Removal and installation the thermostat (Opel Astra J)

The need to replace the thermostat may arise when the engine temperature is unstable: overheating or insufficient warming up.

To check the thermostat on a car, start a cold engine and touch the upper radiator hose with your hand – it should be cold. After the coolant temperature reaches (80±1.5)°C, the hose should quickly heat up, which indicates that the liquid has started to circulate through the large circuit. If this does not happen, remove the thermostat and check its functionality.

You will need: TORX E10 socket head, sliding pliers.

1. Disconnect the wire from the negative terminal of the battery.



2. Drain the fluid from the engine cooling system (see Replacing the coolant).



3. Squeeze the coolant temperature sensor wiring harness connector retainer…





4. …and disconnect the connector from the sensor.



5. Loosen the radiator hose clamp by squeezing its bent ears with pliers, slide the clamp along the hose..



6. …and disconnect the hose from the thermostat housing pipe



7. Unscrew the four bolts securing the thermostat housing to its module…

Note: For clarity, shown with the cylinder head removed.

8. …and remove the housing assembly with the thermostat.

Note: The thermostat and its housing are a difficult-to-disassemble unit. When attempting to remove the thermostat from the housing, the thermostat mounting posts may break off, so replace the thermostat together with the housing.

If you are installing the old thermostat, use a screwdriver to pry up its rubber sealing gasket…



…remove it from the groove of the housing flange…





…and install a new gasket in the groove. If the new thermostat housing does not have a sealing gasket, also install a new gasket. The old compressed gasket may not provide a tight seal when reinstalled.



9. To check, place the thermostat in a container with water heated to 75–78°C. Gradually heating the water, monitor the temperature at which the thermostat valve begins to open.

Note: The cooling system thermostat is considered to be in good working order under the following conditions:

• valve opening start temperature – (80±1.5)°C;
• temperature of full valve opening – 95°C;
• valve stroke (difference in size values A with the valve fully open and fully closed) – 8.0 mm.

If the thermostat valve does not start to open at a temperature of 90°C, then the thermostat is faulty and must be replaced.



10. Install the parts in the reverse order of removal.

11. Fill with coolant (see Replacing the coolant).