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Replacing the Thermostat

Model: Volkswagen Jetta A4, MK 4 - Years 1998-2005
Part: Thermostat

This maintenance must be carried out when the engine is cold as removing the thermostat will cause coolant to spill. The thermostat is located at the front left of the engine (when viewed from the front), just above the air conditioning compressor, behind the alternator: you will need to remove the alternator to access the thermostat. Once the alternator is removed, you can detach the fitting where the thermostat is inserted and replace it with a new one (it is recommended to also change the O-ring gasket). After positioning the new thermostat, reassemble everything, restore the coolant level, and start the engine to check the operation of the new thermostat: after the fan comes on, check the coolant level again.

Updated on 7 February 2026 by ScegliAuto

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