Engine Fuel & Fuel Filters

Paul Watson - November 10, 2001

Possibly one of the most common occurrences I have tracked since the days the Seawords was circulated has been the unusual collection of "crud" in the fuel tank. I suppose so many owners were plagued with this malady that any number of filtration devices were often employed and each with a redundant system for longer trips.

My own experience with this problem has caused numerous incidences of the engine suddenly slowing to a stop at precisely the worst time. One, and probably the most fearsome, was on a day I had just sailed, single-handed into Charlotte Amolie, St Thomas, while striking sails under power I had just passed astern of the massive cruise ship docks when "thumper" quit. While too late to raise sails and drifting towards a shallow reef to my leeward side, the Pilot boat accosted me while I was rapidly paying out my anchor. A cruise ship was setting "sail" from the docks and I could easily see the huge churning at its stern, trying to get enough bite to turn itself into the wind. Typically, they had not called for a tug or it was, not surprisingly, late. The aging, thruster-less ship was, no doubt, out of control and rapidly approaching me. I was trying my darnedest to pull up the anchor with hopes of drifting quickly onto the shallows off to my lee before I was to be run down. The Pilot wanted nothing to do with taking me in tow. Five blasts sounded over and over as I pleaded for even a nudge from his fender towards the shallows. Within moments the churning wash from the old cruise ship's propeller shoved me mightily just about the same time his bow inched closer to the wind and he began making way. The distance between our two vessels closed to less than fifty feet before the thankfully, forced separation allowed the return of a normal heart rate.

Needless to say the fuel problem became priority number one, on that day.

The very idea that for near two-dollars per gallon the fuel you put into the tank on your boat contains a very high percentage of emulsified, or suspended, water content seems ridiculous. With such incredibly accurate technology at hand we would expect a well-refined product to be delivered. Well, its not! Refining water completely from diesel fuel is not economically feasible. Beside the trucks and trains and power plants that consume the vast majority of diesel that is refined, boat owners hardly rate as customers to the petro-giants. Most are corporations that own or invest in other companies that make filters. Go figure!

So, we live with certain knowledge that we actually purchase the water that begins the process of making sludge in our tanks. We even perpetuate the problem further by not trying to understand it, let alone prevent it.

First, if the tank we store it in is made of mild or Corten steel, the water, combined with available air, begins the oxidation process that is so easily encouraged in mild steel and a naturally occurring surface sealant for structural Corten. The rust powder insidiously flows from the interior tank walls and settles heavily at the bottom of the inclined tank. The race is on between the accumulating rusty dust to reach the level of the pick-up tube and the tank bottom to deteriorate before the welded seams do.

At first, theory being, the more active boat splashes the protective, oily diesel over the new surface if the boat is delivered to the first owner within hours of actually building the tank.... NOT!

The tanks are most likely produced many months, even years, before they are installed and they are never filled until the boat is launched, possibly two years after the tank was being built. The natural combination of atmospheric condensation and a lack of airflow as well as temperature changes have started rust film only hours after it was completed.

As the rust falls from its original form it leaves behind tiny pores in the surface. These pores continue to grow and provide even more surface area for the expected, suspended water molecules to attach and accelerate the rusting process.

With the arrival of the fuel/suspended water are the microscopic pores of algae that not only survive in the suspension but also actually feed on chemicals found in the petroleum product. Now they begin to multiply in an almost perfect incubator. The older cells die off, leaving behind the cell wall, the husk, which begins to collect among the ferrous oxide molecules, binding them together in a gelatinous goop. I'm sure I need not proceed, you get the picture and certainly you've experienced the result.

Biocide additives are designed to kill off the algae or at least prevent it from immediately proliferating but we always forget to add it or never use it until the problem is out of hand. The only way to get back near to square one is to have the tank purged and the fuel polished to reduce the amount of sludge in the bottom. The process is quite effective it leaves behind about 25% of the original volume of sludge because it agitates the fuel and cannot completely filter the entire suspension. From that point on the oxidation eventually returns to full capacity and soon overcomes the bottom of the tank once again.

As the dimension of the original tank provide space for just about 35-gallons of fuel the space it occupies under the cockpit sole makes removing it quite a chore. But remove it eventually, we must.

From Sharon Cuzner, Silverspray, # 101K,

We replaced ours after 20 years with an alum. one made the same size as the original steel tank. While the steel tank had not leak, we ask the "fuel scrubber" man to pump the tank to get rid of algae and whatever else had settled in it. After inspection he recommended an immediate replacement.
Which we did. Cost was $1,600 done by the yard.

To do so they have to remove the mizzen mast support and cockpit locker fore and aft bulkhead on
the port side. (Of course replacing them after installation). We have been most satisfied and notice remarkably cleaner fuel with very little sediment in the Racor bulb. We have sailed this boat in the Caribbean, Florida, and lots of Northern ports and in 20 + years never encountered a fuel stoppage with the Racor separator. There are also two other in line fuel filters ahead of the Racor that are changed annually.

From Bert de Frondeville, Pianissimo, # 80K,

Dear Paul: We have very similar histories while upgrading for offshore:

1. Fuel Tank(s): Just like you, I felt compelled to replace the aging, scaling Corten steel fuel tank, which was cut into 3 pieces to exit through the port cockpit locker. Loathe to cut the cockpit sole, I chose a new fuel tank made of two identical heavy gauge aluminum tanks extending further aft into the lazarette in order to access the back side where all nipples and lines were located for accessibility, including a dipstick pipe extending to just under the lazarette cover. I have gained precious capacity to 50 gal minus 6% usable

In my own case I ultimately elected to cut out the cockpit sole and replace the mounting platform that had become saturated with fuel and then duplicate the original tank in aluminum. I welded several small "pads" of about 3/16" aluminum to the lower panel to allow air to pass beneath the tank and its mounting board. In the fabrication process I installed a "manhole" in the upper tank panel. The cover panel contains the dipstick access, the fuel return and the pickup tube. It is easily accessed through a Beckson watertight door, beneath the teak grating, for cleaning.

From the point that the tank issue has been dealt with the diligence to provide the engine with clean fuel and a minimum of suspended water becomes a matter for filtration systems that work.

Racor makes a series of very excellent filters and water separators. Unfortunately, often, larger units are selected based upon a presumption that larger capacity that may reduce the amount of filter changes. In all cases, with all manufacturers, the fuel flow-rate is the determining factor for this choice, particularly if a centrifugal water separator is integral. The flow rate for our engines is so slight that separation of the suspension by centrifugal force proves the water separators are quite helpful but not totally efficient.

It is well advised to install a "primary" filter in line before the "secondary" filter. This first unit should trap particulates of about 5 to 10 microns before allowing the fuel into the secondary or "final filter" for further straining down to about 2 microns before sending fuel into the injection pump. On a Westerbeke the final filter is a cartridge type mounted at the very back of the engine and literally impossible to access. It's housing should be removed and re-installed at a more convenient location. ABC Machining, Inc, no address available at this writing, produces a modification of the basic CAV, final filter that converts the original to a spin-on cartridge that can be filled with diesel. The original required laborious bleeding to purge the air from it.

A few contributors indicate that they have installed redundant filtration with valves and some with electric pumps in order to close off one feed circuit, change to an alternative, with the engine running so they may change filters underway. This is typical of most-larger diesel fuel systems in yachts and is just about foolproof.

I still like my dual Racor system in parallel, with ability to inspect, switch at sea and while motoring. that is ahead of the normal fuel filter itself ahead of the engine mechanical filter.

But I shall look into the fuel-water separator... Bert dF


A friend of ours, a world circumnavigator inspected our vessel and suggested that we change our fuel filter system to achieve a filter change at night, no lights, in a minute or so. After some thoughtful and careful movement of the primary filter, installation of a shutoff valve, we have such a system. We have only had to use it on two occasions but one was on a rough rainy night as we were approaching a port downwind with two rock jetties dead ahead. It paid off that night. We changed the filter and had the engine running in only seconds.

2nd thought, when we first obtained our vessel every time we were motoring in rough or rolly conditions the engine fuel filters clogged. At first we thought it was bacteria, but after a few years we came to believe that it was fine rust scale off the walls of the fuel tank. We have a steel tank. To avoid the rust scale, we now keep the tank full of
fuel when at the wharf and this has been a cure for the problem now for over 8 years, now when in rough sea conditions the engine keeps purring.

Don #129

Electric fuel transfer pumps installed in the tank feed line certainly make the occasional bleeding/purging a far more agreeable task.

And so I, once again, come to the end of another essay. With the same hopes that some condensation of our collective wisdom, even if highly editorialized, provides help or even more discussion I close. I'm sure there will be more to come in the future

1440 Jan 30, 2002

Having just relocated my fuel system components to the forward wooden bulkhead on the port side of the engine (backside of the one aft of the kitchen sink), I was wondering if I can attach my water pressure pump to the wooden bulkhead to the port and running perpendicular to that one. It has never been drilled or had anything attached to it before. I want to be certain that I won’t be damaging anything behind it. This would be the wooden section immediately to the left as your looking at the bulkhead behind the sink from the engine compartment. It runs forward of the bridgedeck abutting perpendicular to the sink bulkhead. It is only a foot and a half or so in width.

Any enlightenment would be greatly appreciated.

James, Niko (91)

1441 Jan 30, 2002

I recently changed the way the previous owner had the fuel system set up. Coming from the fuel tank the fuel line goes into a Bug-out magnetic polisher which is hard-connected to a two-way valve which is also hard-connected to a Racor 500 series filter. On the "out" side of the Racor is another two way valve facing downward with a barb fitting. This is connected to an electric priming pump which has a y-valve hard-connected on the output side. One of the valve outputs is connected to the engine’s mechanical pump while the other is connected to a split return fitting at the fuel tank shared with the return line from the engine’s injector pump.

The purpose of all of this? The valves on the fuel filter allow the system to be dismantled while minimizing the mess caused by diesel leakage from the fuel filter. The priming pump which is switched on or off at the breaker panel can be used to allow the engine to self-bleed when prime is lost. The y-valve allows me to recirculate and polish my fuel at dockside where changing filters is a lot more convenient and leisurely (as opposed to doing it when you are in a narrow channel with lots of traffic, winds, or tide).

As I mentioned earlier, all of the components have been mounted on the back side of the bulkhead behind the sink. I was careful to ensure that the fuel filter was easily serviced from this point.

James, Niko (91)

1442 Jan 30, 2002

The bulkhead you refer to is the outside of the icebox. Inside is the insulation for the box. You do not want moisture to get into the insulation. I got moisture into mine and the whole insulation was water soaked and relatively ineffective. I am not sure how thick the bulkhead is, but I think it is ˝" plywood. Any mounting screws should not penetrate through this bulkhead. I have mounted my potable water pump on this bulkhead where it functions without difficulty.

Dick Weaver 75K