2006 C8 - Mysterious Squeal

[Mike M.]

My 2006 petrol C8 has done only 23000 miles, but has recently developed a very annoying squealing noise. The noise only occurs when the engine is at normal operating temperature and is ticking over. On start up the noise is not able to be heard, and does not appear during the warm-up period. Once normal engine temperature is achieved I can hear it, but only on tick-over - raising the engine revs only slightly is enough to make the noise disappear. Any ideas would be much appreciated please - it's driving me to drink!!!

[paul.h]

If it is from the engine, I think you will need to have a good listen with the bonnet up to try and pinpoint the area. Things that squeal tend to be rotating bits like pulleys on the drive belt and timing belt and possibly the clutch release bearing. Other rotating bits in the belt area are the water pump, alternator and air con compressor. You may also need to consider an air leak in a hose somewhere. If it only occurs when moving and is not from the engine, you may need to consider the brakes.

[Mike M.]

Thanks Paul, but I think I've covered all those - depressing the clutch and loading the alternator make no difference to the noise, and if it was due to a fault in the water pump/alternator/air con comp I would expect the squeal to be present all the time. As I said, the noise is only audible when the engine is at normal operating temperature and at tick-over revs. That's the most puzzling bit - why only under those circumstances?

[paul.h]

If it is nothing rotating then if low down see if it is an exhaust joint, expands when hot and engine shakes a bit more if low revs - when making the noise push the tail pipe and see if it changes.

 

The C8 is known for timing belt failures but I do not know if it applies to the petrol engines since ones reported on here have been diesels. Whilst yours is low mileage, at 7 years old it ought to be checked. You may be able to remove the top belt cover to have a look.

[Mike M.]

It's been a long time I know, but suggestions so far have not solved or identified this VERY annoying problem. However, purely as a result of ONE comment on a general motoring problem forum I have discovered that if I slightly lift the oil dipstick, or crack open the engine oil filler cap whilst the squeal is audible it immediately stops and only recommences when the dipstick is replaced or the filler cap tightened. As a result of that I'm now thinking that the noise is somehow related to the engine breather system. Does that give anyone food for thought??

[paul.h]

Interesting, I had a problem on a Saab once of a whistling noise and that was a hose on the cam cover that had gone soft and collapsed and as air was sucked through it the noise was made, similar to a baloon when the neck is pulled tight as air blows out. So when you let in air to the breather system by lifting the dipstick or opening the oil filler cap, you are reducing the vacuum in there which will reduce any flow of air that is being sucked in or through the system.

 

Have a look at all the hoses for any that are soft, have splits along them or at the ends. At tickover, the manifold vacuum will also be at its greatest so you could also have a look around the manifold as far as the throttle body/plate for a leak and maybe try something like wd40 sprayed on the joints to see if it makes a difference. When warming up the throttle plate may be open slightly to increase the revs which would reduce the manifold vacuum. You could also clean the throttle plate/body in case it is fouled with carbon.

[Mike M.]

Update:- Nothing's changed since my last post. Done all the checks that have been suggested, Been to three local repair garages, including the Citroen dealership (who were most helpful as usual by wanting £35 up front before even listening to my problem), but without any success. The "squeal"still starts as soon as the engine reaches normal operating temperature and is on tickover, and only disappears when either the engine revs are increased slightly or the engine oil dipstick/filler cap is cracked open. Things are getting a little past merely annoying now because the time has come to change vehicles so I really need to get rid of this noise once and for all - would YOU buy a used car making this strange noise?......Any advice no matter how far fetched would be much appreciated!!!! Thanks, Mike M. 

[paul.h]

If it is not a moving part, I suspect there could be a gap that opens up a bit when the engine is hot and lets air through. It must be between the throttle plate and engine or connected to this area so is at max vacuum when on tickover.

 

- Maybe the egr valve does not fully seat, if there is a valve.

- You could try a spray around all the possible joints that could be leaking to see if the noise changes.

- Also see if using the brakes changes the noise since the servo system is under vacuum.

- Do the engine revs change when the oil filler/dipstick are cracked open ?

- A clean of the throttle plate/body using a carb cleaner or a rag damp with white spirit/turps to remove any carbon build up may help if it is the sound of air going through it. When the engine is warm the throttle will close more on tickover so the plate/body gap will reduce.