Chapter 6 Cooling Water
System
_6_.
_T_h_er_m_os_t_a_t
___________________________
3,4JH3(B)(C)E
6. Thermostat
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 maintain-
ing the temperature of the fresh water
in
the engine at a
constant 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°C
~ 7s.o·c
or less}, the thermostat
is
closed, and fresh water goes
from the bypass line to the fresh water pump intake and
circulates
in
the engine.
When the fresh water temperature exceeds the above
temperature, the thermostat opens, and a portion of the
water ls 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°C
(valve lifts 4mm (0.1575in)),
sending all of the water to the heat exchanger.
-
Impeller
When valve is closed
(by-pass
passage
is
opened)
6-12
To
heat
exchanger
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
Full
open
temperature
Valve
lift
at
full
open
By.pass
valve
lift
By.pass
valve
close temperature
75~78"C
90'
8mm
3.7mm
a1.s·c
Printed in Japan
Hl;'IISHJ-H8009
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