3Com Caterpillar Commercial Diesel Engine SEBU6251-06 - Manual (Page 23)

23
Maintenance Section
Fuel Specifications
5. Determine the lowest outside temperature
for machine operation. Find this point on the
left side of the table. Mark this point. Draw a
horizontal line from this point. Stop the line at the
intersection of line “A”. Label this new line “C”.
6. Line “C” and line “A” intersect. Mark this point.
Draw a vertical line from this point. Stop the
line at the bottom of the table. Label this line
“B”. The point at the bottom of line “B” reveals
the percentage of lighter fuel that is required to
modify the pour point.
The above example shows that the blending will
require a thirty percent mixture of lighter fuel.
Additives are a good method to use in order to
lower the pour point of a fuel. These additives are
known by the following names: pour depressants,
cold flow improvers, and wax modifiers. When the
additives are used in a low concentration, the fuel
will flow through pumps, lines, and hoses. These
additives must be thoroughly mixed into the fuel at
temperatures that are above the cloud point. The
fuel supplier should be contacted in order to blend
the fuel with the additives. The blended fuel can be
delivered to your fuel tanks.
Moisture Content
Problems with fuel filters can occur at any time. The
cause of the problem can be water in the fuel or
moisture in the fuel. At low temperatures, moisture
causes special problems. There are three types of
moisture in fuel: dissolved moisture (moisture in
solution), free and dispersed moisture in the fuel,
and free and settled at the bottom of the tank.
Most diesel fuels have some dissolved moisture.
Just as the moisture in air, the fuel can only contain
a specific maximum amount of moisture at any one
temperature. The amount becomes less as the
temperature is lowered. For example, a fuel could
contain 100 ppm (0.010 percent) of water in solution
at 18

C (65

F). This same fuel can possibly hold
only 30 ppm (0.003 percent) at 4

C (40

F).
After the fuel has absorbed the maximum possible
amount of water, the additional water will be free
and dispersed. Free and dispersed moisture is
fine droplets of water that is suspended in the fuel.
Since the water is heavier than the fuel, the water
will slowly become free and settled at the bottom
of the tank. In the above example, when the fuel
temperature was lowered from 18

C (65

F) to 4

C
(40

F), 70 ppm of water became free and dispersed
in the fuel.
The small drops of water cause a cloudy
appearance in the fuel. If the change in temperature
is slow, the small drops of water can settle to the
bottom of the tank. When the fuel temperature
is lowered rapidly to freezing temperature, the
moisture that comes out-of-solution changes to very
fine particles of ice instead of small drops of water.
The particles of ice are lighter than the fuel, and
the particles of ice will not settle to the bottom of
the tank. When this type of moisture is mixed in
the fuel, this moisture will fill the fuel filters. The ice
crystals will plug the fuel filters in the same way as
wax plugs the fuel filters.
If a filter is plugged and fuel flow is stopped,
perform the following procedure to determine the
cause:
1. Remove the fuel filters.
2. Cut the fuel filters open.
3. Inspect the fuel filter before the filter warms. This
inspection will show that the filter is filled with
particles of either ice or wax.
The moisture which is free and settled at the bottom
of the tank can become mixed with the fuel. The
force of any pumping action will mix the moisture
with the fuel whenever fuel is transferred. This
moisture then becomes free and dispersed water.
This moisture can cause ice in the filters. This
moisture can cause other problems with filters at
any temperature. Generally, the same force that
mixes the water into the fuel will also mix dirt and
rust from the bottom of the tank with the water. The
result is a dirty mixture of fuel and water which can
also fill the filters and stop fuel flow.