Possible worn out serpentine tensioner?

[hansmoman]

Our '05 Golf TDI just passed 110k and I was asked to look at it by the driver. Seems to be having a few separate issues, but there was some rattling sounds coming from the engine bay along with squealing on the power steering which both seem to only happen on the driveway (according to the driver).

I took a look at it with the engine running and the tensioner bounces quite violently. The belt doesn't feel all that tight to me but I cannot really measure that other than by feeling. Here is a video I found on youtube that shows another wobbly tensioner:

http://www.youtube.com/watch?v=wBOW6x99hCI

Our seems to wobble a bit more than shown in the video with the AC off, and with AC on it wobbles perhaps 2 or even 3x as much. The belt itself is brand new, I just replaced it 5000 miles ago. I don't recall the guides specifically mentioned replacing the serp belt tensioner (I did replace the timing belt tensioner), but maybe I should have.

Could the belt slipping be causing a squeeling in the power steering? Or what could that otherwise be?

[YMZ]

Quite often on these cars, a failing alternator pulley causes the tensioner to bounce excessively. The pulley design is directional - meaning it's supposed to slip in one direction. If that function has ceased to work, then you're looking at other problems that will come your way.

Remove the serpentine belt and check the alternator pulley... it's supposed to turn the alternator shaft when turned clockwise, and let the alternator "run" when you counter that rotation... (use the inertia of the alternator rotor...)

Hope this helps,

Yuri

[shuswap]

If the serpentine belt fails it can dislodge the camshaft belt in some worst-case circumstances, resulting in valve-piston contact.
If this is a PD BEW engine I'd check the camshaft and lifters for wear(loss of the lobe chamfer ...read the FAQ for details)
It takes approx 30 minutes to get the valve cover off and is vital to catch before the lifters fail and a valve drops

[charby]

I have had two of the Alternator pulley fail and both have caused the tensioner to jump violently. If the pulley is OK it should only move 5- 7 mm when running. Also this can create a rattle noise similar to a loose lid on a jar.. You need a special tool to R & R the pulley.

[hansmoman]

Sorry for the slow response, I just managed to fix it. It was indeed a seized alternator pulley. Put a new one on and its back to normal. Big thanks for that heads up as I would never have realized that was the problem!!