Troubleshooting Renault engine noise

Here's something that's been driving me crazy over the last week. My Renault Scenic (diesel) has developed an odd and annoying noise. It's directly related to engine speed (i.e. dies away as I move the transmission to neutral and let the revs drop.

I've videoed the problem/noise below, in the hope someone can suggest what the problem might be. You're listening for a highish pitched whistling/rubbing noise.

Renault Scenic belt system noise for troubleshooting from Steve Litchfield on Vimeo.

I thought it might be the belt itself, but the addition of a little talc didn't help. Anyone ever seen/heard this before? Possibly a dry bearing somewhere, but where do I start looking? Alternator? Water pump?

The car only had a new cam belt fitted a year or so ago, complete with new tensioners.

Many thanks if you can rack your brains for some pointers here!

[SOLVED] Turned out to be the tensioning pulleys, one of which did indeed have a dry bearing. New kit fitted and all quiet now 8-)


I'm no expert with diesels, but...

Just to be clear, you're referring to a whine that's more or less in the background, a bit obscured by the roar of more typical engine bay noises...right?

If so, I'd check for two things: (1) contamination or damage to the pulleys and/or the belt's drive-surface; (2) signs of lubricant splash from pulley drive-shaft(s) at their bearings.

Presumably, those checkpoints are self-explanatory -- if not, send a tweet. Anything along those lines could cause a shrill, 'whizzing' sound that's both high-pitched and RPM-variable.
Thanks. there are about 5 or 6 elements in that belt system, so just a question of working through them, I guess!
Yeah, do that. :-)

It's an educated guess but if I had to bet, I'd say you could solve this problem simply by replacing the belt and cleaning/de-glazing the pulleys.

At high RPM, you can get this kind of noise from any of several interactions between the belt & pulley(s). If you have time, Google 'supercharger belt whine'.

So, you're looking for (1) schmutz on the moving bits; (2) a pulley-shaft with signs of (imminent) bearing failure and/or (3) drive-belt damage/deterioration.
So you think it's unlikely to be the alternator or water pump on the way out?
jonquirk said…
As you have had the cambelt and its tensioners changed recently we can focus on the accessory belt and its pulleys. Carefully placing a probe on each component in turn as the engine is running may reveal which item is worn(alternator, water pump, idlers, etc). Once you have a suspect to examine more closely remove the belt and turn that part by hand: noise and roughness may then be clearly heard/felt.

(I had something like this on my Xantia and it turned out to be one of the idlers. My mechanic used a long screwdriver as a stethoscope to find which one.)
Dave said…
Steve, not sure if the diesels are the same as petrols in layout, but I have a petrol megane, and it could be the Air Con Compressor?
Just a thought.
Well yes, it's in the pulley system, but when air-con isn't engaged, a clutch stops it from actually needing to turn. I think!
Dave said…
mine still turns as its connected to drive belt but is worse when the aircon button is pressed. But at nearly 400 quid to replace it. I just open the window.

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