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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 22732
Experience:  BEng hons Mech engineering, in auto industry 22 years
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2006 S320 CDI, squeal from engine at 1500 rpm, does it every

Customer Question

2006 S320 CDI, squeal from engine at 1500 rpm, does it every time from idle. Had new charge air pipes, solid and flexi. New turbo and gaskets. Still does it, just have to blip the throttle and it squeals
Submitted: 4 years ago.
Category: Mercedes
Expert:  Matt replied 4 years ago.


I'd first try removing the auxiliary drive belt and turning every pulley and ancillary ( power steering pump , alternator etc) by hand. All should turn easily (with the exception of the AC pump) with no grittyness or wobbly pulleys- If you do find a sticky pump / alternator then it should be replaced or repaired

If the engine is stone cold you can briefly run it with no belts to see if the noise changes or has gone away, this will help show if an ancillary is the issue

Examine carefully the condition of the bottom / crank pulley as these are composite construction with a rubber element and its possible this rubber is breaking up and allowing the two metal portions to move.

Customer: replied 4 years ago.

Tried running without the serpentine belt before the turbo was changed and the noise was there. Definitely coming from around turbo/front engine area. Tried listening around with an engineers stethoscope and can't pin it down. High shrill squeal (similar to a failed water pump) when throttle blipped from idle to approx. 1500 rpm. Visual examination of the crankshaft pulley shows nothing, with the bottom covers removed I can see the pulley with the engine running and there is no deflection when the engine is revved.

Expert:  Matt replied 4 years ago.

in that I'd suspect an issue with the cam chain tensioner if there's any hint of a ringing or rattling coming from the front cover this would back this up

what can happen is the cam chain tensioner becomes blocked up and then allow the the chain to rattle and squeak so its well worth trying an oil flush treatment and then fresh oil to see if this helps
Customer: replied 4 years ago.

I've had the stethoscope on the front cover and cam covers while having someone rev the engine and can't hear anything, plus there is no rattles or unusual noises when the engine is idling. Today I drove the car without putting any load on the engine and the noise was not present at any road speed, it only occurs when the engine is asked to work or revved from idle. I've also dropped all the plastic under body panels and had a good listen.

Expert:  Matt replied 4 years ago.

OK in that case its possible that this is an airleak, as its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.