Keeping Diesel Fuel Clean

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Seems like whenever I am on a cruising boat, there is some discussion of the boat's fuel system. For those of us who cruise in trawlers, our engine is the very heart of our boats. More so than any other component, the diesel engine is our single most important piece of machinery. On single engine boats, especially, the engine is the most well cared for piece of equipment. And for good reason. If we lose an engine for whatever reason, our day on the water is not fun.

The single most common cause of engine failure is fuel related. (I have it on good authority that the actual number is 93 percent of engine failures. More on that to come later for subscribers.) Water in the fuel, contaminants in the fuel or tanks, microbial growth in the tanks, and air leaks in the fuel delivery system all become potential issues if not dealt with properly.

And for crying out loud, will people PLEASE stop calling these microbial organisms ALGAE!!! This microbial growth is not algae, never has been and never will be. Algae requires sunlight to grow. Yes, I know there are products out there with "Algae" on the label or company brand. Trust me, stay clear of anyone telling you a different story or trying to sell you snake oil products. It is bacteria and fungus that live and grow in the biomass layer that interfaces between the nutrient-rich diesel fuel and any water standing under it.

And the bacterial sludge one might find at the bottom of a fuel tank is a combination of dead microbes, asphaltenes, and particulate matter. If sea conditions stir up the fuel in the tank, this nasty junk, once in suspension, will clog any filter in no time and kill the engine. But it is not algae.

Which got me thinking about a subject I still don't quite get why people are so easily confused. Fuel recirculating or polishing. I've seen countless threads where people go on and on about filter filtering versus fuel polishing, some even quoting me from a past seminar or article on fuel systems and fuel polishing. There are very specific criteria that must be precisely met for a proper fuel polishing system to be anything more than just another way to filter fuel. Use a low volume pump and you do nothing but run diesel through a filter then return the clean fuel back into a potentially dirty tank. Use the wrong size fuel lines that restrict flow from a pump that may be 180 GPH, and you will not see results. Put pickup and return pipes in the wrong locations or too short in a tank and you also don't perform the intended goal. Even the shape, construction, and installation of the tank is an important consideration.

Leave out even one of these key design and installation elements and you do NOT have a system capable of stirring up the contents of a fuel tank, filtering out 99.99% of the water and 100% of all particulate and microbial contaminants. And the system must run long enough to cycle the fuel several times worth the full tank capacity. But of course, you must start with clean fuel tanks, as there is no way any system can magically clean the gummed up sludge and asphaltenes covering the bottom of a tank after years of fuel sitting for long periods of time.

But if you start with clean tanks and religiously use a properly designed and installed fuel polishing system on a regular basis, your tanks and diesel fuel will remain clean. I know this because, after participating in a dozen years of fuel system seminars (at TrawlerPort, Trawler Fest, and commercial industry events), and many articles, I know this to be true...especially after owning Growler. Even Steve D'Antonio became a believer once he saw the results firsthand.

BTW, since I am talking about fuel, I'd like to share how amazing it was to participate in seminars with panels of engine experts, talking about things like filter issues and element sizes. I believe it also explains why there is so much discord and misinformation offered on internet forums and social media threads. If you ever attended one of our many seminars, you know we worked hard to get real deal engine guys, usually crusty characters who spent many years turning a wrench in an engine room before going up the company ladder to advisory or management positions. Lugger, Deere, Cummins, Cat, Yanmar...doesn't matter. 

When it comes to diesel engines in powerboats, these guys are used to thinking in terms of motoryachts and sportfishing machines that carry large amounts of diesel fuel, and turn that fuel over in a relatively short time. During a billfish tournament in the Carolinas, for example, these huge sportfishing yachts can go through a thousand gallons in a couple of days. Trawlers are so completely different. Yes, we also have significant fuel tankage, as much as 300–3,000 gallons or more, but our propulsion systems are designed to burn fuel efficiently, at much slower speeds. Consequently, we enjoy good fuel economy and long range, which creates somewhat of a unique fuel management situation that other boats don't have. We store a lot of fuel in our fuel tanks for long periods of time.

In some of these seminars, you could almost see the moment where there is a shift in understanding, as some men start to get for the first time that our issues are different than what they are used to, and that the potential problems we try to avoid are unique to our lifestyle. And that the mechanical engine technology they learned back in the day no longer fits the reality of emissions regulations and modern common rail engines. Our electronic engines require exceedingly clean fuel to avoid injector wear, but our large fuel supply (and longer term storage) is an environment that works against keeping this fuel clean. 

It was always kind of cool to see a guy come around and admit to our issues, although perhaps not quite as dramatic as that story when the skinny-tied, '60s NASA engineers realize the brilliant mathematician, a young black woman, just smoked their theories out the window...

Having clean fuel is essential to safe and reliable cruising. Nothing else is as important for your diesel engine.

Having clean fuel is essential to safe and reliable cruising. Nothing else is as important for your diesel engine.