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SECTION R
COOLING SYSTEM (EXTERNAL)
1.
DESCRIPTION:
Westerbeke marine diesel engines are
equipped with fresh water cooling.
Transfer of heat from engine fresh
~ater
to sea water is accomplished
1n 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
well as heat developed by friction
.
.
1S 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 prevent overheating in the exhaust
manifold. As the engine warms up, the
thermostat begins to open up allowing
full flow of engine fresh water thru
the external cooling system.
3.
SEA WATER CIRCUIT:
The sea water flow is created by a
positive displacement neoprene inpeller
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.
Generally it is better to have as few
devices on the suction side of the sea
water pump as possible to preclude
priming difficulties.
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
tran~mission
oil cooler if present
and 1f 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
water flow is divided prior to enter-
ing 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
pos1t1~e
dlsplacement. It is a rotary
pump w1th a nonferrous housing and a
neoprene impeller. The impeller has
flexible vanes which wipe against a
curved cam plate within the impeller
housing, 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
~ol!owi~g
instructions are general
and lnd1cat1ve only. Specific instruc-
t~ons
where applicable may be packaged
w1th 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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