To access the thermostat, you will need to:
* Remove the air filter box.
* Disconnect the coolant temperature sensor.
* Remove the two bolts that hold the coolant outlet housing to the cylinder head.
* Carefully remove the coolant outlet housing, taking care not to spill any coolant.
* The thermostat is located inside the coolant outlet housing.
Once you have removed the thermostat, you can inspect it for damage or wear. If it is damaged or worn, it should be replaced. To install a new thermostat, simply reverse the steps above.
Here are some additional tips for replacing the thermostat on a 1990 VW Cabriolet:
* Make sure that the engine is cool before you begin work.
* Drain some of the coolant from the radiator before you remove the coolant outlet housing.
* Use a new coolant temperature sensor when you reinstall the coolant outlet housing.
* Fill the radiator with new coolant and bleed the system according to the manufacturer's instructions.
