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SECTION R
COOLING SYSTEM (EXTERNAL)
1. DESCRIPTION:
Wes~erbeke.marine
diesel engines are
equlpped wlth fresh water cooling.
Transfer of heat from engine fresh
water to sea water is accomo1ished
in a heat exchanger, similar in func-
tion to an automotive radiator. Sea
water flows through the tubes of the
heat exchanger while fresh water
flows around the tubes. The sea
water and fresh water never mix
with the result that the cooling
water passages in the engine stay
clean.
2.
FRESH WATER CIRCUIT:
Heat rejected during combustion, as
~ell
as heat developed by friction,
lS absorbed by the fresh water whose
flow is created by a fresh water cir-
culating pump. The fresh water flows
from the engine through a fresh water
cooled exhaust manifold, a heat ex-
changer, in most cases an oil cooler
and returns to the suction side of '
the fresh water circulating pump.
The flow is not necessarily in this
order in every model. When starting
a cold engine, most of the external
flow to the heat exchanger is pre-
vented by the closed thermostat.
Some amount of by-pass is maintained
to
~revent
overheating in the exhaust
manlfold. As the engine warms up the
thermostat begins to open up a11~wing
full flow of engine fresh water thru
the external cooling system.
3.
SEA WATER CIRCUIT:
The.s~a wa~er
flow is created by a
posltlVe dlsp1acement neoprene inpe11e--
pump (gear pump in certain special
cases).
Normally the pump draws sea
water directly from the ocean via the
sea cock and sea water strainer. Some-
times a transmission oil cooler, or
pehaps a V drive will be piped on the
suction side of the sea water pump.
Gen~rally
it is better to have as few
devlces on the suction side of the sea
wa~e~ pum~ a~
possible to preclude
prlmlng dlfflculties.
Usually sea
water flows directly from the dis-
charge of the sea water pump to the
heat exchanger sea water inlet. After
passing through the tubes of the heat
exchanger, the sea water may enter a
transmission oil cooler if present
and if sea water cooled. Ultimately,
the sea water enters a water injected,
wet exhaust system, the most popular
type of exhaust system in use. In
the case of larger engines the sea
~ater
flow is divided prior to enter-
lng the exhaust systems so that a
portion is dumped directly overboard
and a portion is used to cool the
exhaust system.
Full sea water flow
entering the exhaust system would
create unnecessary exhaust back
pressure.
4. SEA WATER PUMP:
The.s~a wa~er
pump is self priming and
posltl~e
dlsplacement. It is a rotary
pump wlth a nonferrous housing and a
neoprene impeller. The impeller has
flexible vanes which wipe against a
curv~d
cam plate within the impeller
houslng, producing the pumping action.
On no account should this pump be run
dry.
There should always be a spare
impeller and impeller cover gasket
aboard.
5. SEA WATER PUMP IMPELLER REPLACEMENT:
The following instructions are general
and indicative only. Specific instruc-
tions where applicable may be packaged
with your replacement impeller.
a. Remove the front cover taking care
to salvage the gasket.
b. Remove the impeller by pulling
straight outwards, parallel to
the pump shaft.
This is best
done with a pair of pliers ap-
plied to the impeller hub.
c. Coat the replacement impeller
and the chamber into which it
mounts with grease.
d. Carefully align the impeller key
way, or other locking mechanism,
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