This page updated:
Don Casey's "Fuel System Maintenance"
"Feeding the Beast" article (diesel fuel system) by Don Casey
in Nov/Dec 2000 issue of Blue Water Sailing magazine
From McRory's Logbook:
[My boat] is fitted out with two RACOR primary fuel filters plumbed in parallel, with selection
valves. Having them plumbed in parallel means I use one filter at a time. If it gets plugged or
water gets in the system I can switch to a different tank and filter without shutting the engine
off. These are the filters that have the glass bowls and drains on the bottom so you see
what's coming up from your tanks, and sometimes it isn't diesel fuel.
From SG on Cruising World message board:
Get a Racor filter. You can "see" the water.
You can see the color of the fuel (sometimes algae, or worse).
You can add a vacuum gauge and you're done --
you'll change the filter when you need to -- not just to do it.
It might be two years between changes -- or two months, depending on where
you get your tank filled or what you're trying to grow in it.
From Frank Burrows on The Live-Aboard List:
> What pressure range of fuel vacuum gauge should I buy ?
The standard gauge you will find is 0 to 30". My boat runs at 0 with new
filters. I usually change them when they get to 7 or 8 inches. I discovered
that it was reading 15" once but the engine was still going strong. If you
could find a 0 to 20" it might be a little better but these would be hard
to find and I doubt you would see much difference.
Racor has their vacuum gauge color-coded Red for Normal 0-10", Caution
7-10" and Danger 10-15".
From Norm on the IRBS live-aboard mailing list:
Check with Racor for the correct size of Racor. If the Racor is too big for
the flow, it will not have the proper swirl action in the bottom of the unit
to coalesce the water.
From Norm on the IRBS live-aboard mailing list:
... arrange things so that there will never be any water
in the tank, easy to do when
making a new tank. Have the tank builder weld a threaded fitting such as a
pipe coupling cut in half, onto the bottom of the tank, say 1 1/2" onto the
bottom at whichever end will be the lowest after installation. Add a
reduction bushing and draw your fuel from there. Even better, add a 1 1/2"
ball valve, then a longer nipple and a bell reducer. The idea is that any
trash and/or water in the tank goes immediately to the outlet where it can be
dealt with and the tank contains only clean, dry, fuel. If there is some
trash in the tank that plugs the fuel feed line it is a simple matter to
close the ball valve and remove the longer nipple to remove the trash. You
could put a strainer unit between the ball valve and the bell reducer to make
it even more tolerant to trash and more convenient to clean. The more effort
you go through to feed your engine clean, water-free fuel, the less often it
will stop running involuntarily. Lack of a plentiful supply of clean fuel is
the cause of diesel engine stoppage about 90% of the time according to
everything I have read. In my own personal experience it has been 100% of
I use this well setup on Bandersnatch to insure any water in the tank gets
drawn out before any fuel comes out and have never had a problem due to water
in my fuel.
Over the years, as other fuel problems cropped up, I have added more and more
refinements to my fuel system to eliminate each problem. Now the fuel goes
through a coarse (1/4" holes) strainer in the tank, a fine (bronze window
screening) strainer to protect the electric fuel pump (used for priming, fuel
transfer, filling filter housing, polishing fuel, testing for leaks and
flushing air from the system), a fine mesh screen inside the electric fuel
pump, a Racor, and finally the secondary on the engine.
Also be aware, diesel fuel does not like zinc. Galvanize your tank on the
outside only, or just use plain steel then sandblast and do a good paint job
on the outside.
I would also recommend you look at heavily built plastic tanks. They don't
rust, but there is some controversy about their longevity. Be extremely
careful about screwing pipe fittings into plastic tanks, the threaded bosses
are prone to cracking and once damaged are very hard to repair. Use Teflon
tape and do the final tightening with liquid in the tank, tightening only
enough to stop the leaking.
From Norm on the IRBS live-aboard mailing list:
Draw fuel from the absolute lowest point in the tank to minimize the amount
of permanent sludge carried about in the tank. You want the contaminants in
the filters, not in the tank waiting to overwhelm your filters when you have
a MOB situation in heavy weather, drop your sails causing your vessel to
bounce about and stir up the sludge in the fuel tank, and you
really-really-really want your engine to work flawlessly.
A ball valve to shut off the fuel. It would be nice to have valves on
*every* opening of the fuel tank, including fill and vent, to seal in the
fuel in case of a sinking. It will greatly reduce your problems if the boat
An inline screen about the mesh of window screen, easily cleaned. Mine is a
Watts brass fitting, obtainable at a plumbing supply. The original screen
was much too fine so I made my own from bronze window screen. This screen is
just to protect the electric pump and check valve. You really want the
sludge to collect in the Racor. Be aware that Racor has filter elements of
several different micron ratings. I use the smallest I can get. It is much
easier to change one big Racor filter than several smaller secondary filters.
A clear section (I use a 2" piece of clear fuel hose with a spring inside it
to keep it from collapsing) so you can *see* what is being drawn from the
tank like trash or air.
An electric impulse type fuel pump (NAPA, Balknap BK.610-1016, red dot, $108)
to prime, clean, and troubleshoot the fuel system. This type of pump has a
piston and two check valves, just like the old-fashioned well pump, so fuel
can be pulled through it [AKA "flow-through"] by the engine fuel pump. A bypass check valve may
be required depending on required fuel flow rate when the engine is running.
Compound gauges (plus/minus 15psi) on the input and output of the Racor to
see the condition of the filter and another between the secondary (engine
mounted) filter and the injection pump to see the condition of the secondary.
I found some nice ones: Gen Svc Liquid-filled, 304SS case, 1.5" dial, 1/8"
ips bottom fitting, PN 38545K42, $23.64 ea, McMaster-Carr, 404 346-7000,
credit card, UPS.
A crossover valve from the output of the Racor back to the return line to
clean your fuel after taking bunkers.
Another valve to draw fuel from the system at the output of the Racor if you
From Norm on The Live-Aboard List:
> Bought bulbs like the ones on an outboard fuel tank line.
[I also wonder what might happen to the bulb in case of high heat or fire in
the engine compartment. And suppose the bulb flexs constantly as the fuel lift pump sucks
fuel through it; would the bulb crack after a while ? I guess you could install valves
and hose to bypass the bulb when not using it.]
> Put them in each fuel line before the primary filter.
You are fooling yourself. The squeeze bulb is a band-aid, a baby step.
A major problem with the squeeze bulb pump is that minor trash can plug up
the small clearances in the check valves. If you put a filter upstream
between the tank and the bulb to protect the check valves, the bulb will tend
to collapse from the suction of the engine pump and the resistance of the
filter, with said collapse increasing as the filter collects more and more
debris, squeezing the fuel flow down more and more until the engine quits.
From Norm on The Live-Aboard List:
I have read that the fuel microorganisms need water in order to live. If
this is true, then if you keep water out of your fuel tanks, you will not
have a microorganism problem. The key to keeping water out of your fuel
tanks is to draw the fuel from the very bottom of the tank. I have wells
about the size of a cup in the bottom of my tanks and my suction pipes go the
bottom of the wells. By doing this I automatically remove any and all water
every time I withdraw fuel from the tank.
Putting the ends of the suction tubes an inch or two above the bottom is a
technique left over from the days of professional engineers and day tanks on
yachts where the engineer would drain the day tank from a valve on its very
bottom to be sure there was no water in it every time he filled it up.
Unless you have such a drain valve on your fuel tank, or use the well or
similar technique as I do, you *will* accumulate water and associated
microorganism glop in your tanks.
A fuel preservative would be a good idea for fuel stored for months at a
time, but that is only to protect already clean fuel. You really must keep
the water from accumulating in the bottom of your tank.
From article by Steve D'Antonio in 11/2002 issue of Cruising World magazine:
- Need inspection/cleanout port into every baffled chamber.
- Inspection port should be same material as tank.
Port cover plates should be thicker than tank wall, to avoid
distortion and bad seal.
- If adding an inspection port to an existing tank, could use
a specialized rivet with internal threads to provide seat for
the bolts. Or use a split inside ring from Clarus.
- Don't want a drain valve in the bottom of the tank.
- Don't want a screen in the pickup tube inside the tank;
if it clogs, there's no easy way to detect it or clean it.
- Use a fuel-proof thread sealant, such as Jomar Seal or Argco LeakLock.
Teflon tape should not be used.
From Cruising World's "Find It, Fix It, Maintain It":
When possible, buy your diesel from automotive pumps
rather than fuel docks. The turnover is higher, so the fuel
is generally much cleaner and it is well worth the trouble
of getting it to your boat.
From Jerry Nessenson on Sail World 6/2011:
Ultra low sulfur diesel fuel, now required by the EPA to be sold by virtually all marinas,
contains less than 15 parts per million (a 90% reduction) of sulfur and is better for the environment.
However, it can cause a multitude of fuel-related problems and requires more than just a biocide that only prevents bacteria.
Ultra low sulfur diesel fuel quickly becomes unstable and contains a high moisture content that leads to corrosion,
sludge and plugged fuel filters. More importantly, the sulfur in high sulfur diesel fuel lubricated the fuel injectors
and fuel pump. The lack of lubrication can cause expensive premature failure of injectors and fuel pumps unless
the ultra low sulfur diesel is treated with a lubricity improver.
From interview of Richard Steinke in Latitude 38:
Mount an electric fuel pump as a backup to the manual transfer pump.
It makes priming after a filter change easier, and in an emergency
will overcome the effect of a small air leak.
It also makes it easier to spot air leaks.
From captkeywest on the Cruising World message board:
... install a vacuum gauge [between primary filter and lift pump] so you can
monitor your filter's progressive restriction, avoid
unnecessary changes, and most importantly avoid untimely
engine shut downs due to a clogged filter. ...
From KC on the Morgan mailing list:
Use the stick method. Pump all the fuel
out of the tank that you can thru the normal pickup. You can use a 12 vdc
pump from Napa and it will do the trick easy. After you have the tank empty,
add fuel a gallon at a time. Either by jug or watch the pump at the dock. and
mark the stick as you add fuel. Please do not do this on a Saturday morning.
The guy behind you will have a fit as it will take a little time.
Then take the stick and transfer the marking to somewhere on the wall in the
engine room. If you or the next owner lose the stick the calibration is
Now for fuel care. Use that little pump inline with your current system, but
leave the pump off. The right pump is one that you can blow thru if it is
Now for the good part. If you have a fuel starvation problem due to
whatever, you can turn this pump on and it will draw more fuel thru a clogged
filter for a short time. Just what you need sometimes.
From Larry Zeitlinon Great-loop mailing list:
A leaking or broken injector pipe is fairly common. The pipes are subject to
high pressure and vibration and any flaw is soon revealed. It is rare that the
tubing actually breaks. The usual leakage site is at the joints or
compression fittings, probably due to repeated overtightening. If your injector pipe
leaked two gallons into the bilge it must have been leaking for several hours.
If you discover a leaking pipe during the middle of the passage, DON'T CRIMP
THE PIPE SHUT. This will ruin the expensive injector pump. Rather disconnect
the end from the injector, slip a plastic tube over it, and direct the open end
into a 2-liter soda bottle. Check the bottle every hour and empty it back
into the fuel tank. Then limp home on the remaining cylinders.
From Gene Gruender on The Live-Aboard List:
Re: fuel tank gauge:
Others mentioned the sending units from West Marine. I put one in my
tank and the thing I learned is that the manufacturer can't
measure tank sizes. They list them as for a certain tank depth,
but if you get one, you need one for a tank several inches deeper
than what will be listed on the package. I had to take mine back
and get the next deeper size, and it still isn't deep enough. I
would have gotten the one 2 sizes deeper than the actual tank
depth except I had to bend the arm on the second one to get it
located before I realized that, even though it was listed as for a
tank 3" deeper than mine, it still didn't reach the bottom. Now,
when it's about 3/4 full, mine says empty.
Bottom line, don't pay any attention to the sizes mentioned on the
package, measure the unit yourself and make sure it will drop down
as much as you need.
Fuel senders from wemausa; vertical float instead of one on an arm.
Also a model that incorporates an extra fuel draw and return for use with a polishing system.
Filter pore size:
I was surprised to find that the finest fuel filter in my system had 10-micron pores;
many people use much finer filters, down to 2-micron pores. But you can't just
change from 10 to 2 blithely; you have to be able to get enough fuel flow through
the filter, and avoid applying too much suction/vacuum to the fuel pump.
Chris Woodbury's "Nauticat-Fitted Fuel Polishing Systems"
- Want stop-cocks on both sides of primary fuel
filter to keep air out of fuel lines while changing filter.
- When bleeding air out of fuel line, catch any vented fuel.
Diesel will soften/destroy wire insulation
and rubber engine mounts.
- When bleeding air out of fuel line, if manual pumping
of fuel lift pump isn't working, try brief shot of starting motor to
move cam to different position.
- Use an outboard motor priming bulb (before lift pump) as a cheap pump
for bleeding air out of fuel line.
Mount it high so if there was a problem with the bulb itself (leak),
the leak would act as a siphon break and prevent contents
of fuel tank from siphoning to bilge.
- When singlehanding, need a way to crank the engine
while bleeding the fuel lines.
- From Ed / Thumper on the Cruising World message board:
"If you crank the engine to bleed, be sure to close
the raw water seacock; extended cranking can cause water
to back up into the cylinders."
- When fueling, use a fuel filter such as
(recommended; cheap; get Heavy Duty Inspection Filter model)
or "Baja filter" (expensive).
$29 West Marine WM-F8C rated better than Baja Filter ($130)
by Practical Sailor.
But they slow fueling, and are bulky and smelly to store.
Need to be metal, to preserve grounding (especially if using gasoline).
After filling, remove the screens and wipe
leftover fuel out of screens and inside of cylinder.
- Have some simple way to polish fuel yourself.
Maybe a hand pump or electric pump,
hose into filler neck and to bottom of fuel tank,
inline filter, and hose back into fuel tank.
- From AutoSite:
"Water separators ... should be mounted upstream of the fuel
pump because they're not as efficient at removing water from
an emulsion ..."
(so order is tank, separator, pump, engine)
- Some tanks have a filter inside the fuel pick-up tube.
Remove it completely; if it gunks up, there's no way to get to it.
- Some lift pumps contain a small filter.
- Don't use any fuel additive that contains alcohol (it damages seals).
- Racor filter housing has a check-valve that can get gunked up.
- A cruising sailboat should have a water
separator that is bigger than "recommended",
because worse than usual fuel will be encountered.
- Making fiberglass tanks: to prevent leaks: lay up the tank,
let it dry, grind inner surface, add more layers on inside.
- Use a hand pump with a rigid hose to get crud out
of the bottom of the fuel tank.
- Carry 5 gallons of spare diesel in a jug, in case the fuel
tank gets contaminated, leaks, or fuel line breaks.
- If running your engine out of a fuel jug, because of tank problems,
run the fuel return line back into the jug. Some engines return 90% of the fuel
they draw in.
- If running out of diesel, stretch it with oil plus gasoline.
- Fuel tank vent should be as high as possible, protected from water,
and not in an area where water can pool.
- Fresh diesel has a strong smell; old diesel will have lost most of its smell.
- If you need to have bad fuel pumped out of a tank, call
a fuel-polishing service or an oil-recycling company. Apparently disposing of dirty diesel
isn't too bad; disposing of dirty gasoline is expensive.
- Apparently what grows in water in old diesel fuel is bacteria, not algae.
- Some people say adding Bio-Bor to a diesel tank just creates tons of crud and clogs your
filters. The real story seems to be: if your fuel is in good shape, adding Bio-Bor routinely
is a good thing to do. If instead you have let your fuel become very dirty, the first application of Bio-Bor will
lead to horrendous clogging. Once you get the fuel clean, routine use of Bio-Bor will help keep it clean.
- Changing to Bio-Diesel: it will emulsify anything growing in your fuel tank,
leading to lots of filter clogs until the tank gets cleaned up.
Algae-x Magnetic Fuel Conditioning (some people think this is nonsense)
De-Bug Fuel Decontamination Unit (some people think this is nonsense)
Wil Andrews' "Captn Wil's Diesel Polishing System"
Fuel tank article by Nick Bailey in issue 2000 #1 of DIY Boat Owner magazine
Fuel/water/waste tank articles in Oct 2000 issue of Cruising World magazine
Fuel system article by Steve D'Antonio in July 2001 issue of Cruising World magazine
New to Diesel Engines ?
Jesse Brett's "Fuel Systems Explained"
From RichH on Cruising World message board:
A recirculation polishing system takes advantage of 'turnover' flowrate and a filter that is much coarser than
the prefilters found in a normal "in-line" filter set. A coarse filter will have little resistance to flow (GPM/psid)
and yet have retention ability down to the sub-micron levels ... but not a very high efficiency of capture.
So using a coarse filter with for example a 12v fuel transfer pump (3 gallons per minute @ 1psid)
will allow you to 'turn over' the tank volume many times. Each time through, more and more of the very
small particulates become trapped until you haave essentially a total background of only submicronic particulate.
Coarse filters are cheaper than 'fine' filters. A prime benefit of a high turnover recirculation system is its 'recovery' --- if a
huge amount of particulate comes loose from the tank walls, the particle load will 'recover' back to normal due
to the high turnover rate --- With a lift pump (at about 2 gallons per HOUR capacity in comparison to a transfer pump
at 3 gallons per MINUTE (180 gallons per HOUR) ... the transfer pumps system will turn-over almost
100 times as much fuel in the same time!
I'd disagree with the use of a Racor; they are relatively expensive (huge mark-up for the distributor/reseller) and are more or less
designed for 'single pass' filtration. For the filter I'd recommmend a 2.5" diameter by 10 inch
long, spun bonded polypropylene
microfiber media 15-20 �M about $8 in a cheapo carbon steel 'oil-burner' filter ($60).
Since such transfer pumps usually come with
a protective suction screen, I'd pressure-feed the filter with the transfer pump for
the longest in-service life of that filter
(vacuum-feed filters are VERY inefficient with respect to 'on-stream or 'service life').
A Walbro model 6802 12v 3 gpm transfer pump is about $150.
From Ed Kelly on The Live-Aboard List:
Re: Epoxy tank coating:
Go very slowly in building Epoxy tanks intended for gasoline.
The formulations of fuels have been changing. What you build for gas
in a few years may have other additives in it. By law and in pursuit of
profit, fuel is expected to contain more and more Ethanol and other
alcohols in the future. Some are destructive of Epoxy. I understand
there have been more and more problems of late with tanks failing due
to other solvents in the gasoline.
... We earlier talked to the West system epoxy experts and they
advised of the problems with some gas formulations ...
Biodiesel and alternative fuels:
Article by Durkee Richards in July/August 2005 issue of Good Old Boat magazine
SoyGold's BioDiesel page
Bob Senter article on SailWorld
- Petro-diesel (normal diesel). There are several grades of this; typical is diesel #2.
- Low-sulphur petro-diesel. Emits fewer pollutants, but has less lubricity than
normal petro-diesel, so may cause more engine wear.
- Bio-diesel (pure bio-diesel). Manufactured from vegetable oils, greases, or animal fats.
- Bio-/petro-diesel blends. For example, B20 is 20% bio-diesel and 80% petro-diesel #2.
- Vegetable oil. Can be burned directly if heated to reduce viscosity, and if engine
is started on some other fuel first.
Advantages of bio-diesel and bio-/petro-diesel blends:
- Bio-diesel has increased lubricity compared to petro-diesel, so less
wear on engine parts (even a B5 blend is enough to get this effect).
- Bio-diesel produces less pollutants than petro-diesel when burned,
and the exhaust smells better.
- Bio-diesel is more biodegradable, so spills are less harmful to the environment.
- Bio-diesel is a renewable fuel (but some fossil fuels are used to produce bio-diesel,
so it's not completely renewable).
- Bio-diesel is safer to handle than petro-diesel: bio-diesel has a lower
flash-point, and is non-toxic to humans.
- Bio-diesel may improve fuel stability in the tank, at least in blends such as B20.
- Bio-diesel may allow longer oil-change intervals, because of cleaner combustion.
Disadvantages of bio-diesel:
- Higher cost than petro-diesel (even with tax breaks).
- Lower energy content than petro-diesel; less
power and mileage per gallon.
- Higher solvency than petro-diesel. Old deposits on fuel tank walls may get
loosened and clog filters. Rubber fuel lines and gaskets may swell and weaken.
Spills can damage paint and polysulfide caulk.
- Lower flash-point means harder to start engine in cold weather, and
- Status of new engine warranty when using bio-diesel may be unclear.
- Fuel stability in the tank for pure bio-diesel is not clear, especially
because of biodegradability and microbial growth.
From Nigel Calder in 2/2008 issue of Sail magazine:
Re: Ethanol in gasoline:
Ethanol, a solvent, will dissolve accumulated dirt in older fuel systems, often
resulting in plugged filters and fuel lines. It can also
dissolve the resin used in making vertian fiberglass fuel tanks.
[It will absorb moisture from the atmosphere, and at saturation point,
the waterlogged ethanol will settle to the bottom of the tank and
make the engine operate erratically or even stop.]
... install an ethanol-compatible 10-micron water-separating filter. [Expect to have
to clean it regularly for a while.] ...
From page on Sail World
... Yanmar Marine warns boat builders and other customers that biodiesel blends
can adversely affect certain metal, rubber and plastic components of engine fuel supply and return systems.
Biodiesel-compatible components must be used instead, so that deterioration and damage
do not occur. Builders and/or customers must verify that they are using the correct
fuel supply and return system materials, otherwise they will lose their engine warranty protection. ...
From BoatUS article on Sail World about E-15 gasoline:
"... the widely known problems with ethanol's ability to attract water into gasoline,
degrade fiberglass gas tank walls to the point of failure, and its solvent-like quality
which has led to catastrophic boat engine failures and major repair or replacement costs."
From Glen Tuttle on Sail World
Lauren Dunn's "US Body issues damning verdict on E15" on Sail World
When we removed the inspection port on the suspect tank, both [2-year-old]
Buna-N gaskets were totally disintegrated, and chunks of them had stopped up the fuel ports.
We checked on the other tank and same thing happened, but to a lesser degree as those
gaskets were only about a year old.
An hour of Internet research revealed:
All known gaskets, seals, hoses and O-rings are compatible with blends of less than 20% biodiesel.
For higher BioheatR fuel Blends than 20% biodiesel, up to and including 100% biodiesel,
compatibility will depend on the materials they are made from. For BioheatR fuel Blend
concentrations over 20% biodiesel, fluorinated polyethylene, fluorinated polypropylene,
Teflon, Teflon lined, or Viton Components are recommended. Use of other types of materials
in BioheatR fuel Blends over 20% biodiesel such as nitrile, natural rubber, or Buna-N type
rubbers may cause leaks, plugged filters (due to dissolved material) and eventually
complete gasket, seal, hose or O-ring failure.
From George Adams on MadSci:
Re: Can gasoline be used in a diesel engine ?
Gasoline in a diesel engine: I think mistimed ignition
could break piston connecting rods or damage crankshaft bearings and destroy the engine. And gasoline
lubricates less than diesel fuel, so you might wear down cylinder walls or the fuel injection pump.
And alcohol in gasoline might affect fuel system gaskets and hoses.
And unburnt gasoline could ignite inside the exhaust system.
But I do know someone who mixed about 4% oil into gasoline and ran a diesel
engine on it for several hours to get into port.
Gasoline and diesel fuel are very similar. Gasoline is the portion of
crude oil that boils between about 100 and 400 degrees F. Diesel fuel is
the portion of crude oil that boils between about 400 and 600 degrees F.
However, an ordinary diesel engine will not run on gasoline, and a gasoline
engine will not run on diesel fuel.
A gasoline engine works by compressing a mixture of gasoline vapors
and air in a cylinder and igniting it with a spark, driving the piston and
creating the power. A diesel engine works by compressing air in a
cylinder and injecting a liquid fuel into the cylinder. The air must be
compressed to a high enough pressure (much higher than a gasoline engine's
pressure) that it will be hot enough to ignite the fuel without a spark.
If you try to run a gasoline engine on diesel fuel, the fuel will not be
vaporized satisfactorily, and if it ran at all it would be sluggish and
would exhaust a cloud of smoke. If you try to run a diesel engine on
gasoline, the gasoline will vaporize and ignite prematurely and the engine
will sputter and knock and eventually stall. (I know this from experience
because I once rented a car that I did not know had a diesel engine and I
filled the tank with gasoline.)
Kerosene and jet fuel are portions of crude oil that are similar to diesel
except that they usually will not contain the highest boiling part. They
should work in a diesel engine, but not in a gasoline engine.
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