Humming e350
Thread Starter
Senior Member
Joined: Jul 2007
Posts: 488
Likes: 37
From: Albuquerque, NM
2014 e350
Humming e350
After ignition on - then off - cold engine not started: my (new to me) 2014 e350 makes a faint humming sound from the engine compartment - hood closed - that continues for about 30 minutes and then quits.
Same thing after turning off after driving.
Any idea what causes this?
Is it normal?
Any thoughts will be greatly appreciated.owns
Same thing after turning off after driving.
Any idea what causes this?
Is it normal?
Any thoughts will be greatly appreciated.owns
Super Member
Joined: Dec 2015
Posts: 599
Likes: 237
From: Suburban Maryland
2023 E 450 Sedan. 2018 GLC 300. 2013 E 350 Coupe (retired)
Similar to my 2023 E 450. I hear similar noises. Sometimes if you just walk next to it with the key in your pocket it starts to stir. The car is just singing the blues when not being driven 😑. Actually there are electrical components at work I believe. Fuel pump, cooling fan for the screens and God knows what else. It is a computer on wheels after all. Nothing to worry about, just don't sit there and drain the battery!
Last edited by smiles201; Aug 7, 2025 at 07:53 PM.
Out Of Control!!
Joined: Apr 2019
Posts: 11,923
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
COMPUTER ON WHEELS
Similar to my 2023 E 450. I hear similar noises. Sometimes if you just walk next to it with the key in your pocket it starts to stir. The car is just singing the blues when not being driven 😑. Actually there are electrical components at work I believe. Fuel pump, cooling fan for the screens and God knows what else. It is a computer on wheels after all. Nothing to worry about, just don't sit there and drain the battery!
Out Of Control!!
Joined: Apr 2019
Posts: 11,923
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
HEAT SOAK REALITY
After ignition on - then off - cold engine not started: my (new to me) 2014 e350 makes a faint humming sound from the engine compartment - hood closed - that continues for about 30 minutes and then quits.
Same thing after turning off after driving.
Any idea what causes this?
Is it normal?
Any thoughts will be greatly appreciated.owns
Same thing after turning off after driving.
Any idea what causes this?
Is it normal?
Any thoughts will be greatly appreciated.owns
1 - the high pitch hissing every 30 seconds for 20mn
2 - The quiet hum non-stop for 15mn
Both of these rumblings are side effect of engine accumulated extreme heat.
1- this is high pressure fuel rail venting extreme pressure back into tank
2- This is the HL fan running to cool module heated by the engine extreme heat.
These two issues serve as heat markers. When heat soaks are disabled, these noises don't happen.
Extreme heat soaks can be disabled experimentally by spray cooling pistons to prevent carboned rings.
AM resume...
The crazy HL fan resume spining in the morning regardless of everything being cold.
I believe that's caused by the F-SAM enforcing sleep-mode while HL fans were running... that is a HL firmware bug.
All of this noise is no big deal... What matters is the extreme stored heat that cooks CPS plastics to feed oil-in-harness.
Last edited by CaliBenzDriver; Aug 8, 2025 at 04:20 PM.
Out Of Control!!
Joined: Apr 2019
Posts: 11,923
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
You can easily program these activities with VARIANT coding - The AAC Module has countless great options to tweak your A/C operation. Enjoy customizing improved operation.
MBWorld Fanatic!
Joined: Dec 2011
Posts: 4,372
Likes: 945
W212 FL
I have not taken any attention to this detail , thanks for the heads up
Honestly, I was not aware of the W214s also having humming noises either . I take it as a Mercedes-Benz feature too
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Joined: Oct 2010
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From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
I was always wondering why don’t they make it automatic as it only can do good for the engine and keep cabin cool or warm depending on what the air handling settings are.
“REST” function pumps the engine coolant with a small electric pump after shut to eliminate hot spots in the engine boiling the coolant. It also runs the internal fan at low speed and keeps cabin warmer than it would be without this function or it keeps it cooler until the evaporator coil runs out of cool.
REST works really well for short stops like fueling the car.
