The Blue View - Polishing the Fuel

baja filter  

In our early years of cruising, we learned the hard way about how important clean fuel is. I didn't worry about the fuel as long as the primary fuel filter looked clean. On one offshore passage, however, the seaways were a bit rough which churned the fuel enough to mix up all the sediment that had been lying benignly in the bottom of the tank. As we motored into a tight marina full of very expensive boats, I discovered how quickly the fuel filters could clog up, starving the engine of fuel. The old adage about aiming for the cheapest boat came to mind, but fortunately we managed to secure a line to a t-dock before damaging anything other than our pride.

As soon as we could, we hired a service to clean the tanks and polish the fuel. There was nothing magical about the process. They simply pumped the fuel out of each tank, processed it through a rather large industrial version of a marine diesel filter, then discharged it into another tank. They cleaned the inside of my tanks with a wand, and pumped the fuel back in, all for a rather outrageous price.

Since that expensive lesson, we have been a lot more careful about our fuel, and do what we can to prevent getting contamination into the tank. Our first line of defense is our old reliable Baja filter. We almost always use it when refueling at a marina or fuel dock. This increases the time needed to refuel, however, and there are times when the attendant gets a bit cranky when we insist on using it, especially at a busy fuel dock. Usually we can reach a compromise by using the filter for a minute or two, then doing a quick check of the filters to see whether we are getting water or other contaminants. Only once has an attendant flatly refused to allow us to use it.

Even with the best of precautions, however, we still get water in the fuel tanks. I have replaced the o-ring on the fuel cap, thinking this might be the source, but that didn't eliminate the problem. I suspect it comes from condensation forming inside the metals tanks as the ambient temperature varies. If not removed or treated, the water will allow algae to grow, which in turn will clog the filters. To combat this, I built a small fuel polishing system and routinely clean the fuel and tanks. While not my favorite chore, it isn't difficult and I do this annually, or any time I see any signs of sediment build-up in the primary filter.


refueling in the panama jungle


As we travel to more remote areas, fuel docks become rare and “jerry canning” is the usual method of obtaining fuel. The photo shows a fuel station in the Darien Jungle, up a Panamanian river. Another notable instance was in Ushuaia at the southern tip of Argentina, where fuel was rolled down to the dock in rusty 55 gallon drums. We were rafted up with four other boats between us and the dock. The process was to carry empty eight gallon fuel cans across the other four boats, siphon fuel out of the rusty drums, lug the fuel cans back one at a time to Cups, and decant them. After repeating the process for a total of 26 trips, I was definitely ready for a beer.

When I decant diesel from fuel cans, especially when it is as suspect as that fuel in Ushuaia or Panama, I usually use the fuel polishing system to transfer the fuel. It is a bit slower than the Baja filter, but eliminates any chance of spilling fuel, and is probably more effective in removing contaminants and water. In addition, the Baja filter must be cleaned after each use, which takes about 15 minutes and is messy, while the fuel polishing system requires no cleaning after use.

The polishing system is quite straightforward as shown in Figure 1. The intake is via a wand that is long enough to reach to the lowest point of the fuel tank. I used stainless tubing for the wand, but PVC or aluminum tubing would work just as well.


block diagram


This is connected to a Racor diesel filter. Any quality automotive or truck diesel filter will work, but I like the Racor Turbine Series with a clear see-thru bowl. I had a spare Racor onboard, but if I didn't already have it, I would expect to pay $180 to $200 online for a Racor 500 series filter assembly and about $8 to $10 for each filter.

The outlet of the filter is connected to an electric fuel pump. I found this at an automotive parts store by asking for a small universal diesel fuel pump. The least expensive one I found was $38.00, and this included a mounting bracket and hose fittings. The fuel pump is connected via a switch to 12 volts. I use a standard 12 volt plug for the connection.

I mounted everything on a piece of plywood to make it portable. That way, I can use it for either of the fuel tanks below, take it up on deck to decant fuel from the fuel cans, or even loan it out to other cruising friends with fuel problems. I use a bolt inserted into the discharge hose and clamp, and clamp a short hose with a similar plug to cap the intake wand. This seals the system when not in use.


fuel polishing


To polish the fuel, I try to plan ahead and wait until the fuel levels in the tanks are less than half full. I remove the inspection hatch from both tanks, insert the wand into the one, the discharge hose into the other and start the pump. To begin with, I position the wand so that it is an inch or two higher than the lowest spot in the tank. I monitor the fuel rate and water level in the filter bowl. The water can be drained from the bowl periodically as necessary, and when the fuel flow begins to slow down, I change the filter. When the tank has only an inch or two of liquid left, I get a flashlight out and take a look at what is left. If it looks relatively clean, I continue pumping the tank as dry as possible, then get a bucket and sponge out whatever is remaining. If it is mucky, or there is a lot of debris or water remaining in that last inch or two, rather than consuming two or three more filters, I sponge out all the remaining liquid, muck and sediment. Next, I wipe the entire inside of the tank with rags or paper towels. Hopefully, one tank will hold all the fuel. If not, I use fuel cans to hold the excess.

Next, I repeat the entire process on the second tank, pumping it back into the first tank. Again, I sponge out whatever remains in the bottom of the tank and wipe the inside of the tank. Lastly, I dispose of the bucket of muck in a responsible manner.

The entire cost of the project was about $150 (~$350 if I didn't already have the filter), and it rarely uses more than one $10 filter to polish both tanks. This is less than what it cost to have our fuel polished the one time by a service. In addition, I use it frequently for decanting diesel from my fuel cans.