This guide provides a detailed walkthrough for replacing the thermostat on a 2003 Audi A4 1.8t. This is a common maintenance procedure and can be completed with basic tools and mechanical knowledge. The original thermostat part number is 06B-121-111-G, which may have been superseded by a newer revision. Always verify the correct part number for your specific vehicle before ordering.
Draining the Coolant
Begin by preparing the vehicle. Park on a level surface and engage the parking brake. Allow the engine to cool completely before starting. Open the coolant reservoir cap to relieve pressure. Locate the coolant temperature sensor near the lower radiator hose. Place a drain pan underneath, carefully disconnect the sensor, and allow the coolant to drain completely.
Removing Components for Access
Several components need to be removed to access the thermostat housing:
1. Upper Radiator Hose: Disconnect the small hose connecting the coolant reservoir to the upper radiator hose. Then, release the metal clip securing the larger upper radiator hose to the radiator and carefully pull it off.
2. Intake Hose: For better access, remove the driver’s side headlight (optional but recommended). Loosen the clamps at both ends of the intake hose (throttle body to intercooler) and remove the hose.
3. Throttle Body: Disconnect the electrical connector and remove the four 5mm hex bolts securing the throttle body.
4. Serpentine Belt and Alternator: Use a wrench to relieve tension on the serpentine belt tensioner and carefully slip the belt off the alternator pulley. Then, remove the four bolts holding the alternator to its bracket. Disconnect the electrical connector and grounding strap from the alternator. Insulate the grounding strap to prevent accidental shorts.
5. Support Bracket and Metal Hose Bolt: Remove the two 6mm hex bolts holding the vertical support piece connecting the intake manifold to the engine block. Also, remove the bolt securing the metal coolant pipe to the thermostat housing and the bolt on top of the oil cooler. This will allow you to move the hard pipe away from the thermostat.
Thermostat Removal and Installation
Disconnect the upper and lower hoses from the thermostat housing and remove the electrical connector. Remove the two bolts holding the thermostat to the engine block. Carefully remove the old thermostat, ensuring the old O-ring is also removed.
Install the new thermostat with the new O-ring provided. Lubricate the O-ring with a small amount of coolant before installation. Reinstall all components in reverse order of removal. Ensure all connections are secure and tightened to the proper torque specifications.
Final Steps
Refill the cooling system with the correct coolant type and bleed the system according to the manufacturer’s recommendations. Start the engine and check for leaks. Monitor the engine temperature to ensure the new thermostat is functioning correctly.
This guide offers a comprehensive overview of the process. Always consult a repair manual for your specific vehicle model year for detailed instructions and torque specifications. While this guide aims to be helpful, it is not a substitute for professional mechanical advice. If you are unsure about any step, consult a qualified mechanic. Incorrect installation can lead to engine damage.
