Removing and installing thermostat: Audi A4 B5 (AEB, AFB, AGU, AJK, …)

🧭 Before you start

Drain the coolant, remove the bumper and set the lock carrier to service position. Remove the viscous fan pulley, poly V-belt, tensioner, power steering pulley, engine covers, air intake parts, toothed belt covers and vibration damper. Lock the belt tensioner with T40011, ease the belt forward, and remove the thermostat housing and thermostat. Refit with a new O-ring, pre-tension the roller to 15 Nm, reassemble and fill the cooling system.

Fits: Audi A4 B5 (8D)

• Opens: coolant
• Timing position: the crankshaft or camshaft is set and locked during this job
• Special tools named: 17 mm ring spanner, torque wrench
• Renewed: o-ring

Don't miss

• Mark the poly V-belt's running direction before removal; running it backwards can cause breakage.
• The viscous fan pulley has a left-hand thread; unscrew it clockwise.
• Compress the oil-damped belt tensioner slowly; it only moves under steady pressure.
• Do not let the toothed belt slip off the tensioning roller, or timing must be reset.
• Renew the thermostat O-ring and pre-tension the roller to 15 Nm.

Written for this job from the workshop steps below · TorqFix editorial.

🔧 Engine codes this applies to

🔩 Torque settings

Values can differ between engine variants — check the code stamped on your block.

ℹ️ Always cross-check the exact figure against your vehicle's factory manual before final tightening — a wrong torque can damage the engine. These values are extracted from workshop data and may not cover every variant or revision.

📋 Procedure

1. Drain off coolant .
2. Remove front bumper 63.
3. Move lock carrier to service position 50.
4. Use open-end spanner3312 to unscrew viscous fan pulley in clockwise direction (arrow) (left-hand thread) while counterholding with pin wrench3212. [Note: Before removing, mark direction of rotation of poly V-belt with chalk or felt-tipped pen. If the belt runs in the opposite direction when it is refitted, this can cause breakage.]
5. Turn the tensioner in the direction of the (arrow) using a 17 mm ring spanner to slacken the poly V-belt.

6. Lock tensioner in position by inserting locking pin3204 in locating holes (arrows).
7. Remove poly V-belt.
8. Unscrew bolt (arrow) and remove tensioner for poly V-belt.
9. Unbolt power steering pump pulley (arrows) (counterhold with pin wrench3212).
10. Unfasten screw connections (arrows) and detach engine cover panels (A ... C).
11. Unplug electrical connector at output stage N122(item 3) and at output stage 2N192(item 4).
12. Unplug electrical connector (5) at air mass meter G70.
13. Move wiring harness at air cleaner housing clear.
14. Detach air intake hose (6) at air mass meter G70.
15. Unplug vacuum hose (1).
16. Unscrew nut (2) and remove air cleaner housing with air mass meter G70.
17. Loosen quick release fasteners (arrows) and remove cover for cylinder head cover (right-side).
18. Unscrew bolts (arrows) and remove bracket.
19. Disconnect air intake hose (4) from air pipe.
20. Unscrew bolts (1 ... 3) and (5) and remove air pipe (left-side).
21. Disconnect air intake hose (1) from air pipe.
22. Remove bolts (2 … 5) and take out air pipe (right-side).
23. Remove bolts (1 … 3) and take out toothed belt cover (left-side).
24. Remove bolts (1) and (2) and take off toothed belt cover (top right).
25. Release retaining tabs (3) and (4) and detach toothed belt cover (bottom right). [Note: Central bolt does not have to be loosened when removing vibration damper.]
26. Remove bolts and take off vibration damper. [Note: Disregard (arrows).]
27. Unbolt bottom section of toothed belt cover (bottom arrows). [Note: Do not remove poly V-belt pulley for viscous fan.] [Note: The toothed belt tensioner is oil-damped and can therefore only be compressed slowly by applying constant pressure.]
28. Turn toothed belt tensioning roller (1) clockwise in direction of (arrow) using an 8 mm Allen key until tensioning lever (2) compresses tensioner (3) far enough for the pressure piston to be locked with locking pin T40011.
29. Release pressure from the toothed belt tensioning roller.
30. Pull toothed belt forwards slightly on tensioning roller and right camshaft sprocket (arrows), but do not pull off completely.
31. ⚠ Timing must be re-adjusted if toothed belt has slipped off tensioning roller . Follow all instructions for removing and installing toothed belt . — Detach coolant hoses (1) and (5) from thermostat housing.
32. Unscrew bolts (2), (3) and (4) and detach thermostat housing.
33. Remove O-ring and thermostat. [Note: Renew O-ring.Hose connections and hoses for charge air system must be free of oil and grease before assembly.Secure all hose connections with the correct type of hose clips (same as original equipment) Parts catalogue.]
34. Clean and smoothen sealing surface for O-ring as required.
35. Install thermostat.
36. Install thermostat housing.
37. ⚠ Timing must be re-adjusted if toothed belt has slipped off tensioning roller . Follow all instructions for removing and installing toothed belt . — Using an 8 mm Allen key, turn toothed belt tensioning roller (1) clockwise in direction of (arrow) until the locking pin T40011 can be removed.
38. Apply torque wrench to hexagon socket of tensioning roller.
39. Pre-tension tensioning roller by applying a torque of 15 Nm. — 15 Nm (11 lb-ft)
40. Install vibration damper .
41. Install poly V-belt .
42. Install viscous fan .
43. Install lock carrier with attachments 50.
44. Install front bumper 63.
45. Fill cooling system .

🎬 Video walkthrough

Independent video tutorial by AUTODOC (YouTube) — a helpful visual companion to the steps above.

How to change engine thermostat on AUDI A4 B5 Saloon

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