SL55 strange noise/issue - possibly S/C

[Dickster]

Hi there,

I've had my SL55 since May 2019, and hadn't really stretched its legs until recently.

So, it practically redlined through the gears, and was running great. Then all of a sudden it changes up a gear, then back down, and appeared to be down on power.

At the same time I hear a continuous "whooshing noise", not unlike air escaping from a tyre - I had the window slightly open.

I slow down. Gradually, the noise disappears. Now, under 30 mph I got no noise. But over 30/35 I get a regular release of air from somewhere - the intermittent release increases with speed.

Otherwise, the car starts and runs fine. No warning lights.

The sound is not quite the same as a wastegate, but that's the nearest I can think of.

Any ideas? Bypass valve?

I did think it was a split hose, but note that the intercooler is W/C!!

Thanks

Rich

 

[flowrider]

Could be the supercharger making the whooshing sound. The gearbox "issue" may just be it needs an oil change, when was it last done.

 

[Petrol Pete]

You had the car for 7 months before you decided to 'give it some beans' ?? Now thats what I call self control !

 

[Dickster]

Its not the usual S/C noise, its really loud. Where can air escape from?

I've given it some beans before, but this was a proper shakedown!

 

[Cyclone1]

Does it make the noise only under acceleration?

 

[Cyclone1]

Check your TB hose is not split (normally underneath), or not fully connected (clip not securing it fully).

 

[Dickster]

Good question. I believe it does it on a constant throttle too. I was a few miles from home when it happened and tried to feather it up to a decent speed, but anything over 30/35 induced the noise. I might be completely off, but it did sound like the offside front tyre area. And at one point when it happened, I heard a sound not unlike something on the tyre (or the tyre shredded) hitting the inner wheel arch - flapping. Strangely, the noise appears to go in time with the rotation of the wheel. I've checked the tyre, no loss of pressure there. And no sign of damage.

I might try and get a recording this weekend.

 

[Dickster]

Check your TB is not split (normally underneath), or not fully connected (clip not securing it fully).

Are they known to split? Thanks

 

[Cyclone1]

Not really but I had to replace mine on my first CLS55.

On reading your last comment ref tyre / wheel arch then it may be something else. But with the whooshing noise you’re describing and when on acceleration then it makes me think induction related of some sort.

 

[Dickster]

Thanks, I'll check it. The tyre, wheel arch may be a red herring, and might just be where the noise escapes from..

I agree, if I had to put money on it, I would go for induction.

 

[moodi]

Smoke test the intake system

 

[Dickster]

I've not had time to investigate yet. But the smoke test is a good idea.

Also, can I turn the SC off by pulling a fuse? If I pull SC cooler pump fuse that will stop the SC from operating? the Then I could try it without boost?

Thanks

 

[ChrisHampshire]

Easiest way to disable the s/c is to remove the belt. It takes a few seconds...

 

[Dickster]

Thanks. Doesn't the belt drive other stuff? I want to be able to test drive it...

 

[ChrisHampshire]

No, there are 2 belts - one belt drives only the s/c and the other drives everything else

 

[Dickster]

Great, thanks

 

[alabbasi]

No, there are 2 belts - one belt drives only the s/c and the other drives everything else

There's a dual pulley that drives both the sc and the accessory belt. It's 1/2 plastic and 1/2 metal. Watch out for this one as the plastic pulley can grenade and take out both belts (ask me how I know). This pulley can make a racket and should be replaced at around 65k miles. Replacements are quite costly but it needs to be done.

 

[Dickster]

that's good to know thanks - i'm just over 65k

 

[ChrisHampshire]

There's a dual pulley that drives both the sc and the accessory belt. It's 1/2 plastic and 1/2 metal. Watch out for this one as the plastic pulley can grenade and take out both belts (ask me how I know). This pulley can make a racket and should be replaced at around 65k miles. Replacements are quite costly but it needs to be done.

Spot on. Mine went at 73k miles. In my case, fortunately, only the front half of the pulley detached and it managed to do this (and throw the s/c belt of course) without affecting the other belt. So the car was still driveable. It cost £800 to fix (including > £20 just for the bolt - it's a torque-to-yield bolt).

 

[Lenny63]

The double idler pulley can be replaced now with independent pulleys for the plastic and replacing the bearing for the metal...tried and tested numerous times in the american 113k forums...I've bought the pulley already it came from usa and was about £35..the bearing for the metal isnt too expensive either

A lot better than the £800 mercedes charge for the complete double idler