Hello fellow W211 E55 enthusiasts!

Another issue with my E55. A few weeks ago after starting a car I've noticed a strange noise, kind of like grinding or screeching (not sure how to describe it) coming from the front of the car. It happens occasionally, not with every start. Also noticed that it happenes when engine is already warm. This week, after driving a short distance, enough to get the engine to the fully operational temperature, car set for about an hour before I started it again. This time when I started the car, the noise happened following by a white smoke coming from under the hood on the drivers side. I have killed the car and popped the hood. There was a burned electrical smell. Removed plastic fuse cover in hopes to find the source of smoke. No luck! Came back an hour later for a closer look, in hopes that another person could listen under the hood as I crank the car a few times. Nothing! No noise, no smoke, no smell. No lights on the dash. Scanner didn't show anything. Although, I don't really know which module to look at.

Forward two days–no problems. Every time I star the car, I listen intently for the noise. Nothing from a cold start. But when I started the car again on a fully warm engine, I've heard the noise followed by electrical burning smell, but no smoke. Thankfully, drive home was less than a mile. Parked, looked under the hood for any spills of fluids, wet spots, melted wires... Nothing!

I will mention that the car does have a slow oil leak what seems to be from the oil drain plug. Scanned the forums for any information that could point to the causes, but no luck.Any of you experience anything like this? Suggestions, beside going to the dealer.

The link is from my original post in W211 forum.
https://mbworld.org/forums/e-class-w211/871416-strange-noise-burning-electric-smell-smoke.html

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Update: 2 weeks without any noices. Today temperature outside was 105°f, plus whatever heat from the engine bay added to it. Actually had a chance to get a short video of the problem with help from my mom. Although she got spooked by the smoke.
By the looks of it, mp4 video format is not supported. So I've attached a couple of screenshots.

First picture has arrows pointing to the area where the smoke/mist comes from. I say mist because when it happens, it is almost like a shot of NOS. Which leads me to believe that whatever is the cause it is under pressure.


In the picture above you can see steam/smoke coming from under the coolant reservoir area (top left corner of the picture).

Hoping this might give someone an idea of what might be the cause of this.

 

It's hard to tell but my guess would be your coolant reservoir is leaking and spraying hot coolant. These get old and leak and need to be replaced.

https://eeuroparts.com/product/mahle/CRT202000S

 

In that area you also have the EVAP solenoid. its connected via a hardpipe to the back of the supercharger

 

From a video, it does look like it's spraying a fine mist. Not really smoke.

 

Evap for the fuel system, right?
Sorry, a newbie when it comes to engines, but wouldn't it throw a code or an engine light?

 

Yeah correct, not a high chance that might be your "smoking" gun (pun intended). I only mentioned it, as that system/part is in that area.

Might be a good idea to do a leak test on the cooling circuit, maybe the intercooler or radiator has a tiny leak which only appears when there is pressure on the system (you mentioned it happens when the engine is warm)

 

Have not done any further testing, but since my previous post, problem didn't come up again.
With this car, if it is not one thing, it's another. 😔