By Bob Norson

We had waited for the strong wind warning to abate before working our next leg north. The S.E. had gone from 35 knots for several days, to near nothing. The way the season had been going there was no future in waiting around for good conditions; we would never make it north.
We reconciled ourselves to a 60 mile motor to Keppel Island. The howling trades were gone, but the huge swell they had generated was still around. It was a roller coaster ride all day, with the swell on our stern quarter. About ¾ of the way there, the motor started doing strange things. The RPM was rising and falling in a rhythm similar to the swell.
Our old Perkins 4236 is a very reliable thing, and we were particularly depending on it that day. It got us to Keppel…just!
The anchorage was rolling heavily, but work had to be done. The glass bowl on our Racor filter showed some debris, but not horrid. Opening the top however, was impressive. The filter element was buried under a thick brownish goo. I don't know how it ran at all!
With the housing cleaned out, a new filter element installed in the Racor, and the Lucas filter downstream, we were in business again after bleeding the lines.
Sound familiar? Ours was a typical situation. Our tanks were full of “THE BUG”. The rough sea conditions stirred the mess up, and soon we were in trouble.
Our vessel has everything going against it for keeping diesel clean. She carries 2000 litres in two steel tanks. Needless to say, our fuel sits for a long time before use. In spite of all, we seem to be winning. It has taken some research and work, but if ours can be cleaned up, anyone's can!

Over several years we had usually used a common fuel treatment that was easy to get. In spite of it, our fuel was getting darker, and I was changing filters more and more often. It was time for drastic action!
Since most of the fuel we use is (Brand Z), I gave their distributor a ring. They organised contact with their laboratory. The lab sent up a couple suitable shipping containers and I sent them back with samples of our ugly fuel.
A week or so later, I got a call from the laboratory. Our fuel was alive with “the bug”, and heavily oxidized. Overall, not good. He asked what treatment we used. When I told him the brand most often used, I could hear the groan. With special emphasis he said, “We do not recommend that type of treatment.” He went on to explain that that treatment was an emulsifier. It caused the moisture in the fuel to become “suspended”, which he explained, is the ideal environment for the bug. He preferred a treatment that allowed the moisture to separate, and that contained a strong biocide. “Fuel Treat” was one of the brands he thought was effective. “So which one is best,” I asked? “I’m not really supposed to say but... Fuel Treat is what I would use,” he offered conspiratorially.
The technician was very patient as I interrogated him to learn all I could to cope with the diesel fuel storage problems. Here is some of what I worked out:

If your filters have a glass bowl, check the appearance of the fuel. Ignore the colour for now. Look at the clarity. If it's difficult to get a good look in your engine room, dip out, or pump out some fuel from your tank into a glass jar. Get it from the bottom of the tank if you can. Simply compare that with some fresh fuel in a similar glass container.
If the clarity is similar, you probably don't have “the bug”. If your tank sample has a cloudy look to it (even slight), you probably have “the bug”.


Compare colour and odour. Different suppliers may have a little different colour, but if there is a great difference along with a “stale fuel” odour that the fresh sample doesn't have, you may have oxidation of the fuel.
If you have tanks in perfect condition, use your fuel regularly, keep the tanks topped off, and are lucky as hell, you might be OK. For the rest of us, a good treatment like FUEL TREAT BC250 is the go.
Follow instructions carefully. Just pouring a dose in the tank doesn't work as well. I mix a dose with a half full 25 litre drum of diesel and shake like buggery. Then pour it in just before topping off.

Now that you've cycled through some good biocide and your fuel is nice and clear, your clogged filter problems are over…right? Not necessarily!
The dead remains of the bug, and all the other crud that's contributed to your tank pollution is still there. The goo is just waiting for you to cross a bar in bad weather, or some such thing to punish you for your optimism.

Subaru's of mid-eighties vintage, have a good electric fuel pump on the 4x4 wagons. If your local wrecker doesn't have one, a variety of electric fuel pumps can be purchased at any auto parts store.
I bought a spare Lucas diesel filter assembly, with glass bowl water separator, from a marine supply for about $90 plus some spare filter elements. I also fabricated a settling chamber using a glass jar with a couple bits of copper tube, epoxy glued through the jar lid. The longer tube is the input. The shorter tube takes fuel off the top, leaving the worst of the muck to settle on the bottom of the jar before sucking it through the filter.
I put everything together with about $20 worth of 10mm copper tube, vinyl hose and fittings for the filter body.
Fuel is sucked out of the bottom of the tank, or wherever I placed the copper pick up tube, pulled into the ‘settling jar,’ through the filter, then the pump, and finally returned to the tank via vinyl hose.
The fuel pump takes very little power and we have solar to top up the batteries so, when the boat was in harbour I let it run for days at a time. I understand there are now services available with high powered pumps to do all this in a short time. The Americans call this “fuel polishing.”

It was three years ago that our fuel was analysed, and our treatment with BC250 began. Since then I have also used the Fuel Treat anti-oxidiser. After cleaning up the tanks I have had no reoccurrence of the problem.
Our fuel is clear and we have had no filter clogging or mechanical problems. Our old Perkins has run perfectly with exhaust smoke at a level with a new engine. Since we use only about 400 litres per year of our 2000 litre supply, I believe I qualify as an expert in fuel storage!