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Hands-on advice and instruction.
By Paul Esterle — Spring 2006
Now on to the contamination itself. The first thing you need to understand is that most contamination problems are slow-forming and continuous. For instance, it may take years for enough sludge to build up that it clogs your fuel filters. On the other hand, a single rough trip may be enough to stir up all that crud in your tank's bottom and send it to your suddenly overburdened filters.
A lot of the sludge at the bottom of fuel tanks comes from algae growing at the fuel-water interface. These algae die naturally and sink to the bottom, and they die even faster-and collect in the sludge even faster-if you add a biocide to the tank. What to do? Start by minimizing what they need to grow: water. We've already discussed the most common sources of water, but there's also condensation.
Most condensation occurs on the fuel tank walls, but a little comes from the surface of the fuel itself. Either way, the best way to combat condensation is to keep your tanks topped off. This is especially true during periods of inactivity, such as winterization. The less area is exposed on your tank walls, the less condensation you'll have.
If a contamination problem has already developed inside your tank, fuel polishing may be the answer. Near most marinas, you can find professional fuel polishers who will come to your boat, pump the fuel from your tank, force it through large filters, and put it back in the tank after it's clean. In some cases, the fuel is actually sprayed back into the tank and used to break up any bottom sludge, which then gets filtered out. This part of the process depends on easy access to the top of the tank and suitable access ports (see "How to Add a Fuel-Tank Access Plate," page 91). If your baffles limit access to all parts of your tank, you'll end up paying a professional polisher to clean out some of your fuel, then mix it back in with still-contaminated stuff.
Even if you undergo a successful fuel polishing, your contamination problem may not be solved. The worst-case scenarios may require removal of the tank for proper cleaning. Since many boats have their tanks installed before the deck is placed on the hull, such removals can be extensive, expensive operations.
If that doesn't sound too good to you, but you still have an in-tank problem, you might consider adding chemicals to your fuel. There are hosts of them on the market. Some claim to prevent growth in the tank, while others claim to emulsify the crud, dry the water, and dissolve the contaminants. Note that many diesel engine manufacturers do not recommend these water dryers because they can contain alcohol and therefore cause other problems. Check with your engine distributor first.
FROM TANK TO ENGINE
Your last line of defense is when the fuel is withdrawn from the tank for use in your engine. At minimum, there should be a fuel filter between the engine and the tank, in addition to the filter on the engine. The engine-mounted filter is usually 2 microns, while the first filter is usually 20 or 30 microns.
Regular readers already know my feelings about the importance of having spare filter elements aboard. Also important is knowing how to replace the elements and bleed air from the fuel system. Changing the element almost always introduces some air into the fuel system. You must remove the air or the engine will either not start or quit.
How to bleed your fuel system? The easy answer is: Loosen some connections at specific points, and let the air bubbles escape. The hard part is knowing the location of the bleed points, the sequence required to properly bleed the engine, and the tools you'll need for the job. Waiting until the engine shuts down is not a practice I recommend. If your engine manufacturer or maintenance manuals don't tell you everything you need to know, get a local mechanic to show you the proper technique. An electric priming pump can make this job a lot easier.
Another worthwhile practice is installing dual fuel filters with a valve. This way you can isolate and replace a clogged filter while the engine continues to run on the remaining clean filter. You can assemble a dual-filter unit from an existing single-filter unit and valve or buy a complete dual-filter unit from a manufacturer. Adding a vacuum gauge to either single or duplex filters will warn you that the filter is becoming clogged before the engine starts to miss.
Some boat owners take the process a step further and install an onboard fuel polishing system, which typically includes several filters, an electric fuel pump, and transfer valves. The most complicated setups let you pump fuel to and from any tank while passing the fuel through the filter. The unit can run independently of the fuel supply to the engine, meaning you can clean one tank while running on another tank, keeping not just your engines but everyone aboard happy as well.
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