"Ahh... there is nothing like the fresh smell of diesel fuel in the morning...."


  Specific Diesel mechanical issues are highlighted here. General electrical, drive train, and accessories are,  covered in content, by the rest of this web site. Keep in mind that most of the references on those other pages are written, primarily, for gas installation, but a lot of specification codes, are not written specific to gas or diesel.

  There are a lot of things to consider when buying and/or operating  a diesel powered boat. Often overlooked as a power source, when comparing initial cost to use (compared to gas power plants) by recreational boaters, the commercial power plant of choice is almost always diesel. Recreational weekend warriors who have diesels usually find that the engine will  rust to death long before they wear it out. So they are not for everyone. 

  With the new offerings of both diesel inboard and diesel sterndrive by several of the top marine engine suppliers, we recommend a closer look at these choices when it's time to re-power your boat or yacht.


A bit about diesel fuel

Large fuel droplets and high "asphalting" concentrations of diesel fuel require more time, more energy and higher temperatures to combust than is available in diesel engines during the combustion cycle. Age of the fuel as well as any device in the fuel system exposing the fuel to stress (heat and pressure) such as injector pumps, fuel heaters, or fuel centrifuges will increase the formation of asphaltenes. If you have diesel fuel that has turned dark, or almost black, in comparison to clear, bright fuel, then it is time to call your local fuel polishing company. This degraded, dark fuel negatively impacts combustion and performance of the engine and can prevent the engine from starting in the first place.

Diesel Dos and Don'ts

  • Don't start a diesel engine without checking fluid levels.

  • Corrosion is a big danger to a diesel engine. Try to operate a marine diesel at least every 30 days. Allow the engine to warm up completely, then run throttle up to about 1500 RPM for about 5 minutes before shutting it down.

  • Properly condition marine diesel engines that aren't going to be used for periods of greater than 30 days. Long periods of disuse results in serious internal engine rusting of cylinder walls and valves.

  • Do not start a diesel engine with the throttle advanced.   Do not load or race a diesel engine until it is up to normal operating temperature. Due to internal loads and engine tolerances, this is very damaging.

  • A diesel engine is designed to operate at mid to full throttle effectively. So, try to avoid prolonged idling if possible. When trolling or idling for long periods, always run the engine at cruise speed or higher on the way home for at least 30 minutes to clean out carbon deposits.

  • Add a diesel fuel additive regularly to prevent the fuel system from becoming contaminated. Check and service fuel systems immediately if excessive exhaust emissions occur. 
    [Contaminant build up resulting from excessive microbial growth and bio-degradation of diesel fuel can cause fuel filter plugging. Micro-organisms, bacteria and enzyme activity, fungus, yeast and mold cause diesel fuel degradation and the formation of waste products. The process is similar to milk turning sour. Of all the microbial debris and waste products in the diesel fuel tank only about .01% are microbes. Even though microbes may cause and accelerate the process of fuel degradation, as a general situation, the waste products clogging your filter are not the microbes but fuel components which have formed solids.]

  • Do not operate a diesel powered boat at high speed when excessive vibration occurs. The internal parts of a marine diesel engine already has enough vibration to deal with when they're running properly. Serious vibrations caused by external issues and/or an issue with the engine itself can quickly destroy a diesel engine. 


  Ether and Diesels...

"Never use ether  or "starting fluid" to start a diesel engine."

  If it won't start like it normally does, then look for the cause. If it has just been getting harder and harder to start, over a period of time... get a compression test.

  We received an email question concerning the use of ether to start a sluggish diesel. It is very dangerous to implement this procedure. Serious damage can and will occur, if implemented incorrectly. However, in an emergency there are other concerns that might tempt you to try desperate acts to try to get your diesel started and out of danger.

Notice: Electronically controlled diesel engines have special sensors that can/will be damaged and/or thrown out of calibration if subjected to unusual starting procedures, other than those listed in the owners manual.

  So, having said that, we'll tempt fate and give you the secret that could keep you off the rocks some day. 

First, if your engine has a manual fuel primer lever, pump the lever until it gets firm. Make sure that the transmission is in neutral and that the engine "cranks freely" and is not hydro-locked. (see salvaging a drowned motor

Then, remove any panel that would be necessary to ventilate the engine room. Turn on any blowers and/or ventilation equipment that would aid in keeping the engine room well ventilated.

   If the engine has a cylinder compression relief valve, (usually a lever located next to the valve cover) open the valve, and have someone crank the engine. When the engine achieves maximum cranking speed, rapidly close the pressure relief valve and often this will start the engine. A low battery and/or cold conditions may require several attempts at this procedure.

Warning: Continued cranking of an engine attached to a  water lift muffler, can cause the muffler to fill with water and back-flow into the engine. (causing hydro-lock) Always shut off the water supply to an engine that won't start and open the valve as soon as it does start.

  Engines that are not equipped with a cylinder compression pressure relief valve can be a little trickier. 

First, follow the safety procedures listed above. Then find the air intake, for the engine, and block the air from entering the intake manifold. [You will have to remove the air cleaner/silencer, in most cases.] Use your hand, large rubber ball, and/or other item that would not be sucked into the engine when cranking. Have someone crank the engine and after several revolutions you will note that the rpm's will increase substantially. Remove the air intake restriction, quickly, and the engine will receive a burst of air that should force ignition.
  This procedure works on the basis that if the air is restricted from entering the cylinder, the engine cranks faster, because there is no compression taking place in the cylinder. (you have created an airless vacuum inside the intake manifold and cylinder, after a few revolutions) The burst of air that the engine receives after you remove the restriction is comparable to having a turbo-charger or ram-air device. A low battery and/or cold conditions may require several attempts at this procedure.
  If you don't notice a change in cranking speed with the restriction in place, either you haven't restricted the intake properly or you don't have compression taking place inside the cylinders in the first place.

Warning: Any flammable liquid and/or vapor in the bilge of a boat, if ignited, can destroy the boat and/or mortally injure it's occupants.

The  final desperate move... 
First, follow all safety procedures listed above. Then with someone cranking the engine, wait for the engine to obtain full cranking speed, then give the engine a 1/2 second blast of starting fluid directly into the intake manifold. (I had an old timer tell me that his wife's hair spray worked the same as starting fluid, but that surely was a desperate move.) Never spray near or towards starters and/or other sources of ignition. A low battery and/or cold conditions may require several attempts at this procedure.

  At this point, if you haven't hurt yourself and/or bent a rod on the engine, then the motor should be running. If not, you have a major mechanical problem that needs to be corrected. Toss out an anchor or start paddling.

Start over and go look at some of our tips.

Note: Never try these procedures unless you are completely familiar with all safety and warnings published on this site and in your service manual.

Good luck and be careful...  

M12, M15, M18, M20, M25, M25XP,
M30, M35, M40, M50
Typical Wiring.

"Volvo Penta Marine"  modernized their web site, recently. Their  extensive product line of marine engines, drive systems, and marine accessories is presented in an easy to navigate format. They offer full specifications and even installation drawings in pdf format. You could easily spend hours at this information packed site. Be sure to check out the customer service section.

And for those history buffs out there, they have an interesting  time machine page that goes back to the very beginning.

Web Note: The "open in new window" feature, when you click on a hyperlink, is used extensively throughout the new Volvo web site.

Note: The links above, open in a new window.

Volvo quicklinks: 

Engine database and publication search. [Free owners manuals]

FAQ at Volvo Penta

Volvo Parts Information

Pleasure boat engines   [open in new window/tab]

 As mentioned earlier, diesel packages for the marine industry have become more available and worth your consideration. "Yanmar" engine company teamed up with Mercruiser, a while back, to offer a diesel sterndrive package that was to become the market leader in it's class. However, it may have been one of the best kept secrets at the same time. 

Yanmar's small  one and two cylinder diesel engines are popular with many sailboat builders., though. This is a bulk of what's in the field in the US.

 Note: The link above, opens in a new window.

Maintenance videos for the Yanmar  YM, LP and BY engines

Links below allow you to view and/or download the Yanmar Marine maintenance instruction video.

Special Note: The Yanmar video information concerning fuel filter change unfortunately omits that you need to bleed the fuel system after changing the filter. Fuel system bleeding procedure is slightly different for each model they sell so, consult your owners manual.

" Cummins Marine"  For marine information including spec sheets, warranty information, service locator, technical application files, etc., Please note that you are not actually at cummins.com by accessing this link but rather entering a Cummins-approved web site.
There is also a joint web site between Mercruiser and Cummins where they have posted specs for their new joint venture. 

An interesting new joint venture, utilizing small diesel engines from Volkswagen, has yet to create much buzz. But, the rumor is that  Mercruiser just might eventually focus heavily on Cummins/Volkswagen diesel power over gas due to the "catalytic converter"  issues associated with gas marine engines. Stay tuned....

Note: The links above, open in a new window.



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