Hissing noise after switch off - 07 320CDI Diesel Esate

[ramer]

Noticed recently, that after turning the engine off, there is a hissing noise from somewhere under the bonnet that lasts for about 15 seconds, then dies away over 3-4 seconds. Sometimes think I can hear it randomly inside the car when driving, again last for maybe 20 seconds then fades. No other apparent symptoms, no liquids appearing anywhere - any ideas???

By the way, which "w" variant engine am I likely to have?

Thanks.

 

[Tinkerer]

Do you have the aircon turned on? this can usually be heard hissing through the vents.

 

[ramer]

Do you have the aircon turned on? this can usually be heard hissing through the vents.

Aircon IS turned on, but it's much more like the hissing of a radiator or punctured tyre, neither of which it appears to be.

I can imagine it might be some sort of leak from the Air Con, but there are no smells or odours at all, and you can hear the same sound standing next to the wing/bonnet.

 

[GordonTarling]

The sound is from the aircon - it will hiss for a short while after stopping. Your car is an S211, with v6 engine (OM642).

 

[ramer]

The sound is from the aircon - it will hiss for a short while after stopping. Your car is an S211, with v6 engine (OM642).

And I assume from what you're saying that's normal?

Thx re the S211 info.

 

[b1g1an]

Really, I've had cars with aircon for thirty years and never heard any hissing like that.

I'd assumed it was the SBC releasing the pressure.

 

[SL300-24]

I think there is no SBC on a 2007 car.......

 

[b1g1an]

Good point, my other thought on mine was the air suspension but am only guessing.

 

[DRBC43AMG]

You have a snake living under the bonnet...

 

[sspeed]

Really, I've had cars with aircon for thirty years and never heard any hissing like that.

Neither have I !

 

[developer]

Does the car have Airmatic, identified with a switch behind the gearstick, as per the photo?

 

[ramer]

No, definitely no switch like that behind the gear-selector....

 

[GordonTarling]

Yes, quite normal. I used to hear it often on my 'old' 211, but not so noticeable on the current 211.

 

[b1g1an]

What is it though, mine does it when I lock it and coincides with the suspension lowering if it was set high/soft.

 

[developer]

What is it though, mine does it when I lock it and coincides with the suspension lowering if it was set high/soft.

As does mine.

 

[ramer]

No Airmatic (as far I know!) on my car, so it's not that...

 

[Charlie87]

Mine does this aswel, 2008 S320, I assumed it was the air suspension exhausting excess pressure?

 

[Ian Donkin]

Does the car have Airmatic, identified with a switch behind the gearstick, as per the photo?

Off topic I know, but what is that wheel control for to the passenger side of your (stop/start) gear lever?

Cracking spec'd car John

 

[Mark68]

My S211 does the same thing, at the front. I'm fairly sure it's the air suspension.

Mind you, I've been told that it shouldn't do it and it may indicate that I have a problem with the airmatic.....

 

[developer]

Off topic I know, but what is that wheel control for to the passenger side of your (stop/start) gear lever?

Cracking spec'd car John

Sorry Ian, I missed this - it's the Distronic thumbwheel for setting the distance from the vehicle in front - the car then maintains this distance as other vehicles enter/leave the radar beam.