Bad Belt Tensioner?

[Anigrelli132]

Is this a bad belt tensioner or is this normal?engine has a very light random idle roughness and AC doesn't work since the compressor clutch doesn't engage but this happens with the AC on or off. Its a 2005 Jetta Wagon with BEW engine.

 

[DivineChaos]

Can't upload it to YouTube? Easiest is to pull the serp belt and check pulleys and run it with it the belt off.

 

[Anigrelli132]

Oops wrong link here is the YT link

 

[DonL]

I have a 2005 Jetta wagon with BEW. It turns out taking the serpentine belt tensioner off and replacing it is pretty simple if you have a 16mm open end wrench. Youtube will show you how.

 

[Anigrelli132]

I have a 2005 Jetta wagon with BEW. It turns out taking the serpentine belt tensioner off and replacing it is pretty simple if you have a 16mm open end wrench. Youtube will show you how.

Yea I read up on it seems simple enough. It's my girls TDI so she wants me to do as much research as I can. It seems like a bad tensioner to me but wanted some feedback from others before I told her to order it.

 

[DonL]

I was replacing the alternator and I learned a lot. Good luck with it.

 

[Nuje]

I'd check the alternator pulley first - make sure it's able to "freewheel" in one direction; that's a more common issue with serpentine belt roughness.
Remove the belt. Lock the alternator (put a screwdriver in it to prevent it from turning. See if you can freely move the pulley one direction (the freewheeling), but not the other. If it's locked in both directions, replace the pulley.

Replacement is relatively easy in the BEW with the alternator up and front (compared to ALH), but requires a special tool (Metalnerd for the proper kit, but if time is of the essence, I think Amzn has a kit that'll do the trick as well).

 

[PakProtector]

Tensioner issues are often traced back to a locked up one-way clutch on the alternator. These liddle Diesels have too much rpm variation due to compression and then firing that the one-way is needed.
cheers,
Douglas

 

[Gruni14]

Is the belt or tensioner bouncing around? If so, that could be the issue causing the vibration. Could be a bad engine mount too.

Observe the belt tensioner. Replace the Idler tensioner first if it's bouncing around ...bc it's fairly inexpensive. If it still bounces around ...or fails (bounces) within a month or two afterwards, then the guys are right, it's likely the alternator pulley. Been there myself.

This video kind of illustrates the issue:

 

[DivineChaos]

Hearing that tensioner rattle makes me wonder if the one on my mk6 is going bad.have to look. Their is 150k on it.

 

[Anigrelli132]

Thank you all for the help. I'm going to test everything hopefully tonight or tomorrow, will find out of I need to order the pulley. I have the tensioner ordered will be here during the week.

I do know the wishbone mount is orginal but the upper engine mount is new per the PO. I think the tensioner is orginal though which makes me suspect it being bad but will do all the tests anyways.

Cheers!

 

[Anigrelli132]

Got the belt off tested the alternator pully it spins one way but requires a little force to spin while holding the shaft in place. Spins freely without issue when not holding the shaft in place.

Tested the tensioner seems very easy to move for the first few mms then gets very tough does look orginal though.

Not sure if the alternator pulley needs to be replaced think I'm going to go with what I was originally going to do and what gruni14 suggested.

Took a few videos for reference will edit this with the link when I have the videos up on YT.

Edit: Alternator Pulley Tensioner

 

[KrashDH]

In most cases, when the alternator pulley starts to go and gets worse, this is what causes the tensioner to fail since it's working overtime.

If you're in there with the belt off, I would do the pulley while you're at it. I neglected this and it blew a new tensioner.

 

[Anigrelli132]

Yea thats what I thought and also might do the belt as well

 

[Anigrelli132]

So got the new tensioner in but it has a smooth pulley vs the stock grooved pulley. Does that matter?

 

[Metal Man]

The tensioner should have a smooth pulley.

 

[PakProtector]

The tensioner should have a smooth pulley.

You sure? This is a BEW...belt has grooves on both sides...

Douglas

 

[Anigrelli132]

You sure? This is a BEW...belt has grooves on both sides...

Douglas

Right that's what I thought the stock one has grooves while the replacment gates' is smooth. Very confused but kermatdi has the replacment one with a smooth pulley as well.

 

[Metal Man]

The serpentine belt tensioner on a BEW is smooth. I have seen a lot of them and they are smooth. They do show marks on them from the belt ribs and may even wear into the belt a bit.

 

[Nuje]

Everywhere I look, the current part number is 038903315AE; and doing an image search on that part number yields smooth pulleys everywhere.

 

[Anigrelli132]

Yea thats what I've seen too only 1 that had the grooves but was a different bolt/mounting pattern. I'm just going to mount it and forget, its just weird that the one on it now has grooves for the belt. Curious maybe PO put a different one on that clearly wasn't the right one