Engine whistling - very weird

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et0609

Active Member
Joined
Jun 18, 2006
Messages
324
Location
Highlands
Car
E350d
My car has been making a very strange noise lately. This only seems to happen when the car is switched off after being driven and locked. It does not start making this noise immediately, but after maybe 10 mins and continues for over an hour, eventually it stops. There are no warnings or messages and the car runs fine. I have taken it to the dealership who after being unable to replicate it (not sure why as it does it every time its driven), fobbed me off with some rubbish about a pressure relief valve. The video is of someones elses car on youtube but the noise is identical to mine. Any ideas on this or has someone else experienced this?

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Since it's usually fans that go on running after the engine is switched-off, I can only assume that one of the fans has a failing bearing, or failing motor (or otherwise rubs against something when spinning?).
 
Markjay’s theory sounds valid. You could test that theory by locating the fuse for the fan and taking it out while you can hear the whistling to see if it stops.

The dealership’s pressure relief valve theory could also be right if it’s causing the coolant to boil and what you’re hearing is similar to a kettle boiling. Have a look at your temperature gauge while the whistling is there. If it’s high then that’ll point you in the right direction.

Good luck, those sorts of things are so annoying aren’t they.
 
Thanks for the advice, I dont think its coolant, as the temperature always looks to be ok, it doesnt get too hot.

But yes, its so annoying!
 
If you stop, lock the car and then wait - does it make that sound immedeately or does it start after a period of a few seconds to say a minute or so? If you unlock the car when the sound is heard - does the sound stop temporarily?

I have an E350 petrol with a coolant circulating pump right next to the expansion container. That pump starts after stopping the (warm) engine, but the pump stops immedeately if the car is unlocked. Then it starts again after a few seconds. I have not had any issues with this pump, but I can imagine what a small electric motor feels about running next to +95C hot coolant...

Another thing I have found is that the passenger compartment blower sometimes runs for an extended period of time after having turned of the car and locked it. It runs at low speed which I beleive is to ventillate/dry up the interior AC radiator in order to prevent algae build-up as a result of remaining condensated water in the AC radiator. My C207 has a vortex preventing air intake baffle that can be removed making it is possible to see if the blower rotates...
 
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You're correct, it does not do this when stopped and unlocked, but after stopping, locking and maybe a couple of minutes later, the noise starts. It then continues on and off for an hour or so.

I have noticed that the whistling noise lasts about 3-4 seconds, then stops for about 1 second, then another 3-4 seconds and so on. Towards then end of the hour or so it does it, the whislting noise only lasts a second or 2, so gradually lasts less and less time. I was thinking it must be a seal or gasket, perhaps leaking air as there is no fluid or liquid anywhere under the car.
 
My car does the same - but without the whistling noise.

So - I would put a bet on the external water circulating pump next to the coolant expansion vessel. It should only take a few minutes of DIY to replace...
 
Thanks very much, will take a look at the weekend.
 
When I discovered this noise I struggled to find any info online that pointed me in the direction of a solution, apart from the help of people on this forum. So after several months of interaction with the dealer and cancelled visits due to the poor weather I finally have had the car fixed. I thought I would share this as anyone else with this problem may find this useful. The dealer did replace the water circulation pump as suggested by Uky but the actual answer was the 12v battery. The battery was always showing as partially charged in the App and the start/stop function was not working but in addition to this the battery voltage was causing a solenoid valve on the coolant system to not fully open and the spring going and down very quickly was causing the strange noise. So problem solved and happy the car is perfect now.
 

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