Diesel Fuel Maintenance

Diesel Fuel Maintenance. This adage “Give your Diesel Engine clean Fuel and it will run forever” is very true.

The RNLI, Sea Tow, USCG and many organizations will tell you that the most calls they get for assistance start by being engine related. They will also tell you that 90% of engine failures are due to Fuel issues. Bad Fuel is not a inconvenience issue its a safety issue.

Causes of Fuel problems

The two biggest ways to ruin a tank of fuel are;

  • water contamination
  • long-term storage

Water can get in Fuel so many ways, even if you get dry clean fuel, your tank system is vented (unlike a car) and the vent will let in humidity. Water also condenses on the tank walls due to temperature fluctuations, especially true in winter. The more air in the tank the more condensation. Its recommended that you keep your tanks up to 95% full to combat this.

Fuel sits on top of any water that will eventually settle to the bottom. Bugs can thrive in this water. You can kill these bugs with BIOCIDE? but you will still be left with their carcasses, which when disturbed in rough water can get to your filters. No water in the fuel no bugs or algae

Fuel clogging can be a problem. It always seems to happen at the worst time. You are in rough water and the motion stirs up the sediment in the tank and the filter gets clogged. You need to shut down the engine but you are in a nasty channel and need the engine.

Filling with the wrong Fuel. Gasoline in a Diesel Fuel system is disastrous and could involve the risk of explosion, so make sure the fillers say Diesel only.

Diesel Fuel maintenance

  1. Clean Fuel tanks
  2. Filter fuel as it comes aboard
  3. Keep Water OUT
  4. Stabilize Fuel that’s stored or sits idle
  5. Biocides kill bugs
  6. Dispersants separate water from Fuel
  7. Filter fuel before it gets to engine
  8. Polishing Fuel systems onboard


1 Clean Fuel tanks

Inspect your tank and if you have any doubts clean it.

Mobile services are available to clean your tanks. They are commonly known as Fuel polishing services. They come and pump the fuel in your tanks through a filtration system. This can give you clean Fuel at the beginning of the season.

Quality Yacht Services Marine Fuel System is a company based in Florida covering the Florida Keys, which is an example of a tank cleaning service. Check your local area for a similar service.

Here is an example of the type of unit they might employ from RCI Technologies.

The RC-PTCU.HV is a 60-gallon a minute portable contaminate removal system, designed specifically for the cleaning and transferring of fuel to and from above and below ground fuel tanks.

Utilizing the Blade Master self-adjusting, self-priming pump, with the proven RCI Technologies Purification unit to provide not only an efficient fuel transfer system, but also an efficient fuel cleaning unit to remove the water and other contaminates from all your fuel stores.

2 Filter Fuel as it comes aboard

Buy Fuel from a reliable source, that you can be confident in. If you have an source unknown to you check the fuel. Pour some fuel in a container and let it settle. Water and dirt will settle to the bottom. If you see either, filter the fuel before it goes into the tank, or better yet, buy your fuel somewhere else.


WM-F8C these filters from West marine were tested by Powerboat Reports (March 2003) and rated better than other more expensive funnels.

Teflon-coated, stainless-steel filter separates water and dirt from gasoline, diesel and kerosene fuels. Made from industrial standard electro conductive polypropylene that can be grounded for extra safety. Fuel flows quickly through the filter into the tank and water stays in the funnel. Practical-Sailor did a test and found it to be the best despite its low cost. $35

Baja Filter

The Baja Fuel Filter is housed in a cylindrical aluminum alloy canister that measures 4.5 inches in diameter and is 18 inches in total length. It is available with a welded 1.3-inch diameter spout or a 1-inch diameter spout.

Both spouts are 5.75 inches long. The filter weighs 3.75 pounds and has a maximum flow rate of two gallons per minute. It includes three filter elements (coarse, fine, water separator), spacer ring and cap set.

Fast funnel

Disposable funnel for spill free fueling or oil fill

3 Keep Water Out

H20 out
H20 out

H20 out

We know that if you leave a boat for a long period that you should fill up the fuel tank. This reduces the chance of condensation as there is less room for air. Air forms condensation and the water produced gets into the fuel.

One area where air and condensation can get in is through the fuel tank breather and vent line. This simple vent can let in moist air. You do see people stuffing rags into the vent fitting to stop moist air getting in.

To combat this problem, the h20 out from Pindell Engineering is a high tech filter that eliminate the moisture. The installation is simple as the fitting splices into the vent hose line.


4 Stabilize and Fuel Storage

Stabilizers provide stabilizing chemistry and are needed when fuel sits for extended periods. Fuel when left for a long time can separate often called phase separation. Fuel stabilizers can prevent phase separation.

Additive manufacturers are numerous, but some specialize in recreational marine needs and remain in the forefront of fuel technology.

StarTron Diesel Additive

Starbrite manufacturers of storage stabilizers for marine fuels. Star*Tron is an enzyme-based additive for gas or diesel fuels that solves a host of fuel-related problems.

Star Tron disperses bacteria, allowing the fuel filtration system to function efficiently. Prevents fuel oxidation and stabilizes diesel chemistry for at least two years. Eliminates moisture in diesel fuel by dispersing it to sub-micron size that can be safely burned off during the combustion phase. Because it treats water in fuel, Star Tron aids in fuel gelling issues; by removing the moisture, it cannot be converted to ice crystals at low temperatures that in turn can lead to fuel gelling. Also kills bugs.

Valvtect Marine Diesel Additive with BioGuard

This product is a stabilizer and has a biocide additive. Stabilizes your diesel for over two years, extends filter life, lubricates injectors and pumps, disperses water, cleans up injector deposits, improves fuel economy and keeps your clean fuel system free of bacteria.

PRI-D Diesel Fuel Treatment

PRI-D is a super concentrated; one quart treats 512 gallons, is a complete fuel treatment that improves all diesel fuels enabling them to perform to maximum potential. PRI-D’s industrial strength, enhanced thermal stability chemistry reacts with fuel upon contact, and provides multiple benefits: Engines perform better and last longer Increased power and fuel economy Fuel stays fresher longer Tanks and fuel lines remain free of slime and sludge


5 Biocides ( kill bugs )

When using biocides it important to remember the carcasses are left in the bottom of the tank. You have cleared up one problem but another is potentially still there so check your filters, clean the tank or polish.

BioGuard Fuel Microbiocide

Prevents Bacteria and Algae Growth Removes Excess Water Stabilizes fuel for up to two years Lubricates and cleans-up injector deposits

Biobor JF Microbicide        

Biobor® JF is a liquid fuel additive that combats fungus and other microtive life in hydrocarbon fuels, such as diesel and jet fuels, but is also effective in light oils and transmission fluid. Biobor® JF eliminates growth of harmful slime-producing fungi that clog filters and pipelines, attack rubber fuel system components and whose waste products aid in the corrosion of metal surfaces. Biobor® JF is simple to use and harmless to the wide variety of fuel system parts, top coatings, sealants and elastomeric materials tested. It does not adversely affect fuel performance in engines. Biobor® JF is an effective microbiocide because of its equilibrium solubility in both fuel and water under conditions of fuel storage.

StarTron Diesel Additive

Star Brite manufacturers of storage stabilizers for marine fuels, recently introduced Star*Tron. Star*Tron is an enzyme-based additive for gas or diesel fuels that solves a host of fuel-related problems.


6 Separate & Remove Water

Even pure diesel fuel will pick up about 5 percent (thats fairly high) water through distribution channels. Any container that holds fuel will have some humid air and will be a source for water. For this reason, water separators have been the chief line of defense for diesel engines.

c quip super soaker

CQip wins innovation award for its new Super Soaker a device bag type device that sinks to the bottom of the Fuel tank and soaks up water. The super soaker absorbs water from beneath the fuel.


Fuel Set Liquid is a complete fuel conditioner, which is claimed to absorb any water present in the fuel. Treats diesel, petrol and 2 stroke fuel, and is completely harmless and environmentally friendly, (made from natural compounds). It dilutes with fuel at a very economical 4000:1 ratio.

From Liquid Engineering; Emulsified Fuel; Water emulsion or water held in suspension can cause serious damage to fuel system components. The water content causes loss of lubrication resulting in worn fuel pumps and injectors. Emulsified water also reacts with chemicals in the fuel at the point of combustion, which causes contaminates such as gum, wax and resin to separate and foul fuel systems, especially injectors. Emulsified water can seriously degrade certain types of fuel filters.

7  Fuel Filtering

Fuel filtering and polishing are different. Filtering happens as fuel is supplied to the engine, polishing can be done at at anytime and fuel is fed to the polishing unit and then back to the tank, so its clean and ready for the engine.

Many boats have more than one filter between the engine and the tank. The filter on the engine is know as the secondary filter and the engine manufacturer expect that only very small contamination is going to get to this point.

The vessels primary filters do the most work and remove water & contaminates from the fuel. These primary filters should have clear bowls underneath., which make it easy to see what’s going on. You can drain the bowl when necessary.

Even with good filtering you can still get clogged filters and the engine can get starved of fuel and shut down. You will have to turn off the engine and replace the filter.

One way to get out of this is by having dual filters. A valve can divert the fuel from the clogged filter to a new one, while the engine is running. This allows you to change that filter underway, in case of another incident. The American boat & Yacht council, (ABYC) recommends a metal heat shield for these fuel filters because the heat from the engine can melt the plastic bowls.

MLS Fuel Purifier

The MLS Diesel Fuel Purifier from Mechanical Line Solutions creates a centrifugal force that “Spins the fuel. The centrifugal action is created by the fuel itself moving through the unit. When the fuel enters the unit the baffles in the system immediately induce a swirling action, which causes water and solid contaminants to separate out of the fuel. The contaminants sink to the base of the unit where they are retained –until purged. Purging is done by draining off the water and contaminant using the bottom valve until clean fuel is observed.

Racor; MAX-DUAL Fuel Filter/Water Separator

When engines demand heavy duty, high capacity water separation and fuel filtration. Features rugged, non-corrosive die-cast aluminum construction. Glass bowl for diesel fuel only.” MA” units have shielded see-thru bowls. A single valve on all of the double manifold “MAX” models isolates one filter/separator for service while the other keeps operating – this way, you can keep running while draining contaminants from the collection bowl or while changing filter elements. For double manifolds models order “75” series.

KTI systems; Filter Boss

Allows for two filters to be installed one online and one offline that either filter can be selected at any time. Built in fuel pump allows easy engine bleeding with or without the engine operating. Also allows filter bleeding and servicing, fuel pump can also supply fuel to the injector unit, if lift pump fails. ON-BOARD FUEL POLISHING can be done using the fuel pump and FilterBOSS system. See the installation manual for information.

Gulf Coast; Depth Type Filters

Depth Filters provide sub micron filtration which is better filtration than edge type filters and have much larger capacities than edge type filters.

The majority of wear in diesel engines is caused by particles smaller than 5 microns. Depth Filtration consists of a fixed matrix of fibers arranged in random fashion. They provide a large number of flow passages through which particles must find their way. The result of this arrangement is a broad pore distribution with the ability to remove many smaller sized particles, in contrast with the narrow pore distribution found in surface filters.


8 Fuel Polishing

Fuel polishing is perfect for the long distance cruiser. Basically you are continuously filtering the fuel in your tank. The fuel is pumped from the tank through a filtering system and returned to the tank. I have read reports of guys opening up their tanks and see them looking like new after a couple of years.

A polishing system is remote to the fuel engine supply. The polishing system draws fuel of the bottom of the fuel tank goes through the filtration process (spinning out water and sediments) and is returned to the same tank. The system can be run 24/7 if necessary and does not need the engine running.

When building a polishing system, its important to allow for easy inspection and changing of filters. When sizing polishing systems it seems larger yachts are turning over their tanks every 3 hours or so. That means the equipment you choose should be able to pump the full capacity of the tank in 3 hours. You can get vacuum gauges that will mount at the helm station to let you know about a clogged filter. PassageMaker magazine May/June 07 has a very good article on polishing.

Here is a diagram for a Fuel system on a custom Catamaran including a polishing system. The Owners of The Adagio Steve & Dorothy Darden are kind enough to put this on their site and share it with the cruising world.



Manufacturers of Fuel Polishing Systems

Gulf Coast

Gulf Coast supplies filtration systems for the Military, Diesel pickups, RV’s, the Trucking Industry and Marine environments.

Fuel polishing system for large capacities these units can handle 120 GPH or the next size up 240 GPH. The 120 GPH unit retails $4000 approx.


ESI Clean Fuel Systemâ„¢ products exist to prevent engine failure by filtering contaminants from fuel in the tanks before it cycles through the engine. ESI Clean Fuel Systemâ„¢ products are available in various configurations, and can be custom-fitted to your engine room. Shown above is the integrated filter model.

Reverso Pumps

150DC Fuel Polishing System

Reverso Pumps newly designed FPS-150DC Fuel Polishing System uses a Racor Turbine filter with a high-capacity Aqua Block II element. The system processes 150 gallons an hour and removes 100 percent of water and any algae buildup in fuel tanks to keep diesel fuel clean and reliable. Reverso Pumps also produces systems with Separate filters, including one that processes up to 500 gallons per hour.

If a filter becomes heavily clogged, it can create vapor lock, says John Napurano, president of Reverso Pumps, manufacturers of fuel-polishing equipment for diesel-powered yachts. If the filter is too fine, or too clogged, the amount of vacuum necessary to keep fuel flowing to the engine spikes and turns liquid into gaseous vapor with air bubbles, which can be as damaging for the engine as water in the fuel.



There are many steps we have discussed here. Do I need to do all these things?

The answer is no and not everyone needs a polishing system, but if you are powering across an Ocean its not a bad idea.

For the very minimal approach you should check your filters, stop water getting in the fuel and if storing for a long time add a Fuel storage additive.

Used Diesel Fuel system