COOLING SYSTEM
163
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CLOSED COOLING SYSTEM DIAGRAM
Pressure
fill
cap
/
Seawater line
Freshwater line
Freshwater (Closed) Cooling System
Two- and three
-
cylinder engines with a model number
ending in
F
are equipped with seawater and freshwater
(closed) cooling systems
The closed cooling system is divided into two separate
subsystems: one uses seawater and the other uses a cool
-
ant mixture of distilled water and ethylene glycol anti
-
freeze. The subsystem containing the coolant is referred
to as the freshwater system. Refer to the typical freshwa
-
ter cooling system diagram in
Figure
5.
Typical compo
-
nents are shown in
Figure
6.
Various configurations of the closed cooling system are
used, but all function essentially the same. The seawater
system operation is similar to the standard cooling system
previously described, except as follows:
a. Coolant in the closed cooling system cools the en
-
gine block, cylinder head and exhaust manifold.
b. A belt
-
driven seawater pump
(Figure
I),
located at
the front of the engine, delivers seawater to the heat
exchanger, instead of passing seawater directly into
the engine.
After passing through the seawater pump, the seawater
travels through a series of parallel copper tubes in the heat
exchanger, where it absorbs engine heat before returning
to the exhaust elbow for discharge from the boat.
Figure
7
shows a typical heat exchanger.
The freshwater system pump circulates the coolant
mixture inside the engine to absorb engine heat. This
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