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Dealing With Dirty Fuel

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dirty fuel
Changing the Racor element


Bound for the Windward Islands from the Bahamas, perhaps via the Dominican Republic and the Mona Passage, you’ll often find the subject of dirty fuel at the top of the agenda over those keenly awaited sundowners.

It was mid-March. We’d dawdled too long in George Town and on the pristine beaches of the Exumas and missed the best weather windows. Most likely we’d be motor-sailing and we soon found we weren’t the only ones as we fell in with a group that was taking the same route.

Several boats had problems: fuel problems. Leaving the land of the free, where fuel at the pump is always clean, it is perhaps easy to forget that elsewhere this isn’t always the case. So what can we do to deal with dirty fuel and minimize the risks of the engine stopping just when you don’t want it to? And how can we deal with it quickly and get going again if it does happen?

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dirty fuel
Using the Baja filter and siphon tube

Before we blame the bad fuel on dirty Pedro’s contaminated fuel truck, a bit of general housekeeping. Even the cleanest fuel will leave a little sediment in the bottom of your tanks over the years. Pottering up and down the ICW – no problem. Once you’re out in the ocean it all gets stirred up and that nice clean fuel is now dirty.

Fuel tanks need cleaning. If you have a big enough inspection hatch you can do it yourself. Reach in there with some rags. If not get it done professionally before you leave. Know the state of your tanks.

dirty fuel
My modified siphon tube – note the rigid section just the right length to suit my jerry jugs

Here’s a couple more tips that will help you manage your fuel. Buy a jiggle siphon tube, it makes filling the tanks from jugs a piece of cake (Amazon sells them for around $10), and a filter funnel to filter the fuel as it goes into your tank. A ‘Baja’ diesel filter is best if you can find one or at very least a water separating diesel filter funnel.

The next step is to ensure the fuel you put in your tanks is as clean as it possibly can be. If you’re suspicious for any reason at all (which you should be) don’t dive in and fill those 100 gallon tanks. Just fill a five gallon jug; let it stand for a day. Use your new jiggle tube and filter funnel to slowly siphon the contents of the jug into the tank, but make sure the jiggle tube sucks from a couple of inches off the bottom of the jerry jug and leaves behind any dirt or water that may have settled. Now look into the jug and inspect the dregs and decide if the fuel is acceptable or not. If all looks good then you can perhaps consider filling your tanks directly; if not then maybe there is a better source.

dirty fuel
Essential spares – Keep it clean, keep it running

I always add a biocide to prevent microbiological growth, something we should all do especially in warmer climates. Biobor JF® seems to be the most readily available and does the job.

Once the fuel is on board there are further things you can do to stop dirty fuel causing problems. If you have more than one tank you can use the biggest as the storage tank and the second as the ready use tank, which should only be filled from the storage tank via a transfer pump and a water separator/filter. Or you can ‘polish’ your fuel by installing an additional transfer pump and a water separator filter assembly to re-circulate the fuel. This both cleans the fuel, eliminates any water and generally keeps the tank in good shape.

Moving on to the actual engine feed system there should be at least one primary filter / water separator. The ever popular Racor 500 series filter with its internal element is the best choice for a primary filter if only because of the ease and speed with which you can change it. Replacement elements are cheap and available

dirty fuel
Installing a primer bulb make life easier

everywhere. There will be at least one secondary filter as fitted by the engine manufacturer. I like to use a fine 2 micron primary filter, which though it may need replacing more frequently protects the secondary filter(s) which are often more difficult to service quickly. Change the primary filter element at every oil change and the secondary every year. That way it becomes part of your routine maintenance.

If after all these precautions you are still unfortunate enough to get blocked filters it’s good to know you can change the element quickly.

To make things easier install a primer bulb just before the Racor, just like the one in your dinghy. It will make priming the filter and bleeding the fuel system painless.

If the engine does die, open the top of the Racor with the T handle, gently lift out the dirty element and lower a new one in. Slowly pump the primer bulb to fill the housing right to the brim. Carefully change the O-rings on the T handle and the lid and reassemble. Less than two minutes and you’re good to go.

Following these simple procedures will serve you well wherever your voyages take you.


Sim Hoggarth is a British merchant navy marine engineer now cruising in the Caribbean with his wife Rosie on board their yacht Wandering Star.

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  1. The primer bulb is helpful when you need to bleed the engine, but they are not approved for below-deck installation. Neither ABYC, the U.S.C.G., nor your insurance company would be very happy with this recommendation.


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So Caribbean you can almost taste the rum...

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