Today our Renault Scenic 1.9DCI (2001/2) developed a rattling noise on idle which disappears totally when the revs are increased. The car runs perfectly. The noise is coming from the area around the alternator where there is a large belt tensioner. I have applied pressure to the tensioner (using a screwdriver) in an attempt to increase the pressure on the alternator belt and this stops the noise, so I think it may be the tensioner.
However, I have read elsewhere that the alternator on this engine has a clutch which, if faulty, can cause exactly the same noise/rattle/symptoms. The alternator is working fine.
Does anyone please have any comments/ideas on this matter as to weather I should be looking at having either the alternator or the tensioner replaced (or both) ?
Thankyou
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Hi,
I guess I have exactly the same noise and when tensioner is pressed the noise goes. I have fitted a tensioner but noise is still there. I am hoping you have cured your noise and can shed some light on this problem.
I would be very grateful for your reply.
Thankyou
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mig123
This is depressingly common. It is nearly always caused by the failure of the previously stated one-way over-run clutch built into the alternators drive pulley. If it gets really bad the tensioner whips about so viciously that it breaks up.
New pulleys are available, but require a special splined tool to install. Usual route is a re-con alternator.
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Please do not ignore this rattle, as a friend of mine had exactly the same problem on the same model.
The over-run clutch on the alternator fails in two ways, firstly, it pulses and causes the serpentine auxiliary belt to resonate - even though the belt tensioner is doing it's job. This 'pulsing' which can be seen as an oscillation in the belt causes the belt(multi ribbed) to ride up over the grooves in the pulleys. If you are very lucky, the belt slips off the ends of the pulleys and falls off in one piece, normally only chewing up one or two 'ribs' of the belt.
If you are unlucky, the belt partially fails and the remains whip round and are dragged into the crank shaft pulley - then around the toothed crankshaft timing wheel. This then snaps the timing belt.
I know this because this happened to my friends car at 50mph.
Result - bent valves and a massive £1700 bill from Renault main dealer to rebuild the cylinder head. A huge task and something like 12 hours labour. Having said that, they had the car for 10 days waiting for parts!
Renault know these alternator pulleys are causing problems, yet I am not aware they have changed the design.
I mentioned two ways the over-run pulley can fail. The pulsing from the over- run clutch mechanism in the pulley can damage the alternator bearings as well, causing further problems down the line.
If you try to change alternator/pulley and the belt, be aware, the auxilliary belt tensioner is a real s*d to release. If it's like the one on my mates car, there is no means of relaxing the tensioner as it is a simple jockey wheel with a powerful spring attached. A Renault Technician told me they all hate working on these type tensioners because of the design. New tensioners about £90! are supplied pre-strapped up, so you only need to position the belt correctly before releasing strap.
Once again, get the alternator checked ASAP.
Spanner
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This has happened to 3 of our Kangoo 1.5 dcis at around 70000 miles and also to a customers at 30000 miles whose unfortunately took the cambelt with it. They last approx 70 miles with the rattle then it goes pop.
Get it checked sharpish!
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