S8 Belt Squeal Fix: Tensioner Pulley Troubleshooting

I had nearly identical issues with my 2008 S6 4.2L about a year ago. Having some experience with engine noise problems, I immediately recognized that distinct belt squeal during cold starts. The symptoms matched perfectly, the serpentine belt was slipping, especially noticeable when using accessories. The engine performance drop was also a telling sign. After inspection, the tensioner pulley was indeed worn out, causing improper belt tension. The repair involved: Replacing the complete belt tensioner assembly, Installing a new serpentine belt, Checking other pulley alignments Total cost was 455 Euro including parts and labor. The repair took about 3 hours and completely resolved the belt squeal. The engine has been running smoothly since, with proper belt tension and no noise issues. Before giving more specific advice, could you share: Current mileage on your S8, When was the last belt service done, Are there any other unusual sounds or vibrations, Have you noticed any fluid leaks near the belt area This information would help determine if your issue is isolated to the tensioner or if other components might need attention.

Thanks for the detailed response. My S8 currently has 134067 KM and the last major service including timing belt replacement was done 45000 KM ago. The idler pulley and tensioner bearings are definitely making more noise now than before. No other unusual engine noise or vibrations noticed, and automobile maintenance records show no previous issues with the belt system. The area around the belt drive is clean with no visible fluid leaks. Based on your experience, it seems my symptoms match what you encountered. This helps confirm my suspicion about the tensioner assembly being the likely cause. If the repair cost and timeframe are similar, that would be manageable for my situation.

Thanks for providing those details. Yes, this further confirms what I experienced with my S6. Given that your timing belt was replaced 45000 KM ago, the wear pattern on the tensioner assembly matches typical deterioration rates I've seen. The noisy idler pulley and tensioner bearings are classic indicators of wear, just like what I dealt with. In my case, waiting too long led to increased stress on other belt drive components, so addressing it sooner rather than later is wise. Since your automobile maintenance history shows no previous belt system issues and the area is clean, you're likely looking at a straightforward tensioner replacement job, similar to my repair. The labor costs tend to be consistent since access to the belt drive system is the same between our models. One tip from my experience: while the system is exposed, have them inspect the water pump and other accessory pulleys. The cost to check these during the belt tensioner replacement is minimal compared to a separate service later. Based on current parts prices, you should expect repair costs close to what I paid (455 Euro), possibly slightly higher due to inflation since my repair last year.

That makes a lot of sense about checking the other components while the belt drive system is exposed. Given the similarity between our vehicles and symptoms, I feel more confident now about proceeding with the repair. The serpentine belt issues and engine noise you described match my situation perfectly. I appreciate the tip about inspecting the water pump and accessory pulleys during the service. Better to catch any potential issues while everything is apart rather than risk another repair session later. The estimated repair cost seems reasonable considering the work involved. I will schedule the tensioner replacement this week and make sure to request that full inspection of the belt drive components. Will definitely have them pay special attention to the idler pulley since it's already showing signs of wear. Thanks for sharing your repair experience, it has been really helpful in understanding what I'm dealing with.