FUEL FILTRATION: Part II
written by: Harry Lewellyn
This article is a reprint from the Bonus Issue of FOURWHEELING ACADEMY.
The FOURWHEELING ACADEMY is a regular part of
the "Ecological 4Wheeling Adventures" Newsletter.
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On my Copper Canyon expedition, I require that all
participants carry a spare fuel filter and the necessary "change" tools. Originally, I
thought we took on lots of dirty, backcountry gasoline, but have since learned that's not the
case. It's the long dusty environment and other things that cause fuel filter problems.
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RUSTY TANK INTERIOR
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Aftermarket tanks are not perfect. I had an increased-capacity tank that clogged fuel filters. A fine iron
oxide formed inside the tank and clogged filter after filter. The filter was doing a perfect job, but the tank was creating lots of rust.
I surmise, disregarding the psychoanalytical implications,
you can look at the tank as averaging half empty all the time. At empty, half the upper portion of
the tank is constantly exposed to moist, oxygen-laden air. This rusted the tank. The continually
sloshing gasoline "scrubbed" the rust off the tank walls and made it easier to re-rust
— fast! The gasoline recirculated, the rust was continually "cleaned" from the
system and it eventually clogged the filter.
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With onboard instrumentation, I
could monitor fuel flow (gallons per hour or GPH). Under heavy load, when clogged, the GPH was not
up to snuff. I hack sawed open a filter or two to discover a fine red powder that I eventually
traced to the rusty tank interior. To ease field problems, I installed a pre-filter. When the GPH
dropped below an acceptable level, I'd simply bypass the first filter via a valve and use only
the second one. Then, at home, I'd replace the pre-filter. This was some years back and I
suspect new gas tank material regulations have made this a little better. However, the principle
still applies to even the "better" tanks.
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LEAKY VENTS
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On another occasion, a Copper
Canyon traveler's aftermarket tank had a faulty vent. The vent sucked dirt. The recirculating
fuel system continually removed the dirt. This clogged the filter surprisingly fast. My stock
Explorer tank had a similar problem. The vent hose would pop out of the force-fit grommet and suck
dirt. Recirculating systems are great, but look out. If dirt is continually introduced, the system
may clog the filter in less than a day!
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FILTER DESIGNS
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Filters take on two designs:
depth filters and surface filters. Depth filters try to trap the contaminants in the filter. This
is old technology and only stops about 95%¹ of injurious contaminants. Old-fashioned oil bath
air filters were of this design. Surface filters stop the bad stuff at the surface. They are
99.9%² effective for all contaminants. They will stop a particle as small as 10 to 20
microns³ (one micron is 0.000039 inch).
To further scope in a micron, a human hair is 60-70 microns,
talcum powder is 10 microns, airborne dust may be as fine as 1-3 micron and tobacco smoke is 0.5
microns. The human eye cannot distinguish particles much below 40 microns&sup4;.
Modern gasoline fuel filters are pleated, surface, paper
filters.
...... continued on NEXT PAGE ..
Look for a future article on air filters. There's more to it
than simply volumetric flow! Cleanliness is my first priority.
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Author's Note
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This article first appeared in the November-December 2001
issue of Ecological 4Wheeling Adventures newsletter.
Vent fittings of the screw-in variety all but eliminate loose fitting contamination
entry, period. Add steel shields beneath stainless steel tanks with screw-in fittings and
you've got the best combination of contamination-free, bullet-proof, off
highway fuel container possible!
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FUEL FILTRATION : : [ PAGE 2 ] : :
[ PAGE 3 ]
STILL CONFUSED? CHECK OUT [ EFI 101 ]
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About the Author
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Harry Lewellyn is the author of "SHIFTING into 4WD" and the
"California OHV Guidebook" produced by the state of California Department of Parks and Recreation.
He leads 4WD trips throughout the US, Baja and mainland Mexico.
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