This guide provides a detailed walkthrough for replacing the thermostat on an Audi A4 B6 1.8t. The thermostat, part number 06B-121-111-G (or the updated -H version), is a crucial component for maintaining optimal engine temperature. This DIY guide will help you save money and understand the process. This process requires basic mechanical skills and tools. Always consult your vehicle’s repair manual for specific torque specifications and safety procedures.
Draining the Coolant and Accessing the Thermostat
Before starting, ensure the engine is cold. Begin by draining the coolant. Remove the engine undertray and the coolant reservoir cap. Locate the coolant temperature sensor near the lower radiator hose, unclip it, and drain the coolant into a suitable container.
Next, disconnect the upper radiator hose. Detach the small hose connecting the reservoir to the upper radiator hose. Then, release the metal clip securing the larger hose to the radiator and carefully pull it off the hard pipe.
For better access, remove the driver’s side headlight. Loosen the clamps on both ends of the intake hose (connecting the throttle body to the intercooler) and remove it.
Removing Components for Thermostat Access
Disconnect the electrical connector and remove the four 5mm hex bolts holding the throttle body in place.
Loosen the serpentine belt tensioner using a wrench and carefully slip the belt off the alternator pulley.
Remove the four bolts securing the alternator to its bracket. Disconnect the electrical connector and the grounding strap from the alternator. If the battery is still connected, insulate the grounding strap to prevent accidental shorts.
Remove the two 6mm hex bolts holding the vertical support piece connecting the intake manifold to the engine block. Remove the bolt securing the metal coolant pipe to the thermostat housing and the bolt attaching the pipe to the top of the oil cooler. This may require removing the thermostat first to fully detach the pipe.
Replacing the Thermostat
Disconnect the upper and lower hoses from the thermostat housing and unplug the electrical connector. Remove the two bolts holding the thermostat to the engine block.
Install the new thermostat with a fresh O-ring, ensuring the old one is removed. Lubricate the new O-ring with coolant before installation. Reassemble everything in reverse order of disassembly.
Final Steps
Double-check all connections and ensure all bolts are tightened to the correct torque specifications. Refill the cooling system with the appropriate coolant mixture and bleed the system to remove any air pockets. After starting the engine, monitor the coolant temperature gauge to ensure the new thermostat is functioning correctly.
