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4.1.3. Thermostat
1) General descriptions and main data
The thermostat maintains a constant
temperature of coolant(90 ~95
c
) and
improve thermal efficiency of the engine
by preventing heat loss.
Namely, when the temperature of
coolant is low, the thermostat valve is
closed to make the coolant bypass to
directly enter the water pump; when the
coolant temperature rises to open wide
the thermostat valve, the bypass circuit
is closed and the water passage to the
radiator is opened so that the coolant is
forced to flow into the radiator.
Item
Specifications
Type
Wax-pallet type
Open at(
C
)
83
Open wide at(
C
)
95
Valve lift mm
8 or more
- 82 -
EQM4004I
<Figure 4-3> Thermostat
Thermometer
Wood plate
Bar
EFM2055I
<Figure 4-4> Checking thermostat
2) Inspection
(1) Check the wax pallet and spring for damage.
(2) Put the thermostat in a container of water, then heat the water slowly and check temperature with
a thermometer. If the valve lift is 0.1mm(starting to open) at temperature of 83
C
and 8mm or
more(opening wide) at temperature of 95
C
, the thermostat is normal.
3) Replacing thermostat and precautions for handling
(1) Precautions for handling
The wax pallet type thermostat does not react as quickly as bellows type one to a variation
of temperature of coolant. Such relatively slow reaction is mainly due to the large heat
capacity of the wax pellet type thermostat. Therefore, to avoid a sharp rise of coolant tem-
perature, it is essential to idle the engine sufficiently before running it. In cold weather, do
not run the engine at overload or overspeed it immediately after starting off.
(2) When draining out or replenishing coolant, do it slowly so that air is bled sufficiently from
the entire cooling system.
(3) Replacing thermostat
If the thermostat is detected defective, replace with a new one.
From cooling
water pump
To bypass
tube
To radiator
Bypass
valve