Service manual

G420F(FE) Service Manual Chapter 3. Engine Mechanical System 57
Thermostat
The thermostat is the wax pellet type. A jiggle
valve (which improves air bleeding during water
supply) is provided on the flange part. When the
thermostat is closed, the circulation of coolant is
stopped, thereby making warm-up faster.
Operation
When the temperature of the coolant is low, the
valve is closed by the spring, with the result that the
coolant circulates within the engine, without passing
through the radiator.
When the temperature of the coolant rises and
reaches a certain specified temperature, the valve
opens and the coolant also circulates through the
radiator.
When the temperature increases further and
reaches a certain specified temperature, the valve
opens fully, allowing even more coolant to circulate
through the radiator.
Thus, in this way the degree of valve opening is
varied according to the temperature of the coolant,
and the temperature of the coolant is adjusted by
varying the amount of coolant caused to circulate
through the radiator.
Thermostat Test
To test the thermostat opening temperature, use the
following procedure:
WARNING
The pan, water and thermostat will be very hot
and can cause burns. Do not touch the pan,
water or thermostat. Handle the components
with an insulated device for protection.
1. Remove the thermostat from the engine.
2. Hang the thermostat in a pan of water. Put a
thermometer in the water. Put the thermostat
completely under water. Do not let the thermostat
make contact with the pan.
3. Put heat to the pan of water. Make the water in
the pan move around. This keeps all of the water
at the same temperature.
4. The thermostat must start to open when the
temperature is 82°C (180°F). The thermostat
must be fully open at 96°C (205°F).