Contact With hot coolant might
result in serious burns.
Do
not bleed
hot,
pressurized coolant
from
a
closed cooling
system.
10.
Slowly open pressure cap and check water level.
11.
Fill system to top with coolant.
WATER
MANIFOLD
FILL
VENT
VALVE
_,
I
t
8378
1
HEAT
EXCHANGER
FIGURE
7.
HEAT
EXCHANGER
FILLING
MARINE
COOLING
SYSTEMS
Three types of marine cooling systems are in general
use today: direct sea water cooling, heat exchanger
cooling, and keel or skin cooling.
Direct sea water cooling systems use an engine
mounted pump to draw flotation water and pump
it
through the engine and out through the exhaust sys-
tem. The floatation or sea water comes in direct con-
tact with the engine water jacket.
INLET FOR
COOLING WATER
FLUSH
i
HULL
The heat exchanger and keel cooling systems were
developed to keep sea water, and the resulting
sediment deposits (salt, silt, etc.), from the engine
cooling jacket. Both systems have a fixed quantity of
captive water in a closed system to cool the engine.
Sea water cools the captive water in the heat
exchanger or keel cooler. Sea water and captive
water are kept separated,
so
the engine water jacket
stays clean. Figure
8
shows a typical marine heat
exchanger.
Because marine generator sets operate typically in
very small compartments,
it
is important that the heat
radiated from the exhaust system be kept to
a
min-
imum.
To
accomplish this, the heated sea water is
usually discharged through the exhaust system.
Special mufflers, pumps, and anti-siphon devices are
required to avoid interference with the passage
of
exhaust gases and to prevent entry of water into the
combustion chamber.
Direct
Cooling
System
Onan engine generator sets constructed for direct
sea water cooling are equipped with a sea water
pump and are normally installed with a water filter,
water inlet valve (sea cock), and strainer.
A
through-the-hull flush-type fitting
is
used for a
water inlet. Heated sea water flows past the thermo-
stat to the exhaust manifold (water cooled) and is
discharged through the exhaust system. The dis-
charged water
cools
the entire exhaust system and
greatly reduces the amount of heat that would
normally radiate from the muffler and exhaust pipe
(see Figure
9).
Although this system is the simplest
and has the lowest initial cost,
it
is not recommended
for salt water or water that contains silt and debris.
WATER TO
EXHAUST LINE
FLEXIBLE
SECTION
LING WATER IN
Y
F
STRAINER
--
PITCH
t
DOWN
TO
MUFFLER
FIGURE
8.
HEAT EXCHANGER
FIGURE
9.
DIRECT SEA WATER COOLING
18
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