This month we are going to talk about fuel systems
and fuel system replacement. Regardless of the car
or truck you are working on, you need to think about
how you are going to address the fuel system. We are
going to talk about replacing tanks only, updating the
line size, cleaning out an existing tank, moving a tank
location, prepping a tank and fuel system for storage,
and trouble shooting gauge problems.
If you are going to change the tank out on your vehicle,
you need to make sure you replace the sending unit at
the same time. This is the biggest mistake that most
people make. You should always try to replace the
tank with an exact replacement tank. If you can't find
one then you will need to repair and clean your old
tank. We will talk about this a little later in the article.
Back to replacing the tank. The major thing is to drain
and properly dispose of the old fuel out of the old tank.
Most cars and trucks had either a 5/16" or 3/8" version
of the sending unit. If you don't know how to tell the
difference by just visually inspecting your old sending
unit, you can always remember that a 5/16" sending
unit will take a 9/16" wrench and a 3/8" will take a 3/8"
wrench. Also, make sure that the sending unit gasket
or o-ring is installed properly and that you don't pinch
or split the gasket or o-ring. If you do this, you will
need to replace it before you install the tank in your car
or truck. The next step is to make sure that your fuel
line is clean of foreign debris. You can do this by
using a blow gun and putting air pressure through the
line. Repeat this process several times to make sure
that the line is clean.
Another major mistake that people make is on the
filler neck. On most trucks the neck is part of the tank
or has only a short neck that attaches by hose and you
can inspect it easily. On a car, the neck is very large
and can't be inspected. I would recommend that you
either sandblast or glass bead the inside of the neck.
This will insure that you do not have any rust or debris
that might make its way into the rest of the fuel system
and lead to clogs.
If you decide to add a big block or a high-performance
small block to your ride, then I would recommend
changing the fuel line at the same time. These
engines need all the fuel they can get. All 6-cylinder
cars/trucks and most small blocks came from the
factory with a 5/16" line. I would recommend that you
change to a 3/8" line. You can buy most lines in a pre-
bent, ready-to-install line. You will need to change the
sending unit at the same time as well.
Now you need to decide on buying a new tank or
cleaning your old one. I would recommend buying a
new tank because you will have more invested in
renewing an old tank, but if no one makes a new tank
then cleaning out the old one is your only option.
There are several companies that offer a "renew"
service where they cut the tank at the seams and
clean and repair the tank.. If you want to try this
yourself, some radiator shops offer to boil a tank out,
or you could use a pressure washer do this. If you use
a pressure washer, you will have to wash it out and
use some form of medium to shake around the inside
of the tank to knock lose any debris and then wash it
out again. You will have to repeat this process several
times.
If you are working on a pre-1972 truck. You need to
think long and hard about moving the fuel tank out of
the cab and putting it under the bed. Not only is this a
safer way of holding the fuel, but you will also no
longer have to smell the fumes from an in-the-cab fuel
tank. If you are working on a car then you don't have to
deal with this problem. We offer a ready-to-install tank
conversion for 1960-66 trucks and for 1967-72 trucks.
These tanks come with a tank, straps, and sending
units. You will have to furnish your own line and wiring
to extend your fuel line and sending unit wiring to the
rear of the truck. This type of conversion can be done
very easily.
Another major mistake people will make is not
prepping a tank or fuel system for storage. Most
people don't drive their ride through the winter
months, so you need to take into consideration that
gas will go bad over time. The best thing you can do is
to drain the fuel system and let the car or truck run
until it's out of gas. If you don't want to take this
measure then you will need to buy a product known as
Stabil Gas Stabilizer. You can purchase this at just
about any parts store, Wal-mart, Kmart, or other
discount chain. This will help you preserve the fuel you
have in your tank over the winter. Also, you need to set
yourself up a schedule to go and start your ride every
week or two. If you store your car or truck where you
can't go and start it every few weeks then, I would
recommend draining the fuel and letting the engine
run until you are out of gas. This will make it a little
difficult to start for the first time in the spring, but it sure
beats having to clean rust and other debris that will
form in the tank over the winter.
The final item we are going to discuss is gauge or
sending unit trouble shooting. If your gauge doesn't
read correctly and you have replaced the sending unit
already, then there are several items you can check
before you start replacing gauges or screaming at
your parts supplier about how the new sending unit
does not work.
First, you will need access to an ohms meter. If you
don't have one, you can pick this item up at your local
auto parts or discount store for a few dollars. Set the
meter according to your instructions then put your red
lead on the wire terminal and the black lead to a good
grounding surface on the sending unit. Then move the
float arm up the full mark and see what the ohms
meter reads. If you are working on a car or truck from
1955 to 1966 your meter should read 28 to 32 ohms. If
the vehicle is 1967 or newer then it should read 85 to
90 ohms.
If your sending unit is within specifications, then you
can check several other things. If you have put some
form of insulation between the tank and bottom of your
car, try taking it out. Using insulation can give you false
ground and will throw the reading off on your dash
gauge. Also, you might try just running a new wire for
the sending unit. This can help you eliminate a wiring
issue. If the sending unit is good and wiring is not
your problem. Your only other choice is to get the
gauge recalibrated, which may not fix your problem.
As always, remember that the ideas we put forth in
this newsletter are only our opinions, but they have
been tried and tested over the past twenty years that
we've been in business.
Next month we are going to talk about carpet types
and installation.
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