Raatlingnoise

[dekhelia]

Hi all, got a rattle noise from the aux belt end ofthe engine on my Golf 2.0TDI. I'm suspecting air con pump, alternator, or one of the idlers or tensioner in this area. It only rattles when cold - as soon as it's warmed up the noise goes. The rattle is worse when I turn on the heater fan, and only happens at idle. If I increase revs, the rattle goes whether engine is cold or warm....any ideas?

*title should read 'rattling noise'!

[dekhelia]

What a nightmare. So I took off the aux belt, and the rattle disappeared. I changed the aircon pump, put the aux belt back on: rattle still there. Ok, so changed the aux belt tensioner: rattle still there. Changed the crank pulley: rattle still there. Only thing left to do is change the alternator, as that's the last part left in the aux belt system. I've got an alternator to swap into the car, so I'll report back on what happens.

Makes me think, though. Obviously I've had the alternator off when I was removing the aircon pump, and tbh it seemed fine - no play in the pullley, very smooth and noiseless to turn...I mean, if it's not the alternator, what the hell else could it be??

[tditaff]

Perhaps a mechanics stethoscope would help identify the noise source...

[dekhelia]

Perhaps a mechanics stethoscope would help identify the noise source...

Yeah, I've been using one .... the noise of the tensioner clacking against its metal stop sort of obliterates all other sounds, though.

The tensioner undulates rhythmically, which to me would suggest that a pulley is out of whack somewhere. The only pulley left in the system that hasn't been swapped out is the alternator - but as I say, it seemed to be fine when I span it, no noise or roughness.

What really baffles me is the behaviour of the tensioner when I turn on the heater fan: it clacks like mad against the stop, I just don't see how the fan blower could cause this.

[tditaff]

The pulley on the alternator is clutched - a type of one way pulley to even out the lumpy diesel engine vibrations, if that fails it causes the tensioner to oscillate /bounce which could well be the issue you describe!
I think it needs a special tool to remove the pulley from the alternator. Or you could get a whole combo from a scrappy/ebay.

Regarding the fan blower, it could be that the extra current draw from the alternator is causing the extra vibrations from the failed pulley...

[dekhelia]

Thanks. I sure hope this is the cause. I've got a spare alternator, which I'll put in on Thurs. I'll report back with results....

[Crasher]

As taff says, the tensioner should not be clacking around like that, you can buy new one way clutch pulleys quite cheaply.

[dekhelia]

Thanks for the info Taff and Crasher. I'd have never known the alternator pulley was the culprit (hence why I spent an hour swapping out the crank pulley, aux belt tensioner and aircon pump - and then stood there scratching my head as the noise continued. I think I should have been a bit more logical, really....but there you go: I was throwing parts at it like a dealership mechanic!

Anyway, all well again - the replacement alternator has solved the rattling.

Thanks again chaps.