Sectional view
1
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Feed from the heater core
2
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Return to the heater core
3
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Return to the coolant expansion tank
The thermostat performs two functions.
The first function is the standard function of not allowing coolant to flow to the radiator until the engine has reached operating temperature.
Once the engine reaches operating temperature, the thermostat opens and coolant flows through the radiator.
The second function serves to maintain adequate coolant flow at high engine speeds when the thermostat is not open.
For this purpose, the coolant pressure causes a spring-loaded valve to open from a certain engine speed. This valve opens up the direct route to the coolant pump, as a result of which no coolant is passed through the heater core under these conditions.
If the engine speed and therefore the coolant pressure drops, the valve closes again due to the spring force, thus re-opening the duct to the heater core.
