Chapter 6 Cooling Water System
6. Thermostat
6.
Thermostat
4LHA Serie.
6-1
Functioning
of
thermostat
The
thermostat opens and
closes
a valve according to
changes
in the temperature of the fresh water inside the
engine,
controlling the volume of water flowing to the heat
exchanger
from the cylinder
head,
and in
turn
maintaining
the temperature of the fresh water in the engine at a
con-
stant
level.
The
thermostat is bottom bypass type. It is located in a
position connected
with
the cylinder head
outlet
line at
the top of the top of fresh water pump
unit.
When
the fresh water temperature is low (75.0 ~ 78.0
o
C or
less),
the thermostat is
closed,
and fresh water goes from
the bypass line to the fresh water pump intake and cir-
culates
in the engine.
When
the fresh water temperature exceeds the above
temperature, the thermostat opens, and a portion of the
water is sent to the heat exchanger and cooled by sea
water, the other portion going from the bypass line to the
fresh water pump intake.
The
bypass line is closed off as the thermostat valve
opens,
and is completely closed when the fresh water
temperature reaches 81.5
0
C (valve
lifts
4mm (0.1575in.)),
sending
all of the water to the heat exchanger.
Thermostat cover
Thermostat valve
From
cylinder head
Impeller
To
heat exchanger
Thermostat valve
From
cylinder head
When
valve is opened (by-pass passage is closed)
6-2
Thermostat
construction
The
thermostat used in this engine is of the wax pellet
type,
with
a solid wax pellet located in a small chamber.
When
the temperature of the cooling water
rises,
the wax
melts and increases in volume. This expansion and
con-
struction is used to open and close the valve.
6-3
Characteristics
of
thermostat
Opening
temperature 71
"C
Full
open
temperature
85
0
C
Valve
lift
at
full
open
8 mm (0.31 in)
When
valve is closed (by-pass passage is opened)
6-14
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