Audi Q8 Belt Tensioner Causing Cold Start Squealing

Had almost the exact same issue on my 2018 Q7 3.0 TFSI. Based on some experience with belt drive systems, I can say these symptoms are quite typical for a failing belt tensioner. Initially noticed the belt squeal during cold starts, exactly like you describe. The engine noise would get worse in damp conditions. After inspection, my workshop confirmed the belt tensioner had lost its spring tension, causing insufficient pressure on the idler pulley. They replaced both the tensioner and idler pulley as a preventive measure, cost me 455 Euro for parts and labor. Job took about 3 hours. The timing belt was checked but didnt need replacement yet. The squeal completely disappeared after fixing it. Worth noting that letting this go too long risks the belt jumping teeth or failing completely, which could cause much more expensive damage. Could you share: Current mileage? How long has the squealing been happening? Does the noise change with engine RPM? Any vibrations felt through the steering wheel? This info would help determine if your case matches what I experienced and whether other components might need checking.

Last service done at 75000 KM about 2 months ago. Currently at 78616 KM. Just to answer your questions: squeal noise started 2 weeks ago, mainly during cold starts as mentioned. The engine noise is most noticeable at idle and fades around 2000 RPM. No vibrations through the steering wheel. The belt tensioner seems to be the most likely cause since the engine performance remains stable. The idler pulley looks fine visually but might need replacement along with the tensioner as you suggested. Will get it checked this week to prevent any potential belt failure.

Thanks for the update. Those symptoms match exactly what I experienced before getting my Q7 fixed. The fact that your belt squeal goes away above 2000 RPM is particularly telling, classic sign of a failing belt tensioner, just like what happened with mine. My automobile maintenance records show I was at around 82000 KM when the issue started, so pretty close to your mileage. The timing is also similar, mine started with occasional squealing during cold starts, then got progressively worse over about 3-4 weeks. Since your engine noise pattern is identical to what I experienced and your car has similar mileage, Id strongly suggest getting both the tensioner and idler pulley replaced together. The labor cost is practically the same since they are accessing the same area, and it provides better long-term reliability for the belt drive system. Quick tip from my repair experience: while they have the belt off, have them check the water pump pulley for any play. Mine had slight wobble and the workshop caught it during the tensioner replacement, saving me from potential issues down the road.

Thanks for all that detailed input. Your experience really helps confirm my initial diagnosis. Will definitely have them check both the belt tensioner and idler pulley during the repair. Makes total sense to replace both while they are in there, especially at my current mileage. The parts and labor costs you mentioned give me a good baseline for what to expect. My serpentine belt problems sound nearly identical to what you dealt with, the cold start squealing and how it fades at higher RPM. Good call on checking the water pump pulley too. The engine performance staying normal is reassuring, but better to fix this before risking any belt failure. Have booked it in for next week. Will update the thread once I know exactly what they find and what gets replaced. Really appreciate the thorough information about your repair experience, helps a lot with knowing what to expect.