Tuesday 10 January 2023

How We Kept Our Fuel Clean

 Fuel Polishing

Clean fuel, because motors don’t run properly on the dirty stuff. Working offshore I got to see a lot of contaminated fuel. The sources of contamination were from a variety of sources but the most common was water in the fuel from condensation or poor transport. On Matilda I was a little paranoid about dirty fuel and would regularly dip the tanks and pump out a small sample from the deepest corners of the tanks on a regular basis to check for any contaminates. We normally treat our fuel tanks and storage cans with additives to help keep the fuel bug in check, however it’s always a good idea to keep an eye out for developing problems and test for contamination. I must admit we never have had a problem with condensation, perhaps its luck or if its the epoxy tanks.  

Hauling fuel in jerry cans, some times we didn't know what surprises we would get until back on board. You need to get rid of the foreign objects before the fuel goes into the boats tanks. 

Fuel sample apparatus, a outboard fuel bulb some 5/16 fuel line and a length of copper tube. The copper tube allows me to direct the tip into the deepest part of the tank.  Remove the 3/4" plug from the tank top and insert the tube and pump out a sample into an inspection container. 

I am not sure who came up the term to polish fuel or fuel polishing, I don’t see it as polishing but more like decontaminating the fuel. Anyhow, whatever you want to call it, fuel tanks and with it fuel maintenance is overlooked by a lot of cruisers.

It was during one of our earliest trips up the Queensland coast we had first hand experience of what happens when simple fuel tank maintenance is overlooked. We were holed up in Port Clinton to wait for a serious blow to abate. This gave us time to get to know some of the others stuck there and compare our travel plans.

One couple we knew from our local yacht club planned to travel up to the lower end of the Whitsundays. Seeing as we were headed to the same places we decided to travel together once the blow was over. Finally the blow reduced in strength but the seas were still lively and a little choppy. Time to make a move in the morning. We had hardly done many miles motoring out over the shoal bar entrance of Port Clinton when our traveling companion called over the radio to say he had a problem with his engine. It kept stopping. After talking him through some trouble shooting over the radio, he changed his fuel filter. 

They were back in business, but sadly this was short lived. It wasn’t long before he changed yet another filter. It was the same story, the filter was jammed with debris. The short story is that after another filter change, his spare filter supply was dwindling and rather than run out he eventually turned back. After waiting a couple of days the winds turned in his favour and the seas calmed so they were able to make a run down the coast to the nearest marina. As it turned out he didn’t have a fuel bug it was the accumulation of muck in the bottom of his tank stirred up by the lively sea state. The sediment had more than likely built up over the years and settled into the lower corners of his fuel tanks. Once in the seaway the sediments were disturbed and tainted the fuel in the tanks, clogging the fuel filters in a short time.

Before and then after with very dirty fuel, not a good situation


Debris can clog fuel lines before it actually makes it to the filter. This isn’t easy to deal with in a seaway. On one such occasion I have seen a length of clean hose fitted to a hose barb allowing the blockage to be cleared by blowing air (like trumpet playing) and in turn the debris back into the tank. Much easier than dismantling the fuel line one fitting at a time looking for the blockage. However, if purging the fuel line with air doesn’t work then unfortunately looking for the blockage one fitting at a time is the only way to do it. Keep in mind the 50% rule, divide the fittings/job in half and if the blockage isn’t there go half way back or forward again.

Even with a water separator filter on your fuel line, if there is just too much water in the fuel, it can get past the filter that most sail boat owners have. Large system filters (think big power boats) sometimes have a check valve that cuts the flow if the water reservoir is full. Other high flow systems use a form of centrifugal water separation and bleed off the water automatically. Always check the sight bowl in your systems filter bowl for water at the end of a day; check it several times a day if motoring a long time in order to catch a problem before your engine is damaged. Sludge and debris can clog a filter in no time, causing your engine to just stop, however water getting past the filter can do unrepairable damage.

Fuel transfer funnels, we have a very expensive one in the cockpit locker. We don’t use it any more, in all honesty it’s not easy to use while on board. It’s very hard to contain the by-products and clean the fine gauze filters after use. The other drawback is if you do see water entering the funnel the water trap is not fool proof for large amounts of water. However, don’t let my experiences stop you, just remember they are messy to clean up after use.

The other thing we don’t like about funnels and tipping fuel cans to pour, is small drops of fuel spit on deck due to the glug glug of the fuel leaving the can. To help keep fuel spillage to a minimum get a syphon jiggler hose, these are easier on the back than pouring fuel from the jerry cans into a funnel. To speed up the process use a 19mm hose version, transfer time can be less than tilting the can.

If you have fuel bubbling back up the filler hose when refilling the tanks, check the fuel tank breathers are free to let the tank breath. We have found the mesh used in the breather to keep the bugs out can start to corrode and block off the air. Treatment with an acid (vinegar) and stiff brush can work, however if this fails replace the breather head.

Some vessels have a gauze filter on the end of the pickup tube in the bottom of the fuel tank. This can be a real problem if it becomes clogged with debris. The tube needs to be removed to clean the filter. How the tube is held in place will vary by tank manufacturer. It may be a simple clamp or the tank inspection hatch will need to be removed. Not ideal in rough weather. 

Why and When to clean Your Fuel?

Why? We want and need a reliable engine. We have been in a developing close quarter’s situation with large ships and have experienced being washed toward a lee shore by a sudden storm. We need to know that when we turn the key to our engine we don’t have any problems. We also don’t want to have to pay for repairs to our engine due to damage done by contaminated fuel.

Indicators fuel cleaning is a good idea.

When? If your boat has sat for a while in a humid climate, particularly with day/night temperature swings
Travelling through Asia
A new to you boat
A boat that hasn’t been used recently/ regularly
Noticing that the fuel cap was loose and water/dirt may have entered the tank
Cleaning the deck with a high pressure washer has been known to force water into the fuel tank filler/breather
Someone mistaking the water and fuel fills and putting water in the fuel
Taking a wave over the stern (or place of fuel tank breather) and getting sea water into the tank
Getting a load of bad fuel. Bad fuel normally is fuel contaminated with water and in some cases water containing microbes that have started to multiply.
Other sources of bad fuel are heavy contamination with dirt or dust
Discovering an abnormal amount of water or debris in your primary/water separator bowl or secondary fuel filter
Basically the build-up of sludge, microbes and debris
Last but not least before going out in lively sea conditions

Keep a lot of these on the boat, we had 10 of each just in case, crazy perhaps, it all depends on where your at. 
As our friend experienced, the immediate problem is that your engine won’t run. While not damaging your engine, it is the sludge and debris that will block the flow of fuel causing your engine to starve for fuel, cut out and not run. Water, if you get water through your filter into the fuel lift and injector pumps it can cause unrepairable damage to the fuel system and components. Microbes can cause similar problems to sludge and debris, you will have to remove the by-product of the microbes as well as killing them and removing them from the tanks.

As a side note, the use of high pressure cleaners can cause problems if the fill caps are in the path of the cleaner nozzle. Depending on the brand of cleaner the pressure out of the nozzle will and has been known to over whelm the sealing ability of the fill cap seal/oring. The most versatile category of pressure washers, those ranging output pressure is from 2,000 to 3,200 PSI, so be careful when wielding one of these. 

There are a couple of ways to clean fuel.

First is to pump all the fuel out of your fuel tank through a filter system into clean containers. Going one step further with this process should be to open the inspection hatch when the tanks are empty then physically clean the tank walls. How much you can clean will be determined by the baffle system in your tanks. If the inspection hatch placement was logical it should be over the deepest recess of the fuel tank. The debris and water will/should settle into this low point and cleaning out the foreign matter should be relatively straight forward. Once the tank is clean the fuel that had been pumped out previously can be pushed through a nice new filter one more time back into the tanks.

Second, if you’re satisfied you don’t have heavy contamination of debris and water, set up a closed loop system and pump the fuel from the tank through a filter then back into the same tank, this process is the easiest. We use a system like this from time to time as a maintenance clean. We use a copper tube as a pickup wand to get into the lowest part of the fuel tank. We don’t need to remove the inspection hatch, we just remove the plug normally used for dipping the tanks to take a sample and insert the copper pick up tube. Don’t be tempted to use the fuel pick up line to remove debris as it won’t get to the bottom of the tank where the debris and water will be out of reach.

Tools Needed to Do It Yourself

Rags, paper towel, pump and filter assembly.

Our simple setup, fuel lift pump and a water trap and pleated element filter. 

First up we set up a bucket lined with a heavy duty bin liner, this is used as a rubbish bag to contain fuel and sludge from the filter housing and old filters. This lined bucket is a great place to dispose of rags and paper towel.

If you intend to empty the fuel tank you will also require sufficient containers to hold the contents of the largest fuel tank. Jerry cans are great and you may be able to borrow some empties from friends. Or if you have large tanks purchasing or renting a 200 litre drum or two could make it easier in the long run. Keep in mind, before putting fuel in any other containers check in-side them and make sure they are spotless and dry.

Whatever you use, you have to have sufficient containers to be able to remove all of the fuel from one tank at a time. You could transfer the fuel from one tank through the filter and into another if you have an empty tank. You may want to pop in a small amount of fuel and clean the empty tank first.

How to Do It

Will depend on your situation and the severity of the contamination.

The first thing we do before hooking up the electric/pump filter system is, to use a hand pump to test for and remove the water from the bottom of the tank. I remove the plug in the fuel tank inspection hatch to gain access to the tank through the sampling hole. I use a copper tube that reaches the deepest part of the fuel tanks, I connect a hand pump to the copper tube placed in the tank. This hand pump is a squeeze bulb as used to prime outboard motors. I have found this will quickly remove the water in no time (unless someone mistook the water and fuel fills and partly filled the tank with water). I simply pump the first samples into a bucket or large glass jar to get an idea of the water content. I then stop when I see only fuel is be drawn out of the tank. The reason I use this hand pump is to save on the use of fuel filters. If I was to just hook up the electric pump it could overwhelm the water separator and ruin the filter and not remove all the water.

Once we are satisfied the water is under control I connect up the electric/pump filter system. Then depending on the type of clean I let the pump run, cycling the fuel through the filter to remove it all from the tanks. Then once I am satisfied the tank is empty I will remove the inspection hatch and remove any last sludge and contaminants from the tank. Then I will wipe the interior of the tank walls with clean cloths and replace the inspection hatch. After a filter change on the pump unit, pump the fuel back into the tanks. Top up the tanks to full and treat with a biocide.

If I am doing a simple maintenance clean I will top up the tanks to full and treat with a biocide. Then I will remove the plug in the tank access hatch and insert the copper tube pick up. The output of the filtered fuel is passed back into the deck fill or through the access hole in the tank hatch. Once set up I leave the unit run for 6-8 hours. During that time I will regularly move the copper tube around in the bottom of the tank to ensure I have stirred up any remaining sludge. If I am removing all the fuel to gain access to the bottom of the tanks through the inspection hatch I don’t normally move the pickup tube. I do the clean up once the tank is empty and I have access through the inspection hatch.

Our fuel pump and filter system, isn’t a high speed process

We have made a fuel cleaner using a small fuel pump, water separator filter, the set up also has a pre filter (gauze filter) to catch large debris before it enters the fuel pump. Other components consist of a mounting board, fuel hose, clamps and hose barbs. We have a friend who copied our unit and used a large plastic chopping board to mount all his components on. All the components other than our copper tube pick up were purchased at our local auto spare parts store. I don’t think it really matters which store, they all appear to sell components to set up a system like we have. My previously mentioned friend sourced all his bits and pieces while in Asia and in his words said “it was interesting trying to explain what I wanted but the parts were there”.

If you want to build a pump and filter assembly check the filter unit you purchase can handle the flow rate of the pump you intend to use. High volume pumps require large filters capable of handling the flow, usually the higher the flow, the larger the components, the flow on is the space needed for storage between use.

Fuel pumps have to be capable of pumping hydrocarbons and there are only a few high flow pumps that will work. The pump we use isn’t the big high flow unit but the good thing is it is self-priming which saves a lot of mess trying to get the pump working.

The first time we used our unit I was drawing (sucking) the fuel through the filter. There are different trains of thought with this, the filter manufacturer said we should push the fuel through the filter. However, most boats and cars for that matter draw the fuel through the filter although it does depend on the filter type and setup. The gauze pre filter is a must, and best of all the housing can be disassembled for cleaning, tapping the contents into the previously mentioned bin liner and bucket. This pre filter has been important when there is large contaminates in fuel we have purchased. Sometimes during refuelling the gauze filter has become blocked 3-4 times just transferring a 20 litre jerry can.

Gauze prefilter, here you can see the small black balls of contaminants trapped.

How is this level of contamination possible you may ask, while traveling through Asia we have purchased fuel from vendors who have open top 200 litre drums stored in a thatched roof shed at the back of the property on a dirt floor. The fuel is scooped and measured in a large ladle, we have had fine saw dust, dust, insects and very occasionally a little water. However, we do know others who haven’t used their own fuel cans and have had high levels of water in the delivered fuel. I don’t believe its foul play but how the supplied cans are stored between uses. The difference between fuels supplied in Australia to those supplied OS is immediately noticeable.

This isn’t a hard project to either make the pump and filter unit or do the job. Keep in mind once you have the unit made it doesn’t take long to set it up. We store our unit with plugs in the end of the hoses to prevent any spills while in storage.

Our setup, 12v lift pump a water trap filter with an pleated element filter, all mounted on an acrylic board (plywood would work) . 

While this all sounds easy the one thing I didn’t mention is that some fuel tanks do not have large inspection hatches. This can be a problem getting access to remove the muck in the bottom of the tank. Picking up the smaller bits of debris isn’t hard by simply injecting in additional fuel to stir up the muck while also running the filter unit works. I know a couple of people who have removed their fuel tanks and stood them on their end having the accumulation of muck go to the lowest part of the tank for removal. While all this sounds good we also know of another couple who had to have inspection hatches installed into their fuel tanks. The by-product of a fuel bug was so gluttonous that it could not be dealt with through the small tank access plug holes. Finally the only way to remove the muck was through the newly installed inspection/access port. Due to the large variety of materials used to make fuel tanks this may not be an easy job and may be best left to the professionals. Fuel leakage from the fitment of inspection ports is a real possibility if the job isn’t done correctly.

Fuel tank inspection hatch on Matilda, material for the seals can be brought from good gasket material sellers. Make sure it is nitrite, and from our experience this is available in a various sizes and thicknesses the one we bought was off the roll at 1.2 metres wide (4' in the old money) 

Once your fuel and tanks have been cleaned up, it’s time to do preventive maintenance. Dip the tanks and take a sample from the bottom of the tanks on a regular basis. What is a regular basis? At the end of the season, so four times a year. If you discover water in the tank you will need to investigate how it got there. If its condensation there shouldn’t be much water or sludge in the tank. On the other hand if there is a severe contamination then it will be time to search out why. If you haven’t taken a wave over the stern or where your tank breather is, then perhaps the deck fills are not sealing. There can be a multitude of reasons and it may take time to get to the bottom of the problem. Top up the biocide with every fuel fill, does it work? I don’t know anyone who uses it that has had a problem with fuel bug.

Filtering fuel on into the boat after a fuel run, its a bit slower but we found a cleaner option and removed the contaminates before they got into the tank. 

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