S-Class (W221) 2007-2013: S 320 CDI, S 350, S 450, S 500, S 550, S 420 CDI, S 600

Strangest Oil Leak Ever

Old Jun 11, 2025 | 05:13 PM
  #1  
rafaelq's Avatar
Thread Starter
Newbie
 
Joined: Jun 2025
Posts: 2
Likes: 0
Angry Strangest Oil Leak Ever

Greetings All,

I'm experiencing the strangest oil leak I've ever encountered with my W221 - 2012 S 550. It has the M278.932 engine in it. I've replaced the sealant (RTV) on the valve covers and it continues to leak. The leak is occurring on the driver side near the coil/sparkplug nearest to the firewall. Just above the heat shield that covers the exhaust manifold, the oil is pooling on that heat shield, then dripping off onto the exhaust manifold and burning off. There is no oil pooling in that sparkplug well. There is NO visible damage to the block itself, we've inspected everything as I currently have the complete drive-train out of my S 550. I just can't seem to find where the oil is coming from. It only leaks while it's running. Has anyone ever seen this before? I'm at the end of my rope here. Thanks in advance!
Reply
Old Jun 11, 2025 | 05:34 PM
  #2  
ChrisHimself's Avatar
SPONSOR
Photogenic
Liked
Loved
Community Favorite
 
Joined: Apr 2021
Posts: 846
Likes: 559
From: San Jose, CA
11 E550, 16 AMG GTS, 13 S550
its not the front timing cover at the top? thats the most common leak and its a known defective RTV seal from the factory. The finish prevents good RTV adhesion
__________________
Alpha European Autotech
Purchase Amsoil at 25% off from me

Chris Tran, Retired Alpha European Autotech Owner
Amsoil Independent Dealer #7236674
Reply
Old Jun 11, 2025 | 05:35 PM
  #3  
rafaelq's Avatar
Thread Starter
Newbie
 
Joined: Jun 2025
Posts: 2
Likes: 0
Not that I can see thus far, we've crawled this thing and just can't figure it out
Reply
Old Jan 14, 2026 | 10:50 AM
  #4  
Papushkian's Avatar
Junior Member
5 Year Member
 
Joined: Oct 2016
Posts: 46
Likes: 8
2009 S450, 2011 GL450, 2008 C300 Sport
Originally Posted by rafaelq
Not that I can see thus far, we've crawled this thing and just can't figure it out
Did you figure it out?
Reply
Old Jan 14, 2026 | 07:19 PM
  #5  
Alexie's Avatar
Super Member
Photoriffic
Shutterbug
Community Builder
Community Influencer
 
Joined: Jun 2025
Posts: 784
Likes: 249
From: USA
Originally Posted by rafaelq
Greetings All,

I'm experiencing the strangest oil leak I've ever encountered with my W221 - 2012 S 550. It has the M278.932 engine in it. I've replaced the sealant (RTV) on the valve covers and it continues to leak. The leak is occurring on the driver side near the coil/sparkplug nearest to the firewall. Just above the heat shield that covers the exhaust manifold, the oil is pooling on that heat shield, then dripping off onto the exhaust manifold and burning off. There is no oil pooling in that sparkplug well. There is NO visible damage to the block itself, we've inspected everything as I currently have the complete drive-train out of my S 550. I just can't seem to find where the oil is coming from. It only leaks while it's running. Has anyone ever seen this before? I'm at the end of my rope here. Thanks in advance!
Check the camshaft solenoid seal directly above that area. Common on the M278. They leak while running and oil runs down the back of the head, pooling on the heat shield. Valve cover gasket itself can also seep from the very back corner. Since it's out, clean it bone dry, start it, and watch that solenoid.
Reply
Old Jan 15, 2026 | 12:31 AM
  #6  
Max Blast's Avatar
MBWorld Fanatic!
15 Year Member
Photogenic
Loved
Community Favorite
 
Joined: Jan 2010
Posts: 3,120
Likes: 784
NGL450 w/EORP, S550
If you remove the fake firewall, you’ll see it
Reply

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 

Thread Tools
Search this Thread
Rate This Thread
Rate This Thread:
You have already rated this thread Rating: Thread Rating: 0 votes,  average.


All times are GMT -4. The time now is 04:44 PM.

story-0
New Electric Mercedes-AMG GT 4-Door Coupe Unveiled: 10 Things You Need to Know

Slideshow: Mercedes-AMG's new electric GT 4-Door Coupe trades combustion for software, synthetic noise, and more than 1,100 horsepower.

By Verdad Gallardo | 2026-05-20 20:08:15


VIEW MORE
story-1
6 Mercedes Models That Did NOT Age Well (But Are Somehow Still Cool)

Slideshow: Not every Mercedes design becomes timeless, some feel stuck in the era they came from.

By Verdad Gallardo | 2026-05-12 18:09:07


VIEW MORE
story-2
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun

Slideshow: Yes, Mercedes built manual cars, and some of them are far more interesting than you'd expect.

By Verdad Gallardo | 2026-05-02 12:36:58


VIEW MORE
story-3
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren

Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.

By Verdad Gallardo | 2026-04-29 11:19:28


VIEW MORE
story-4
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine

Slideshow: Before curves took over, Mercedes mastered the art of the straight line, and some of those shapes still look right today.

By Verdad Gallardo | 2026-04-25 12:05:49


VIEW MORE
story-5
Flawlessly Restored Mercedes 190E Evo II Heads to Auction

Slideshow: The 190E Evolution II shows how a homologation necessity became a six-figure collector icon.

By Verdad Gallardo | 2026-04-22 17:53:47


VIEW MORE
story-6
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know

Slideshow: Mercedes is turning one of its core nameplates electric, and the details show just how serious this shift is.

By Verdad Gallardo | 2026-04-21 13:58:06


VIEW MORE
story-7
Mercedes EQS Gets A Major Update: Everything You Need to Know

Slideshow: Faster charging, longer range, and a controversial steer-by-wire system define the latest evolution of Mercedes-Benz EQS.

By Verdad Gallardo | 2026-04-15 10:35:34


VIEW MORE
story-8
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve

Slideshow: These overlooked Mercedes-Benz models never got the spotlight, but they quietly delivered more than most remember.

By Verdad Gallardo | 2026-04-13 19:35:45


VIEW MORE
story-9
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping

Slideshow: A well-used 1991 Mercedes-Benz 300D with more than one million miles is now looking for a new owner, and it still appears ready for more.

By Verdad Gallardo | 2026-04-10 10:05:15


VIEW MORE