METAL BODY REPAIR - OD1653 - LESSON 2/TASK 3
air of no more than five psi, and look for air bubbles.
Mark these spots
(3) Another method is to fill the tank with clean water, soap the
outside of the tank, replace the tank cap, and attach an air line to the
fuel outlet connection.
Apply five psi of air pressure and look for any
bubbles which may appear on the outside of the tank which indicates a leak.
(4) Testing for leaks in the fiberglass and cell (bladder) type of fuel
tank is more or less a matter of visual inspection. In cell (bladder) type
fuel tanks, leaks may occur because of punctures, cuts, abrasions, blisters,
and ruptures. Scuffs and coating damage may also cause occasional leaks.
e. Cleaning. Before repairs, fuel tanks must be cleaned thoroughly. This
is absolutely necessary as a safety precaution-against fuel or vapors
remaining in the tank. Never be misled by the fact that the tank is empty
of liquid. There may be vapors in a tank that has been empty several weeks
or months. When heat is applied to the tank, the metal expands and any fuel
that may have been trapped in the seams vaporizes and explodes.
(1) The best method of cleaning a fuel tank is the live steam method.
This consists of using a steam cleaner to remove any fuel or fumes that may
still be present. After flushing the tank with water, remove all tank units
and fittings such as the drain plug, fuel pickup assembly, gas gage, and
filler cap. Place the steam cleaner hose in the filler neck and steam the
inside of the tank for at least 45 minutes with live steam. Repairs should
be done immediately after cleaning.
(2) The exhaust-and-air method does not require anything more than a
vehicle that runs and a 1 1/2 inch flexible pipe. Remove the tank from the
vehicle. Place the 1 1/2 inch flexible hose into the gas tank filler neck.
Connect the other end to another vehicle exhaust pipe. Let the vehicle run
for at least 25 minutes. After the exhaust fumes have been running into the
fuel tank for at least 25 minutes, blow the tank out with compressed air and
start repairs immediately. By starting repairs immediately, vapors have not
had a chance to build up again.