Humming Noise after engine off

[knowlep]

Hi all
As a newbie to this site I have trawled the threads but not found the answer I need so here goes:-
When I turn off the engine on my ML270 (W163 2001) there continues a whirring or humming sound from under the bonnet like a small fan or similar for a few minutes until it eventually stops. Even with the key out, doors locked and walking away it continues.
I'm told it's normal but my brain being as it is just wants to know what it is thats going on?
Also what is the round black plastic ball about the size of a large tennis ball on the right side of the engine bay for?
Anyone know
Cheers
Knowlep

 

[Dieselman]

The noise is the eelctric cooling fan I suspect and the ball is probably the vacuum reservoir.

 

[Dragon]

I have no experience with an ML but I have seen earlier this year the cooling fan was constantly on in a W202 because of an electrical fault. Maybe it could because the engine is above a determined temp it remained switch on until it cools down. If it switch off thereafter there is nothing to worry about. I do noticed sometimes after a long drive in my W202 the oil pump keep operating with ping sound, I know it quite normal.

 

[knowlep]

Thanks for replies

Thanks for the replies - good to know you guys are out there.

 

[skemball]

Mines makes a ticking/whirring sound in the engine bay for a minute or so even if i switch the ignition on then off wothout starting. Not tracked down where its coming from but its allways done it.

 

[Bazzle]

Have you opened the bonnet??

Take a hose and put one end to your ear and have a sniff around if you cant see where the noise is coming from.

Take a pic of the part and post it here so we can work out for you what it is

Bazzle

 

[knowlep]

The Answer Is Here !!

Ok the humming noise is now fully answered.
It turned out to be the Auxillary Water pump wearing out. The brushes were that far gone that they had virtually disintegrated.
This pump runs on electrically for a few minutes after the engine is turned off to circulate coolant in order to prevent heat sink and hot spots.
The pump is a sealed unit but being a little dextrous and innovative I've parted the workings and I've temporarily replaced the brushes with some I cut down from an old electric drill and it's working fine at the moment but I will replace is ASAP.
So there y'go.

 

[mattkh]

The pump is a sealed unit but being a little dextrous and innovative I've parted the workings and I've temporarily replaced the brushes with some I cut down from an old electric drill and it's working fine at the moment but I will replace is ASAP.
So there y'go.

Hi
Well done.
Did you take any photos.
These pumps are about £100.

 

[knowlep]

Picture Attached of pump

Pic here (I Hope)
http://www.mbclub.co.uk/forums/attachment.php?attachmentid=10511&stc=1&d=1210007889

 

[ian4c]

Hi
Well done.
Did you take any photos.
These pumps are about £100.

Most interesting. I have noticed this or a similar noise after I switch off my ML 270. The noise seems to come from the round ball on the left wing area. Sometimes just as the noise stops a different tone sounds.

My ML has done 43000 miles so I would not have thought that my pump brushes would have worn out.

Not sure where the pump is located. Perhaps you could advise Knowlep.

Thank you for the help.

Ian

 

[glojo]

Have you opened the bonnet??

Take a hose and put one end to your ear and have a sniff around if you cant see where the noise is coming from.

Take a pic of the part and post it here so we can work out for you what it is

Bazzle

Hi Bazzle,
I know exactly what you meant but your post still made me smile and I thank you for that.

Put one end of a hose to your ear and with the other end, have a sniff...... around

Do our ears smell that much?

I am NOT criticising you, I fully understand your post and what you mean, it is just my silly sense of humour kicking in.

Thank goodness you did not suggest sticking one end into a different orifice! No pictures please. Tooo much information

Thanks again
Regards
John

 

[GazCaff]

Ok the humming noise is now fully answered.
It turned out to be the Auxillary Water pump wearing out. The brushes were that far gone that they had virtually disintegrated.
This pump runs on electrically for a few minutes after the engine is turned off to circulate coolant in order to prevent heat sink and hot spots.
The pump is a sealed unit but being a little dextrous and innovative I've parted the workings and I've temporarily replaced the brushes with some I cut down from an old electric drill and it's working fine at the moment but I will replace is ASAP.
So there y'go.

Very innovative! I like people who are willing to apply a little Heath and Robinson every now and again.

 

[SSBB]

I have a strange whining noise in my car as well. Got the wife to get out and listen but it dissapeared. It started again when she got in....still cant find the cause!

 

[knowlep]

Ian4C
The pump is located on the inner wing by the battery opposite the air cleaner element retained with a large rubber boot.
The first sound you hear when switching off if the air evacuation cycle from the "Black ball" which lasts about 5 seconds. Then if you "feel" the auxillary pump it should be running (assuming the engine is hot) and continue to run for about 4 or 5 minutes. (Don't burn yourself)
My brushes were worn out at 59K miles and my mates were certainly gone at 79K miles.
The interesting thing is that one brush wears more than the other and if you gently press the electrical connector laterally in towards the wing (you may have to press reasonably hard but with care not to damage anything) it flexes its plactic brush pack casing, which is the lower part of the pump, just about a thou or two which brings the worn brush back into contact with the commutator and starts the motor running. This proves whether or not it's past its best.

 

[ian4c]

Many thanks for the information Knowlep. Great help and information. Of course it's easy to see when you are in the know (no pun intended).

The air evacuation cycle from the "Black ball" sometimes lasts longer than 5 seconds. And today even when the engine was quite hot I heard no noise or could feel no movement on the pump.

I am sure all is well but will keep my eye on it. Thank you.

Ian