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Hands-on advice and instruction.
By Paul Esterle — Spring 2006
Finding and Fixing
Flexible Impeller Pumps
Your average diesel needs three basic things: clean air, clean lube oil, and clean fuel. Dusty air is rarely a major problem aboard a boat, and having clean lube oil is a simple matter of maintenance, such as regular filter and oil changes. That leaves the issue of feeding your engine clean fuel.
Some engine experts suggest that 80 to 90 percent of diesel engine problems are the result of dirty or contaminated fuel. There are two common kinds of fuel contamination. The first is water in the fuel, which makes diesel injectors and injector pumps very unhappy. In addition to being harmful to these precision components, water harbors the growth of algae along the water-diesel interface. These organisms die and then contribute to the sludge buildup in diesel tanks.
The second form of fouled fuel involves solid contaminants. Dirt and rust flakes from stowage tanks are usually present in your fuel, often in far greater quantities than you might imagine. There also is anecdotal evidence that some contaminants (called asphaltenes) form from the refined fuel itself, discoloring the fuel and adding to the con-taminate mix.
Whether you think you've got a water- or solid-contamination problem in your- fuel, a good strategy for fixing it should cover three areas: how the fuel goes into the tank, what happens inside the tank, and how the fuel moves from the tank into your engine.
The best part of this simple design is that the fluids
actually lubricate the pumps during the process.
GOING INTO THE TANK
Your first line of defense against dirty fuel occurs during fueling. Many people say that buying fuel from high-volume dealers is the best way to go, and I agree that doing so is a decent strategy, since it minimizes problems with condensation and settling that occur when fuel is allowed to sit.
However, even high-volume dealers can have problems with water and particulate contamination leaking into their tanks. The problem gets worse when you refuel from lower-volume dealers or from 55-gallon drums that have been sitting around for who knows how long.
Unfortunately, cruising often involves filling up during bad weather or under other uncontrollable circumstances, so it's a smart move to buy one of the several filters on the market that fit into the fuel fill port, preventing dirt and water from getting in. I believe the Baja filter is the most effective, but there are several less-expensive options that work pretty well, too. (If you think your fuel source is safe, test it by pouring some fuel into a clean glass container and letting it settle. Water will drop to the bottom, and any solids will be clearly visible. You may just end up buying that filter after all.)
Keep in mind, though, that there are a couple of downsides to using such external filters. First, they slow down the fuel flow, meaning it will take longer to fill your tanks. Second, you'll need to clean the filter after every use; a messy process. There is also the matter of price. These filters go for anywhere from $260 for the large Baja filter down to $65 for the well-respected West Marine WM-F8C.
Remember that not all contamination comes from the fuel dock. One of the most common sources for water in a diesel tanks is a missing or leaking O-ring. If in doubt, replace it. It's cheap insurance.
IN THE TANK
Now let's deal with the design of the tank itself. A proper diesel tank should have all connections coming in from its top. The fill tube should extend well into the tank to minimize fuel foaming during refueling, and there should be baffles inside to prevent the fuel from sloshing back and forth-and stirring up the sludge that clogs your filters. Ideally, there should be a sump or depressed area in the bottom of the tank to collect sludge so it can be periodically cleaned out. Also, the fuel pickup line should stop several inches above the bottom of the tank to keep it above any sludge buildup. (If the sludge reaches your pickup, it's time for a serious tank cleanout.) Finally, there should be enough access plates in your tank to let you clean out each baffled section.
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