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 TM 5-1940-277-20
TM 1940-20/2
1-12. MK1 ENGINE COOLING SYSTEM.
The coolant circuits and components are shown on preceding page.
a.
Flow During Engine Warm Up
During this type of operation the system is divided into two principal circuits (1) and (2), which are
almost independent of each other with a third circuit (3) providing de-aeration.
(1)
Thermostatically Controlled Cylinder Block Circuit
In this circuit, water is circulated by the conventional engine mounted water pump `A',
which directs water into the block and then the cylinder head. From there, the water is
taken by duct `B' to the water jacket around the exhaust manifold. A small pipe `C' connects
to the header tank to allow air to escape during filling, also providing a small flow when
the engine is running so that continuous de-aeration takes place. From the exhaust
manifold jacket, the water flows through pipe `D' to the full flow bypass thermostat. If the
water temperature is below the thermostat opening temperature, the flow passes through
pipes `E' and `F to the engine oil cooler, and then through pipe `G' to the pump `A', thus
completing the circuit.
(2)
Low Temperature Circuit
A pump `H' directs water through pipe `J' to the gearbox oil cooler, and then through pipe
`K' to the charge air cooler. The water then flows through pipes `C, `M', and `N' to the
`remote cooler'. From the `remote cooler' the water returns to the pump `H' via pipe `P'. A
small pipe `Q' allows air to escape from the circuit when filling, and provides continuous de-
aeration when the engine is running.
(3)
Header Tank Circuit
The header tank receives a small flow of water through pipes `Q' and `C', and returns
make-up water through pipe `R', close to the inlet to pump `A'.
b.
Flow When Engine Coolant Is Up To Normal Operating Temperature
In this condition the flows described in a(1), a(2) and a(3) above continue, but an additional flow
circuit is set up which connects the two circuits (1) and (2) together:
(1)
Low Temperature Flow Diluting Thermostatically Controlled Cylinder Block Circuit When
the engine thermostat valve opens, water flows through pipe `S' and then into pipe `N'
leading to the remote cooler. The water lost from the engine cylinder block circuit is
replaced by water from the low temperature circuit, passing through pipe `T' and diluting
the `by-pass' water flowing from `E' and `F'. By these means the temperature in the cylinder
block circuit is controlled by the thermostat.
1-13. MK2 w/SABRE ENGINE COOLING SYSTEM.
a.
Primary Engine Cooling System. The primary engine cooling system is identical for both port and
starboard engines. Coolant flows from the primary water pump through the engine block to the
header and through the exhaust manifold to the thermostat where it is diverted to the keel cooler
or to the primary water pump. The coolant diverted to the keel cooler flows through the keel cooler
to the oil cooler and back to the primary water pump.
(1)
Primary Water Pump - circulates the coolant through the primary cooling system.
(2)
Header (Expansion Tank) -acts as a reservoir for both primary and secondary engine
cooling systems. The cap is fitted with a relief valve to prevent damage to the system by
overpressurization.
(3)
Exhaust Manifold - serves as a heat exchanger where coolant flowing through the exhaust
manifold cools the exhaust gases from the engine.
(4)
Thermostat - operates as a heat sensitive valve, diverting coolant either to the keel cooler
or to the primary water pump.
(5)
Keel Cooler - serves as a heat exchanger where coolant from the primary cooling system is
circulated through the rear keel cooler and is cooled by the raw water under the hull.
(6)
Oil Cooler - serves as a heat exchanger where oil from the engine is circulated through the
oil cooler and is cooled by the coolant.
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