Single shaft (SOHC) engines
1. Disconnect the battery from ground.
2. Drain the coolant.
3. Remove the air filter and air ducts (Chapter 4A).
4. Disconnect the hose from the thermostat cover.
5. Remove the camshaft belt, idler roller, camshaft sprocket and rear belt cover (Chapter 2A).
6. Loosen the bolts and remove the thermostat cover from the cylinder head.
7. Pry and remove the thermostat from the cylinder head, paying attention to its location.
Original posted on the website: OpelBook
8. Hang the thermostat in a heated vessel with water and a thermometer (see photo). When the water starts to boil, the thermostat bypass valve should open. Otherwise, replace the thermostat.
9. Check the thermostat valve opening temperature.
10. If the thermostat does not close during cooling, it should also be replaced.
11. Installation is carried out in reverse order. Replace the sealing ring.
Twin-shaft (DOHC) engines
12. Disconnect the battery from ground.
13. Drain the coolant.
14. Disconnect the hose from the thermostat cover (or 2 hoses for 1.8 and 2.0 l engines). On 1.4 and 1.6 L engines, the cover is mounted on a section of the thermostat housing that is secured to the cylinder head. On 1.8 and 2.0 L engines, the cover is attached directly to the cylinder head.
15. On a 1.8L engine, disconnect the wire from the temperature sensor.
16. Unscrew the bolts and remove the cover together with the thermostat. On the 1.8 L engine, the cover is sealed with sealant.
17. On 1.4 and 1.6 L engines, unscrew the bolts and remove the lower thermostat housing from the cylinder head. If necessary, unscrew the temperature sensor from the housing.
18. On a 1.8L engine, unscrew the sensor from the cylinder head.
19. Check the thermostat for proper operation (see above).
20. Installation is carried out in reverse order. Replace the gasket (sealing ring) thermostat. Install the sealant cap on the 1.8 L engine.
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