Attention! The illustrations show the thermostat removed from the housing. In A-class cars, the thermostat and housing form a single unit.
The principle of operation of the thermostat
As the engine temperature rises, the thermostat opens a large coolant circuit.
In this case, the thermostat spring is gradually stretched and the length of the thermostat increases (see distance a and b in illustration 5.0).
If, due to a malfunction, the thermostat does not work, the engine will overheat.
This position is signaled by the coolant temperature gauge on the instrument panel, the arrow of which enters the limit temperature range. At the same time, the radiator remains cold.
A faulty thermostat may remain open after the coolant has cooled.
This thermostat defect can be determined by the fact that the engine does not warm up to operating temperature or by a decrease in the intensity of interior heating in winter.
Examination
Attention! This check only allows you to determine whether the thermostat opens when heated, and also closes when it cools.
1. Remove the thermostat.
2. Check the position of the thermostat through the connecting pipe.
3. Heat the thermostat housing by immersing it in a container of water. In this case, the thermostat should not touch the walls of the container (see illustration).
4. Monitor the temperature of the water in the tank with a thermometer. As soon as the water in the tank reaches the boiling point, carefully remove the thermostat housing and check the height of the thermostat through the connecting pipe.
The thermostat should open and the hole for the coolant to flow to the radiator should be completely free. If not, replace housing and thermostat.
5. Make sure the thermostat closes completely when it cools down. Otherwise the thermostat replace.