Hissing Query

[karozza]

When I switch the car off & get out, I can hear a hissing noise coming from behind the passenger side front wheel. It sounds like air leaking from a tyre but it isn't the tyre & it stops after a while.

Nothing seems to be wrong.

Is this normal or is something going wrong??

 

[renault12ts]

Just a guess, but for clarification...this is the SL we are talking about?

 

[V12]

1. How long is a while?
2. Is this mysterious vehicle fitted with airmatic?

 

[grober]

The sl55 AMG will be fitted with Hydraulic ABC [ ACTIVE BODY CONTROL]----- a hissing noise on parking up is usually a sign that there's air in the system meaning a leak somewhere. Sometimes bleeding the system gets rid of it. People often take the chance to renew the fluid at the same time- a bit like bleeding the brakes. It would appear from this post that its difficult to bleed the system completely.
ABC pulsation damper and Filter DIY repair - MBWorld.org Forums but unfortunately the pictures for it have gone. ABC systems are more common in the USA so I would suggest looking on some of the American forums for more info.

 

[karozza]

Yes, my SL55 AMG has ABC.

Do I have to change the fluid to bleed the system as it is still green which should mean the fluid is still good??

 

[karozza]

I also have a buzzing noise coming from the engine bay when I open the door before starting & when stationary for some seconds, then stops. Is this the ABC pump priming up? It's not there when driving.

 

[grober]

Photo DIY: ABC Fluid Maintenance - Mercedes-Benz Forum
If its light green then it should be fine but you may some to top up?
The buzzing noise may refer to a dodgy PULSATION DAMPER

 

[GordonTarling]

Try doing a journey with the A/C turned off and see if it's still making the noise.

 

[karozza]

Try doing a journey with the A/C turned off and see if it's still making the noise.

AC is not being used on my journeys; just the top down & a V8 symphony!

 

[karozza]

Photo DIY: ABC Fluid Maintenance - Mercedes-Benz Forum If its light green then it should be fine but you may some to top up? The buzzing noise may refer to a dodgy PULSATION DAMPER

The dipstick level is in the middle with engine off after parked for the night which is not exact but, according to my Mercedes mechanic is where he prefers. According to him, they tend to overflow when topped up to the top notch; whether this is true or not is beyond me. We topped up last time as the reservoir was accidentally left slightly open & the fluid overflowed everywhere.

So, should I replace the damper; if replaced, will the buzzing noise go completely or is this a normal procedure when opening the door after some time stationary??

 

[grober]

This is an excellent explanation/breakdown of the component parts of the ABC system. You will need to use the automatic translator in the Google CHROME browser. OLDTIMER: Tipps für Mercedes SL55AMG
e.g. here's one schematic

I would be inclined to try a new pulsation damper+ system bleed .Will certainly do no harm.

ps there appear to be couple of air accumulators one front and one rear to check also

 

[karozza]

So, is the pulsation damper an expensive part to replace? Although the fluid is still green, I'm thinking of doing the part & a fluid flush/change since this is a used car & have no idea if the fluid has been replaced before.

I read that fluid change is healthy & helps avoid damage to the ABC pump.

If i do replace the damper, will the buzzing be eliminated completely or do you still hear it slightly??

 

[grober]

The part required A2203270215 is around £100 in the UK. Whether it will cure your problem I don't know sorry.

 

[maxima]

I know nothing about SL but on me E class I have an air pump for brake assist system which pumps air often. when you open the car or put key in the pump would most likely to start and 'buzz' for about 3 sec. this is normal behavior.

check if that buzzing thing is not whats expected first before you start to replace everything..

see.. all garages are the same.. even if they are good and honest.. once you show them uncertainty and/or profanity of your car knowledge they would gently help you to indulge in your fears.. its simply psychology. not their fault.

you might end buying new SL part by part. because there hissing here buzzing somewhere rattling and with a popping on the top :bannana:

 

[karozza]

I know nothing about SL but on me E class I have an air pump for brake assist system which pumps air often. when you open the car or put key in the pump would most likely to start and 'buzz' for about 3 sec. this is normal behavior.

This seems similar to what I hear as well. I was waiting for someone with an SL to say if they had the same feature. I'll start another topic & include SL in the heading.

I see your point & would check with my mechanic before going to into any major surgery on the car. Just wanted to hear opinions on hear as well to gather more knowledge.

 

[maxima]

Its actually in my car Owner Manual (about the buzzing). Try yours