Fuel's Paradise: Onboard Fuel Polishing

Fuel's Paradise: Onboard Fuel Polishing

Posted by BoatRx2 Admin on

sail magazine logo Featured in the February, 2017 issue of SAIL Magazine. 


onboard fuel polishing in sailboat tayana 42


Maintaining clean fuel should be one of the highest priorities on any vessel equipped with a diesel engine.  Detecting and discarding any badly contaminated fuel is always your best bet.  However, after having done your due diligence and sampled your tanks, there is no harm in adding extra filtration.

three lines to each tank

We have two 60 gallon fuel tanks, built of fiberglass.  Each tank has a stainless inspection port, a dipstick and (thankfully) three fuel line connections.  Two of the connections reach down about 1” shy of the bottom of the tank, and the other has a tube extending just below the top of the tank.  Each tank required connecting one fuel line ‘send’ and two ‘returns’.

The 2015/2016 winter aboard Eclipse, our Tayana Vancouver 42, was a busy one.  In addition to overhauling many of the systems onboard, we had pulled out our old Perkins 4-108 for a rebuild.  Having the engine out of the way allowed for a critical rethink of the fuel system.  I used this opportunity to install an electric pump driven polishing system that would improve the reliability of having clean fuel in the tanks.  In this context, the term “polishing” really just refers to the repetitive refinement of the diesel fuel by circulating it through an external filter.  This system also offers a few bonus features. Like the ability to move fuel between tanks, and the option to keep fuel flowing in an event where the primary filter experiences a blockage.  The electric pump also makes an easy task of priming the engine all the way to its injectors.

It only took a brief look at some of the polishing systems that are available off the shelf to determine that a homegrown approach would be much more cost effective than spending upwards of $3000.  It’s important to note that systems at this price point are slightly more complex than the dual filter setups more commonly found aboard many yachts.  Redundant filters are usually designed so that there is always a clean filter ready to go when the other clogs up.  The operator then just has to turn the lever on a valve to swap over to the opposite filter.  This should keep the engine running while changing out the clogged element (not an easy task in a big swell, next to a hot engine).  I hope that my DIY polishing system will continue to reduce, if not eliminate, the need for an emergency filter change.

Essentially, the polishing system consists of two filter housings, two manifolds, and many bits of hose, ball valves, low-pressure check valves and threaded pipe connections.  All parts were purchased from McMaster Carr, Ebay or Amazon.  I was sure to use USCG Approved A1 Fuel Hose from Trident along with proper non-perforated 316 stainless hose clamps.  Every connection was double clamped.  Threaded connections were sealed with liquid teflon plumbing sealant that is rated for diesel fuel.  I was also sure to use stainless nipples between any aluminum and brass connections to minimize galvanic corrosion.  Everything is secured to a large piece of starboard that required some creativity to mount in the engine compartment.

The most important component of this system is definitely the polishing filter.  This is where the magic happens.  I used an industrial style depth filter from Shelco.  The model I have is an FLD-78, in stainless steel, purchased on Ebay for about $100.  These are the same types of filter housings that you find being used under your sink at home to filter drinking water.  They are meant for a high volume of flow and can trap enormous amounts of particulate as compared to a surface filter like the type found in the Racor water separators.  These thick fiber elements look like a roll of toilet paper and are very inexpensive compared to their surface filtering counterparts.  Depending on the size of the housing you have, you can find filter elements for less than $6 each, and far less than that if you buy them by the case.  Just be sure to check that you are buying the type that is compatible with diesel fuel.  I chose a 10 micron filter which is sufficient for most conventional diesel engines.  If you have a modern engine with common rail fuel injection, you’re going to want to filter to 4 microns or smaller.

Like most projects, most of my time was spent researching and planning.  Full assembly took about 20 hours, but that was after a number of late nights on the computer doing research and putting my shopping list together.  This system is not perfect.  It cannot cleanse a huge load of bad fuel, nor can it clean thick sludge from the bottom of a badly contaminated tank.  It is however a great tool for preventing good fuel from going bad. 

A sheet of plastic Starboard was mounted in the engine compartment.  The white surface directly behind is the side of a fiberglass fuel tank.  My mounting options were limited.


Fuel that travels through the depth filter is then pulled through the 12 volt gear pump and sent to the output manifold.  Fuel travelling through the Racor continues straight through to the same output manifold.  It’s at this manifold that the operator can use ball valves to select which equipment can consume the fuel or where the pump should return the clean fuel to.  Options include both tanks, the main engine, or the onboard diesel heater.  I also included an extra port for a future genset.  Low pressure check valves are used on the tank returns to prevent unfiltered fuel from being sucked back through the return lines and into the engine.