my997c4

I have a 2006 C4 with 49K miles and from a cold start, I began hearing this intermittent grinding noise on top of the regular engine hum during idle. This strange sound would go in and out just like how a locomotive would sound with intermittent whinning noise (which sounds very painful to me by the way). I took off the Air intake assembly to inspect the serpentine belt and the various pulleys, bearings and snubbers. They all seemed fine. I've attached a link to the video so you all can see.

thanks

Zeus993

I think you'll need to run it into a shop. How long has it been like this?

Edgy01

It sounds like a bad bearing on one of the pulley driven accessories.

avader906

most likely water pump and/or belt tensioner.

997_rich

Agree- sounds like a bad pulley driven item. Maybe the idler pulley. Did you record in stereo? it sounds almost like it's coming from the left.

You can take the belt off an spin each one to test. Or you can use a piece of 1/2" rubber hose like a stethescope. Or you can even take a long screwdriver and use the handle against your ear and rest the tip against each pulley driven item (start by putting it against the alternator etc). Sounds crazy but it works well.

Macster

Sounds like an accessory drive is noisy. My WAG would be the water pump.

Before you do anything you might want to drop the oil filter housing and dump the oil and element into a *clean* drain pan. What you see or don't see determines what you do next.

If the oil is clean of any debris one 'trick' is to carefully note the belt's routing (take a pic!) and its direction of rotation (pic!) and then remove the belt. You can start the engine and run it a while like this.

If the noise is absent then almost certainly it is an accessory drive (or idler/tensioner roller bearing) that is making the noise.

If the noise is still present, you're done. Take the car to a qualified shop for diagnosis.

Check the belt. My experience when a water pump got a bit noisy was the belt developed a sharp inside edge due to excessive bearing play at the water pump which allowed teh belt to mistrack and rub against the side of the grooved water pump pulley.

With the belt removed you can test each accessory drive for any signs of play. There may not be much but you'll have probably one 'bad' one and the rest good and by comparing the play of each if there's one with any play that's the suspect drive.

Check the idler roller and tensioner bearings for excessive play or roughness or signs of seal degradation.

Sincerely,

Macster.

Weissach

Disconnect the belt and run it for a few seconds(when cold). You'll know in an instant if it's one of your accesories

AYHSMB

Water pump failure is semi-common for 997's. Alternator failure is also not unheard of. So hopefully it's one of those.

Spiffyjiff

i dont want to hijack the thread, but if i may please ask a quick (stupid ) question: obviously the routing is paramount, but is the belt's rotation uni-directional?? i changed mine a few months ago but didnt pay attn to the direction nor can i find any directional markings on the old one.

thanks in advance.

Edgy01

The routing is defined on this related thread:

https://rennlist.com/forums/997-foru...failure-2.html

997_rich

Usually when they'll uni directional they have the little arrows printed on the belt. i can't remember if this one is uni or bidirectional but you can just check the one on the car. it takes a long time for the markings to wear off. I'm pretty certain that it's bi-directional.

Macster

A new serpentine belt can be installed to run in either direction. But my info is that once the belt has run in a direction if it is removed and reinstalled it should be installed so it continues to run in the same direction as before.

Sincerely,

Macster.

Hartdude

Sounds like a lower idler pulley to me. We've done two of those on 997s in the last month.

997_rich

Let us know what the root problem is because this is a fun game for us. It's like a motorhead's version of trivia.

my997c4

didn't get a chance to update you guys on this matter....didn't get back to it till last night but here are my observations:

- so i ran the engine for a few moments without the belt and the strange noise was not present which was great so it must be one of the accessories as all of you mentioned.
- next I spun each pulley / idler / accessory and nothing popped out of the ordinary in terms of resisting rotation or excessive play/wobbling.
- so i reconnected the belt and started the engine again to diagnose further. Took a really bright lamp and shown it on the fully exposed rotating belt pulley/idlers etc... as the engine was running. What i noticed is that there was a slight wobble (the kind only you would notice if you were to shine intense light on) on the water pump pulley and it synched with this aweful sound. So I went underneath placed my ear relatively near the pump housing which is visually accessible directly beneath the car. The noise definitely was coming from it because when i touched the housing (that's because I didnt have a stethoscope) I felt this vibrating sensation that again, synched up with the aweful noise. I also tried resting the tip of a long screwdriver and placing the back of the handle against my ear and confirmed this grinding vibration. Also tried this trick on the rest of the accessories (alternator, compressor, idler, tensioner..etc...) what I heard were slight and smooth vibrations - 10 folds less intense than with the water pump.

So I ordered a new pump arriving tomorrow morning and a video I found to perform the replacement...stay tuned..