If you have a see through filter bowl on the bottom of your primary fuel filter, check it for water and/or contaminates before operating your engine, if found, drain the water and contaminates, bleed the air out of your fuel system and run your engine at the dock for 20 minutes before taking it out on the water to make sure all of the air is removed from the fuel system; if the engine stalls or dies, re-bleed the fuel system to remove remaining air and test run again. See your engine owner’s manual for fuel system bleeding instructions or make an appointment with your mechanic so he can walk you through the process.

Keep your fuel tank full, partially full tanks allow an opportunity for condensation to form (water); this moisture enters with air through the fuel tank vent. This water collects on the sides of the tank and flows to the bottom of the tank where your engine gets it fuel first.

Fuel additives: We prefer to use an enzyme product aimed at prevention of the formation of algae, fungus and bacteria, aids in performance enhancement, lower emissions and lubrication vs. biocides which are aimed at killing the aforementioned after the problem occurs. If you have clean fuel we use a product called Soltron. If their is a problem with growth we prefer to use a biocide such as Valvetec product called Biobor or Bio-Guard; Biobor is aimed solely at killing the growth, while Bio-Guard has lower level of biocides it is oriented towards prevention, with additives promoting performance, lubrication and cleaning. While all these products serve a purpose, we prefer to sidestep the use of biocides in favor of less personal and environmentally non toxic solutions such as enzymes where possible.
 
If you have contaminated fuel, we recommend that you double dose you fuel with biocide, let it sit for a week, thus allowing it to kill the bacteria in the tank. When you add the biocide call your local fuel polisher and schedule an appointment to have your fuel tank cleaned one to two weeks later.
 
Fuel polishing is a misnomer. Done properly, the person will test for water and pump out the water from the bottom of the tank first, and then they will pump the fuel out of your tank through a series of filters removing the contaminates and return it to your tank. Through this process the fuel is moved through the tank breaking up the dead growth allowing it to be filtered before returning it to the tank. After the fuel has been cleaned change all your fuel filters and plan on replacing them in about 15 hours of operation as there will always be some residual debris in the tank or fuel lines which will collect in the filters.

The most common failure to start or run following a fuel polishing is failure to repeat the fuel filter replacement process, which becomes plugged by residual dead bacteria. It’s important to remember fuel tanks have dividers called baffles; these baffles control the bulk movement of the fuel, slowing its side-to-side movement. When possible we recommend having access ports installed in the top of the tank between these baffles to allow access when fuel polishing and when access is needed to clean your tank manually.
 
Never polish or clean old fuel, diesel starts to loose it peak performance after one year and degrades sharply in following years; Old fuel will build up varnish in the expensive injection pump and injectors causing lower performance and eventual failure of these components. If you have a long-term storage problem with to much fuel, to many tanks, consider empting the tanks not used and run on one tank of fresh fuel. If you have one large tank consider reducing the size of the fuel tank replacing it with a smaller tank. If you must run on old fuel, try adding new fuel with the bulk of the fuel being new fuel. If you have fuel two or more years old we recommend pumping it out, cleaning your tank manually and taking the old fuel to your county waste disposal site.

Annual maintenance: As a minimum we recommend you have your oil and filter and transmission oil changed, replace your seawater pump impeller, heat exchanger zinc and fuel filter. You may need to change your oil and filter more often if you accumulate a significant number of operating hours prior to your scheduled annual maintenance, please consult your owner’s manual for hourly change recommendations.

Pre-start checks:

Check all fluid levels: Check your engine and transmission oil levels, check the condition of the oil, oil from diesel is generally black from carbon this is normal, check for viscosity, thickening from heavy carbon deposits, more so with prolonged idle times, if excessively thick or gritty change the oil. Engine oil and filters should be changed every 150 hours of operation or annually which ever comes first, consult your manufacturers manual to verify their recommendations. Also smell the oil to check for unusual smells, like fuel, or a burned smell; if you smell fuel call your mechanic.

Check your anti-freeze level if you engine has a heat exchanger and top off your engine over flow reservoir (plastic tank) up with a 50/50% mix of anti-freeze and water. With ethylene glycol (green stuff) should be changed every two years; with the long life such as DEX-COOL approved usually the red or pink anti-freeze it should be changed every 5 years.
 
Check your V-belt tension, looks like a fan belt, but of course boats don’t have fans, should be 3/8” to ½” deflection in the belt, not hard but firm tension on the longest run between pulleys; if there is any question of proper tension ask your mechanic to show you the proper method of checking belt tension.

General check: Check all your hoses and pipes for any loose, cracked or leaking and make any necessary repairs before operating your engine.

Engine start checks:

Verify that the valve called the seacock for your engine cooling water is turned on and check the seawater strainer is clean and free of debris. If you shut off your seacock it is recommended that your store your ignition key on your seacock handle to prevent you from starting your engine before opening the seacock.

Some engines may require it and some may not, first turn on your ignition and leave your throttle at the idle position, some may require a little more throttle to start. If your engine has glow plugs, usually depressing the glow plug button for 15 seconds, some a little more, then depress the start button or turn the key as required; if the engine does not immediately start, use the glow plug again, do not continue to crank the engine. If not equipped with a glow plug system, simply turning the ignition switch beyond the on position like a car will start it.

Warning: if your engine fails to start, do not continue to crank the engine, as the seawater pump will continue to pump water filling up your muffler and backing up water into your engine. Your engine cylinder will fill with water and your engine will attempt to compress water (Hydro-lock); this can cause permanent damage to your engine.

On most small 1-4 cylinder diesel idle speed on a cold engine is very rough, we recommend advancing the idle to 1,000 RPM as soon as the low oil pressure light or alarm goes out, this will smooth out the engine till warm, approximately 5 minutes. It is not necessary for your engine to reach full operating temperature before getting underway.

After your start your engine, go back to the transom of your boat and check for cooling water flow from your exhaust, if it comes out immediately wait and watch the water flow for at least 30 seconds to see if it continues; it very common for people to take a quick glance, see water and go about their business, to find it was only the residual water from the muffler and the seacock was left closed, this will almost certainly result in the exhaust system running dry, burn up the seawater pump impeller, the exhaust system and over heat your engine.

Next go back to the engine compartment and looks for leaks, take your time, look for any possible water, oil and fuel leaks, specifically look at your seawater pump to see if it is leaking, if so stop your engine and make repairs or call your mechanic.

If everything looks ok then take your boat out, gradually allowing the engine to come up to operating temperature before advancing the throttle above half throttle, no sense dumping a lot of fuel into a cold engine.

On the water operation:

Vary your throttle settings, not like a Yo-Yo, but generally up or down a few hundred RPM from time to time on a long run. Despite what we have heard, prolonged idling is not good for any engine, usually results in higher carbon build up in the oil, most diesels will accept prolonged idle periods, but generally like to work hard. The general rule of thumb for best fuel economy and best speed is around 70% of max RPM. We usually recommend 4 minute max RPM runs in gear away from the dock at least once a month to reduce carbon build up in the head and exhaust system, don’t be alarmed the engines are factory governed to allow this and it’s good for your diesel.

When your return to the dock, idle the engine for 5 minutes to allow it to cool, especially important for turbocharged engines to cool the turbo to save the bearings. Once you have cooled the engine for 5 minutes, in neutral, raise the RPM for 4 seconds in neutral, burns off the carbon accumulated while idling, then back to idle allowing the engine to smooth out then stop your engine by pulling the engine stop cable or turning off the key if your engine does not have a stop cable and is designed to be stopped in this manner; Never turn off your ignition switch before pulling the stop cable as this turns off the electrical system and may fry the diodes in your alternator, if there is any question check your engines owners manual.

Cooling systems:

Essentially there are 3 types of cooling systems most commonly used.

1  Seawater cooling: Seawater is drawn from outside the hull via a valve called a seacock, the water flows through a seawater strainer, used to strain large particles of foreign matter, grass, clams, muscles, small fish etc. From the strainer the water travels to the seawater pump to the engine and exits the engine to enter what is called an exhaust mixing elbow, usually a u-shaped cast assembly which allows water to enter and cool the rubber exhaust hose as the hose leads to the muffler; from the muffler the exhaust hose travels to the transom and is expelled back into the sea.

2 Freshwater cooling: Like the seawater cooled system, seawater leaves the seawater pump, but does not go through the engine block, it goes into a heat exchanger and possibility through one or two oil coolers, used to cool engine oil and/or transmission fluid. The heat exchanger is usually a large round tube 2” in diameter or larger, this tube has one large round plate sealing off each end of the tube an inch or two back from the end, these plates are perforated and small tubes are silver soldiered to these plates. Seawater from the pump is pumped through these small tubes on it way to the exhaust-mixing elbow. Like your car and its circulation pump behind the fan, this pump, pumps anti-freeze through the engine block and head, then through the radiator; in your boat the radiator is replaced with the heat exchanger and anti-freeze is pumped into the side of the exchanger between the small tubes, as anti-freeze circulates through the exchanger, the cool seawater running through the small tubes allows the heat transfer (conducted) through the tube walls from the anti-freeze to the seawater before it leaves the exchanger and is expelled through the exhaust mixing elbow. The flow of seawater is similar to air passing through your car radiator. Your heat exchanger has a pencil zinc, a zinc screwed into a pipe plug which is in turn screwed into the seawater side, this zinc is essential to minimizing electrolysis and subsequent loss of parent metal of the exchanger, check this quarterly to monitor the reduction is size, when it reaches 1/3 it original size replace it. Use liquid pipe sealant available at your local hardware store to seal the threads of the zinc, prevent leakage and subsequent corrosion damage to the treads in the exchanger; not to worry, we have proven liquid sealant does not affect continuity or connectivity of the zinc to the exchanger, it safe, and please remember to not over tighten the zinc plug as this will damage the exchanger, you want the zinc just tight enough so it doesn’t leak or fall out.

3 Keel cooling: Although given the name, may not use the keel to cool the engine. In this case the seawater cooling system is totally omitted. In place of the round tube type heat exchanger, anti-freeze is pumped outside the hull through a manifold to a series of tubes exposed directly to seawater and is pumped back into the hull after passing through these tubes and back into the engine. Like the heat exchanger the heat from the engine is conducted through the tubing directly to surrounding seawater outside the hull. The exhaust is insulated and directed upward through the deck in a chimney called a dry stack to the atmosphere, similar to your cars exhaust. Mostly used in commercial craft and large powerboats.

Heat exchangers, myths and mistakes: The old school method of cleaning the heat exchanger seawater cooling tubes was to remove the end-caps and run a wooden rod through the tubes to clear obstructions and build up. Unknown at the time this procedure was invented, is that harden minerals imbed into the wooden rod like gluing sand to the wood (sand paper), these hard particles cut groves or scratches into the inner surface of the tubes as the rod is passed through the tubes, increasing the rate of erosion and premature exchanger failure. The proper procedure is to remove the exchanger and take it to a radiator shop that specializes in marine exchanger, they will soak the exchanger over night to soften the mineral deposits then scrub them out with a hard to find miniature nylon brush. They will also clean out the anti-freeze side, between and around the tubes; cleaning the seawater side, inside the tubes, is only part of the process. After cleaning they will pressure check the exchanger to ensure it will hold pressure without leaking. Big myth, cleaning the exchanger will renew it indefinitely. Depending on its age condition, construction may last up to 5,000 hours of operation, a lot depends on if the zincs were changed while 1/3 of the zinc material remained, prolonged periods of operation without a working zinc, years in use, weather it was a premium quality or bargain basement constructed exchanger, made of long lasting copper-nickel or lower grade copper (normal). We have seen small pinholes or fissures in a cleaned exchanger, that was pressure checked good, open up once the engine came up to operating temperature. It is important to remember, time and corrosion takes it toll, cleaning is not renewing, if there is any doubt replace it, when an exchanger fails it pumps all the anti-freeze from the block out the exhaust with the seawater and your engine will overheat.
 
Oil coolers: similar to heat exchangers oil coolers pump engine oil or transmission fluid around and between the tubes in place of anti-freeze. A more critical eye should be focused on these coolers as failure will lead to seawater entering the engine and transmission oil with subsequent total loss of the engine or transmission, about 2,500 hours of operation is the safe limit, bearing in mind most oil cooler do not have protective zincs especially in small boats, if in doubt replace it, its better to be safe than sorry and it’s a lot cheaper to replace a $95 oil cooler on a small diesel than it is to pay $16,000 for a new engine.

Best advise I can give, no matter what you do, sometime things just break, so buy the best boat towing insurance policy your can afford for your given area of operation; there is nothing worse than fretting about a broken engine, while at the same time worrying about an outrageously expensive towing bill. Towing generally runs $120 per hour from the time the towboat leaves their dock to the time they return and they deserve every penny. A towboat skipper once described his job as vast expanses of time spent in total boredom waiting for the next call, interrupted by moments of shear terror, high winds, rough seas, lee shore and dragging anchors; seldom is it calm seas, sunny skys and flat seas. We get free towing up to 50 miles out to sea for $85 per year, cheap insurance. And by all means call your mechanic and pay for a one on one training session to learn how your engine works and what to do in the event things go south.

Best tip of the day: Take a friend sailing/power boating and have a great day on the bay.

Cheers,

Marty Chin

Phone: (510) 435-8870
2021 Alaska Packer Place,
Box 11
Alameda, CA. 94501