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L4 MARINE ENGINES-W.3
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along the keel of the craft. Prior to reaching the
water pump, the coolant passes through the lubri-
cating oU cooler which is fitted as standard equip-
ment to engines employing this type of cooling
system. The coolant then enters the engine at the
forward end of the cylinder block and is expelled
at the forward end of the cylinder head. From
the cylinder head the water is discharged back
into the keel pipes via the exhaust maillfold cool-
ing jacket. It will be observed that this is a closed
circuit type of cooling system, the water in the
keel pipes being cooled by the water through
which the craft passes.
With this type of cooling system, a thermostat
is fitted as optional extra.
Information regarding dimensions of Keel Pipes
may be obtained on request from
.Service
Divi-
sion, Perkins Engines Limited, Peterborough.
Indirect Cooling System (Heat Exchanger).
This type of cooling system utilised in con-
junction with a heat exchanger, incorporates two
separate water pumps, viz. the rubber impeller
and centrifugal types.
The rubber impeller type pump is used to
circulate sea water through the heat exchanger
which is affixed to the front of the cylinder head.
Overboard discharge is taken through the exhaust
manifold cooling jacket. The lubricating oil cooler
which is standard equipment with indirectly cooled
engines is fitted to the front end of the engine
sump and is on the suction side of the sea water
pump.
Circulation of the closed fresh water system is
etIected by means of the centrifugal pump which
is belt driven from the crankshaft pulley. Water is
drawn from the heat exchanger and enters the
cylinder block at the rear of the water pump.
Af ter circulation through the engine, the water is
expelled from the front of the cylinder head back
into the heat exchanger.
The top part of the heat exchanger fornls a
header tank fjr the fresh water and a pressure
type filler ca{f with overflow pipes is provided.
The valve in the cap operates between 3* and
4i-lbs./sq. in. (.23-.30 kg/sq. cm.) A thermostat
is supplied as standard for this type of cooIing
system.
Water Pum~.
From the foregoing it will be apparent that alt
L4 Marine engines, irrespective of application,
incorporate the rubber impeller type of water
pump, while those engines utilising indirect (heat
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