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LP Engine G430(3.0L) Cooling System
Thermostat
Figure 9-6 Thermostat
When theA pellet-type thermostat in the coolant outlet
passage controls the flow of engine coolant to provide
fast engine warm-up and regulate coolant
temperatures. A wax pellet element in the thermo-stat
expands when heated and contracts when cooled.
The pellet is connected through a piston to a valve.
When the pellet is heated, pressure is exerted against
a rubber diaphragm to force the valve open. As the
pellet cools, the contraction allows a spring to close
the valve. In this way, the valve remains closed while
the coolant is cold, preventing circulation of coolant
through the radia-tor. At this point, coolant circulates
throughout the engine to warm it quickly and evenly.
As the engine warms, the pellet expands and the
thermostat valve opens, permitting coolant to flow
through the radiator where heat passes through the
radiator walls. This opening and closing of the ther-
mostat permits enough coolant to enter the radia-tor to
keep the engine within operating temperature limits.
Thermostat Test
To test the thermostat opening temperature, use the
following procedure:
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).
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