Exhaust
System
'
Unitsof
Measurement
Inches
of
Water
Inches
of
Mercury
Ounces
GENERAL
The exhaust system must efficiently expel all engine
combustion products and muff
le
exhaust noises with
minimum back pressure. If back pressure is too high,
volumetric efficiency of the engine is reduced, fuel
economy drops, exhaust temperature increases, and
valve life is shortened.
Full
Load
27
2
15.6
02.
Back pressure must not exceed
27
inches
(686
mm)
of water column for the rated load when measured
with a manometer at the exhaust manifold, Figure
3.
FIGURE
3.
BACK
PRESSURE TEST WITH MANOMETER
EXHAUST SMOKE
A
light gray or light bluesmoke may bearesultof low
ambient temperature and light load. This smoke is
unburned fuel (not harmful to the engine) and disap-
pears when more load is applied.
Black smoke indicates overfueling (more fuel than
oxygen) and is usually caused by overloading. The
smoke or unburned fuel becomes carbon when
raised to a high temperature. Carbon contributes to
engine damage because it contaminates the iubricat-
ing
oil.
Inhalation of exhaust gases might
a
result
in
serious personal injury or
death.
Do
not use exhaust heat
to
warm a room,
compartment,
or
storage area.
WARNING
Vent exhaust gases outside. Use flexible tubing only
between the engine exhaust outlet and rigid piping.
Inhalation
of
exhausf gases might
result in serious personal injury or
death. Inspect exhaust system audibly and visually
for leaks dally. Repair any leaks immediately.
WATER
COOLED
EXHAUST
Marine exhaust systems are designed
so
that a
minimum mount of heat will be radiated from the
exhaust system components. This is done
to
keep the
heat b'uild-up
in
the engine compartment to a min-
imum. Exhaust heat is dissipated by using a water
cooled exhaust manifold and a water injected exhaust
pipe and muffler system. The exhaust manifold is
encased ina shell through which engine coolant or
sea water is circulated. Just beyond the exhaust
manifold,
a
special elbow (see Figure
4)
is fitted
which allows the output water from the sea water
system to be injected into the exhaust pipe. The
injected sea water is carried out thorugh the exhaust
system and discharged into
the
flotation water.
CONNECTED
TO
EXHAUST
MANIFOLD
.\
SEA
WATER
INPUT
EXHAUST
ELBOW
ASSEMBLY
APPLY
PIPE
TO
ALL
PIPE
TWO
HOSE
CLAMPS
HIGH
EXHAUST
TEMPERATURE
RUBBER
EXHAUST
SHUTDOWN
SWITCH
HOSE
EXS-1014
FIGURE
4.
EXHAUST ELBOW
14
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