Suspicious generator belt tensioner behavior

[WeekendDriver]

My belt tensioner oscillates at idle (~720 RPM). Also makes a high-pitched rattling noise. A tad bit more RPMs - 800-850 - and it stops vibrating. I've recorded it on video. Is it normal? Should I replace the tensioner? I don't like the noises it makes, just annoying, even though I don't hear this noise when inside the car with windows up.

All the higher-pitched noise you hear on the video comes from the tensioner: if I loosen it with a wrench, the noises disappear.



P. S. Just replaced the alternator pulley barely 1000 km ago, so I know that's not the problem. The belt was replaced 5000 km ago.

[shurur9]

My belt tensioner oscillates at idle (~720 RPM). Also makes a high-pitched rattling noise. A tad bit more RPMs - 800-850 - and it stops vibrating. I've recorded it on video. Is it normal? Should I replace the tensioner? I don't like the noises it makes, just annoying, even though I don't hear this noise when inside the car with windows up.

All the higher-pitched noise you hear on the video comes from the tensioner: if I loosen it with a wrench, the noises disappear.



P. S. Just replaced the alternator pulley barely 1000 km ago, so I know that's not the problem.

Though I never could see it, My belt tensioner was wobbling and allowing the bando belt to slip off a bit.
After I got a gates belt, the pulley actually sawed the belt down from 6 to 3 ribs.

I read about the tensioner bolt shearing.
I opened the hood, pushed on the tensioner with my finger and the bolt sheared right there in the driveway.

MY Guess: either your bearings are going or the bolt is shearing.
I'd replace the whole damn assembly Asap...with a new bolt perhaps...

GM sells an alternator bolt with the same specs and dimensions as the audi tensioner bolt..but with a hex head..and at an affordable price..EBAY

[Turbo510]

Worn out bearing; they eventually will if used long enough. It's an easy change on the 1.8T, if that is what you have.

[WeekendDriver]

Worn out bearing; they eventually will if used long enough. It's an easy change on the 1.8T, if that is what you have.

That is what I have. Which bearing, though? Which part should I replace?

[EuroxS4]

Its a whole tensioner replaceement.Peace of mind and easy job maybe a total of 5 minutes.3 bolts and your done.I normally take the belt of the alternator and leave it in the car.Install new tensioner.Put the belt on.Then pull the pin and your done.

[WeekendDriver]

Awesome, thank you!

[Turbo510]

..easy job maybe a total of 5 minutes.3 bolts and your done.I normally take the belt of the alternator and leave it in the car.Install new tensioner.Put the belt on.Then pull the pin and your done.

Now the V-6, on the other hand....

[WeekendDriver]

Now the V-6, on the other hand....

He-he.
Sometimes I feel sad I couldn't get a V6 2.5 TDI or 3.0 petrol, but then I realize I'm better off saving that maintenance and fuel cost for something else (and I'm not an aggressive or sporty driver).
Thanks again for the advice, guys. Ordered Gates T38207 tensioner, and replacement does seem a breeze (except some careful management of the retention pin required).

[WeekendDriver]

Replaced the tensioner (with Gates T38207). I think it oscillates somewhat less now, but it's not as steady as it is at higher RPMs. And some rattling noises are gone, but some still remain, which is odd - previously, I could only hear the engine's purr when I loosened the belt with a wrench, but now I do hear extra sounds that I previously attributed to the tensioner. Perhaps, my engine makes those noise when cold and stops when it's warmed up. Gotta experiment more.
All in all, it seems that the replacement wasn't justified, but it's good to be certain about a part.

[shurur9]

Replaced the tensioner (with Gates T38207). I think it oscillates somewhat less now, but it's not as steady as it is at higher RPMs. And some rattling noises are gone, but some still remain, which is odd - previously, I could only hear the engine's purr when I loosened the belt with a wrench, but now I do hear extra sounds that I previously attributed to the tensioner. Perhaps, my engine makes those noise when cold and stops when it's warmed up. Gotta experiment more.
All in all, it seems that the replacement wasn't justified, but it's good to be certain about a part.

Though perhaps not an issue..consider the tensioner bolt.
I salute your attention to detail.

[WeekendDriver]

Though perhaps not an issue..consider the tensioner bolt.

Oh yes, you were talking about that recently! It slipped my mind the first time, but now's definitely the right time to figure it out. Which bolt do you mean? Probably not the mounting bolts because there are three of them, not one?..

I salute your attention to detail.

Thanks! Honestly, this is probably not the #1 thing I should have turned my attention to, but I don't like foreign noises from under the hood, and it's such an easy replacement that I just decided to go ahead and tick this item off the list.

[5ktq]

The tensioner back and forth wobbling is normal, but more pronounced when the overrunning alternator pulley has seized.

see eg. this video

https://www.youtube.com/watch?v=4EXYP1CmL9Q

You say you've replaced that though. I would check the idler pulley I guess (the one not on the tensioner, between the AC & PS pulleys).

[WeekendDriver]

Interesting video, thanks! Didn't expect the decoupler's design to matter so much. Yes, I've just replaced the alternator pulley with a (hopefully) original INA part, the old one really has seized.
How can I check the idler pulley, what should I check it for? Make sure it spins easily?