RMS Fail Club
Out Of Control!!
Joined: Sep 2018
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From: unbegrenzt
2017 GLE350 4MATIC
For those that are curious about the OVS, I created a video on YT that looks at how they work and what a failed one looks like.
https://youtu.be/HC4UKDlof2U?si=a35qrnKBAP1asxPc
https://youtu.be/HC4UKDlof2U?si=a35qrnKBAP1asxPc
Did you apply (human lungs) vacuum or pressure to each of the ports? There should be check valves in some or all of them. These can become blocked.
I did’t get your point regarding multiple mentions of crankcase vacuum. What prompted the comments?
MBWorld Fanatic!
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From: Newcastle, WA
2019 S63 4Matic+, 2018 E400 Cabrio, wardens car.
Thanks Chassis, I did not apply any mechanical or human vacuum to any of the ports as there were no check valves in the port areas that I recall. The only check valve I found was the one that was orange in color and appeared to be sticky upon mechanical manipulation. On the vacuum, I have heard several comments about OVS units causing crankcase pressure issues. Mine was not positive pressure but rather negative pressure or vacuum. I think that this is a vacuum issue, and not a situation of crankcase over pressurization. While it may be anecdotal, there was a substantial difference in vacuum pressure when removing the oil fill cap pre OVS replacement and post replacement. That tells me that too much vacuum can cause seals to be sucked inward and then leak.
Out Of Control!!
Joined: Sep 2018
Posts: 14,678
Likes: 4,578
From: unbegrenzt
2017 GLE350 4MATIC
Significant crankcase vacuum at idle is normal with modern German engines. Porsche/VAG specify 150mbar vacuum at idle for the EA825 4.0TTV8 and EA839 3.0T/2.9TTV6 engines. This feels like quite a large amount of suction when removing the oil fill cap at idle. A rennlist user measured crankcase vacuum and the result was very close to 150mbar and within expected ranges of operating conditions and measurement variation.
Has anyone posted the specified normal MB crankcase vacuum at idle for the M17x? It is likely to be close to 150mbar. All the German engineers attend the same technical conferences and graduated from a small list of German universities.
In other words, the engineering gene pool is shallow. VAG hasn't discovered any new laws of physics that MB and BMW don't already know about.
The main AI chatbots say normal crankcase vacuum should be 10mbar-50mbar at idle. I am not convinced. AI is often wrong. I told Grok it was factually incorrect the other day and it agreed with me.
Has anyone posted the specified normal MB crankcase vacuum at idle for the M17x? It is likely to be close to 150mbar. All the German engineers attend the same technical conferences and graduated from a small list of German universities.
In other words, the engineering gene pool is shallow. VAG hasn't discovered any new laws of physics that MB and BMW don't already know about.
The main AI chatbots say normal crankcase vacuum should be 10mbar-50mbar at idle. I am not convinced. AI is often wrong. I told Grok it was factually incorrect the other day and it agreed with me.
Last edited by chassis; Mar 11, 2026 at 03:49 PM.
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From: Pacific Northwest
2001 S600 V12 Sold, 2011 Jaguar XFR Sold, 2017 S550 4-Matic, 2018 S63 AMG Sedan
Thanks Chassis, I did not apply any mechanical or human vacuum to any of the ports as there were no check valves in the port areas that I recall. The only check valve I found was the one that was orange in color and appeared to be sticky upon mechanical manipulation. On the vacuum, I have heard several comments about OVS units causing crankcase pressure issues. Mine was not positive pressure but rather negative pressure or vacuum. I think that this is a vacuum issue, and not a situation of crankcase over pressurization. While it may be anecdotal, there was a substantial difference in vacuum pressure when removing the oil fill cap pre OVS replacement and post replacement. That tells me that too much vacuum can cause seals to be sucked inward and then leak.
Significant crankcase vacuum at idle is normal with modern German engines. Porsche/VAG specify 150mbar vacuum at idle for the EA825 4.0TTV8 and EA839 3.0T/2.9TTV6 engines. This feels like quite a large amount of suction when removing the oil fill cap at idle. A rennlist user measured crankcase vacuum and the result was very close to 150mbar and within expected ranges of operating conditions and measurement variation.
Has anyone posted the specified normal MB crankcase vacuum at idle for the M17x? It is likely to be close to 150mbar. All the German engineers attend the same technical conferences and graduated from a small list of German universities.
In other words, the engineering gene pool is shallow. VAG hasn't discovered any new laws of physics that MB and BMW don't already know about.
The main AI chatbots say normal crankcase vacuum should be 10mbar-50mbar at idle. I am not convinced. AI is often wrong. I told Grok it was factually incorrect the other day and it agreed with me.
Has anyone posted the specified normal MB crankcase vacuum at idle for the M17x? It is likely to be close to 150mbar. All the German engineers attend the same technical conferences and graduated from a small list of German universities.
In other words, the engineering gene pool is shallow. VAG hasn't discovered any new laws of physics that MB and BMW don't already know about.
The main AI chatbots say normal crankcase vacuum should be 10mbar-50mbar at idle. I am not convinced. AI is often wrong. I told Grok it was factually incorrect the other day and it agreed with me.
MBWorld Fanatic!
Joined: Aug 2007
Posts: 1,830
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From: Pacific Northwest
2001 S600 V12 Sold, 2011 Jaguar XFR Sold, 2017 S550 4-Matic, 2018 S63 AMG Sedan
Thanks Chassis, I did not apply any mechanical or human vacuum to any of the ports as there were no check valves in the port areas that I recall. The only check valve I found was the one that was orange in color and appeared to be sticky upon mechanical manipulation. On the vacuum, I have heard several comments about OVS units causing crankcase pressure issues. Mine was not positive pressure but rather negative pressure or vacuum. I think that this is a vacuum issue, and not a situation of crankcase over pressurization. While it may be anecdotal, there was a substantial difference in vacuum pressure when removing the oil fill cap pre OVS replacement and post replacement. That tells me that too much vacuum can cause seals to be sucked inward and then leak.
It looks like there are 2 inlets from the crankcase, one lower an one upper. Then there's the return for the vapor into the intake, and an oil return line to the lower crankcase. I've looked at YT videos for the design of other oil separators, I bet you wouldn't be surprised to know that these are far more complicated than others. It's just a basic "catch-can" but MB had to make them both complicated and non-servicable.
My goal would be able to figure out a way to snake a line inside the OVS to release the valve from the stuck position.
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Member
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honestly gotta say, my 2022 GLE63 AMG had issues with the remote start module too after a software update, so I feel your pain. Not exactly sure what's going on but hopefully someone from MBUSA or a tech-savvy forum member can shed some light on it.
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From: Newcastle, WA
2019 S63 4Matic+, 2018 E400 Cabrio, wardens car.
@carlosinseattle Unfortunately I tossed them once I was done cutting them up and doing the video as it was an oily mess. After talking to my mechanic though I do wonder if it is something you could DIY. It doesn't sound like any special tools are required and it is just time consuming to take everything apart and then put it back together. Book time is 6 hours and he said that is about what it took. Parts are around 500 for both sides. I might have done mine myself if not for the warranty. Regardless I would just get the new units installed and be done with it, especially if you are out of warranty as the RMS and Valve Cover Gaskets are very spendy to fix.
Out Of Control!!
Joined: Sep 2018
Posts: 14,678
Likes: 4,578
From: unbegrenzt
2017 GLE350 4MATIC
In fact, pressure inside the crankcase is vacuum, i.e. below atmospheric.
In fact, two return paths exist between OVS and crankcase: one path for unboosted induction (e.g. idle) and one path for boosted induction.
Zero doubt exists about the above two statements.
In fact, two return paths exist between OVS and crankcase: one path for unboosted induction (e.g. idle) and one path for boosted induction.
Zero doubt exists about the above two statements.
MBWorld Fanatic!
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From: Pacific Northwest
2001 S600 V12 Sold, 2011 Jaguar XFR Sold, 2017 S550 4-Matic, 2018 S63 AMG Sedan
For the path that returns the separated oil from the OVS back to the crankcase, does it only return oil when the car is off and there's no vacuum at all. Or is the oil in the return pathway drawn back into the engine by vacuum?
MBWorld Fanatic!
Joined: Aug 2007
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From: Pacific Northwest
2001 S600 V12 Sold, 2011 Jaguar XFR Sold, 2017 S550 4-Matic, 2018 S63 AMG Sedan
@carlosinseattle Unfortunately I tossed them once I was done cutting them up and doing the video as it was an oily mess. After talking to my mechanic though I do wonder if it is something you could DIY. It doesn't sound like any special tools are required and it is just time consuming to take everything apart and then put it back together. Book time is 6 hours and he said that is about what it took. Parts are around 500 for both sides. I might have done mine myself if not for the warranty. Regardless I would just get the new units installed and be done with it, especially if you are out of warranty as the RMS and Valve Cover Gaskets are very spendy to fix.
Senior Member
Joined: Dec 2025
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From: Keep it simple - keep it OEM
AMG C63s Coupe
For those that are curious about the OVS, I created a video on YT that looks at how they work and what a failed one looks like.
https://youtu.be/HC4UKDlof2U?si=a35qrnKBAP1asxPc
https://youtu.be/HC4UKDlof2U?si=a35qrnKBAP1asxPc
check & clear situation like a swat team it does
no bla bla but fundamental fakts.
i like that - THX
There is a updated oem part number for this parts (if its same as C63s) double check DIY by vin & mb parts guy!
This spring with lid is stuck in pipe as it appears in video.
Vacuum vs Overpessure - have you checked this for sure what is it exactly of them ?
I dont think that vacuum push oil through
seals (as known on mosty LS2) thats physical not possible.
I dont think that it was bad constructed … maybe heat and / or chemical substances from engine oil made this jam by time (material change)
on these little smal parts mechanism inside.
(First i was thinking in theory some filter / camber inside of the part is clogged by using bad worn engine oil over time etc. (and than overpressure makes all that oil leaks on M177 mostly LS2))
If you bored - buy oem updated part # and do it again.
There are some things i do to keep my high end german engenerd & build AMG healthy :
- i dont abuse it (no chip tuning etc)
- use MB OEM parts
- service as MB Service Manual says (M177 LS*)
- use high quality oil etc as told by MB specification www MB operating fluids
- daily some good words to my AMG
Last edited by C63s_Jack; Mar 14, 2026 at 07:27 AM.
Out Of Control!!
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From: unbegrenzt
2017 GLE350 4MATIC
There are almost assuredly check valves in the lines between the OVS and the induction system. This is not the spring and diaphragm. Anything that becomes tainted with crankcase gases will eventually sludge and become blocked.
Last edited by chassis; Mar 14, 2026 at 11:37 AM.
Senior Member
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From: Keep it simple - keep it OEM
AMG C63s Coupe
That only check valve is that shown in video from OVS system.
if a oem part gets a update with new part# so i think it had a problem.
Last edited by C63s_Jack; Mar 14, 2026 at 12:59 PM.
Out Of Control!!
Joined: Sep 2018
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From: unbegrenzt
2017 GLE350 4MATIC
The complete PCV and OVS diagram needs to be added to this thread. I don’t have the diagram. Check valves may not be physically integrated into the OVS component and rather installed elsewhere. Check valves are in the system and can cause problems if they fail/become blocked.
A good time to remind readers that OVSs are nothing more than factory catch cans with an automatic drain feature.
A good time to remind readers that OVSs are nothing more than factory catch cans with an automatic drain feature.
Last edited by chassis; Mar 15, 2026 at 06:43 PM.
Senior Member
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Posts: 425
Likes: 37
From: Keep it simple - keep it OEM
AMG C63s Coupe
Out Of Control!!
Joined: Sep 2018
Posts: 14,678
Likes: 4,578
From: unbegrenzt
2017 GLE350 4MATIC
The video posted upthread, as good as it is, leaves important questions unanswered.
@superpop if the parts are still around, it would be helpful if you can apply human pressure and vacuum to each of the 5 ports on the OVS. Because the OVS is dissected, this human pressure/vacuum test isolates each port to test for the presence and function of a check valve.
The spring-and-plunger component is a pressure control device that regulates pressure on the crankcase side of the OVS. BMW and VAG/Porsche use a polymer membrane in this location. Remember, all German automotive engineers went to a small number of universities, consult with the same small number of specialists (FEV and AVL), and go to the same small number of technical conferences. The engineering gene pool is shallow and there is nothing new under the sun.
Two orange ports in particular are of interest - they appear to have fully closed orange membranes. But it is not possible that they are fully closed because they are clearly openings between the engine and the OVS. So a means of passing vapor must be present.
The smallest diameter port is also of interest and is adjacent to the orange port which is clearly open and without an orange membrane covering it.
Lastly is the appendage below the turbo inlet adapter. This is the sixth position which is a candidate for a check valve. Human vacuum and pressure needs to be applied to the tube that connects the OVS with the turbo inlet adapter.
After the human vacuum/pressure test, it would super cool to see each of the five ports on the OVS sectioned (cut) along the flow axes.
@superpop if the parts are still around, it would be helpful if you can apply human pressure and vacuum to each of the 5 ports on the OVS. Because the OVS is dissected, this human pressure/vacuum test isolates each port to test for the presence and function of a check valve.
The spring-and-plunger component is a pressure control device that regulates pressure on the crankcase side of the OVS. BMW and VAG/Porsche use a polymer membrane in this location. Remember, all German automotive engineers went to a small number of universities, consult with the same small number of specialists (FEV and AVL), and go to the same small number of technical conferences. The engineering gene pool is shallow and there is nothing new under the sun.
Two orange ports in particular are of interest - they appear to have fully closed orange membranes. But it is not possible that they are fully closed because they are clearly openings between the engine and the OVS. So a means of passing vapor must be present.
The smallest diameter port is also of interest and is adjacent to the orange port which is clearly open and without an orange membrane covering it.
Lastly is the appendage below the turbo inlet adapter. This is the sixth position which is a candidate for a check valve. Human vacuum and pressure needs to be applied to the tube that connects the OVS with the turbo inlet adapter.
After the human vacuum/pressure test, it would super cool to see each of the five ports on the OVS sectioned (cut) along the flow axes.
Last edited by chassis; Mar 20, 2026 at 11:18 AM.
Junior Member
Joined: Oct 2021
Posts: 26
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From: NYC
W213 E63S
2018 E63. RMS failed (the first time) August 2024 when the car had ~43,000 miles. Car was garage kept year round and only driven between spring and fall. Despite staying on top of regular maintenance, the RMS failed a second time during fall 2025 and less than 10,000 miles later.
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From: Newcastle, WA
2019 S63 4Matic+, 2018 E400 Cabrio, wardens car.
2018 E63. RMS failed (the first time) August 2024 when the car had ~43,000 miles. Car was garage kept year round and only driven between spring and fall. Despite staying on top of regular maintenance, the RMS failed a second time during fall 2025 and less than 10,000 miles later.
Junior Member
Joined: Oct 2021
Posts: 26
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From: NYC
W213 E63S
Inconclusive if that would’ve prevented the issue, but I’ve since parted ways with the car.
MBWorld Fanatic!
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From: Newcastle, WA
2019 S63 4Matic+, 2018 E400 Cabrio, wardens car.
Ya, I had the same fight with them over OVS. Really stupid as they had to pay to replace them for me a few months ago when my Vacuum was through the roof. You sometimes feel like a hostage negotiator with Fidelity and MB.
MBWorld Fanatic!
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Posts: 1,830
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From: Pacific Northwest
2001 S600 V12 Sold, 2011 Jaguar XFR Sold, 2017 S550 4-Matic, 2018 S63 AMG Sedan
2018 E63. RMS failed (the first time) August 2024 when the car had ~43,000 miles. Car was garage kept year round and only driven between spring and fall. Despite staying on top of regular maintenance, the RMS failed a second time during fall 2025 and less than 10,000 miles later.
If you had a failed RMS, cut and paste the following and post your pertinent details to add to the database of affected vehicles:
Year: 2019
Model: E63S
RMS Failure Mileage: 38K miles
Style/Frequency of Driving: weekend/spirited
Original Owner: No
Failed Before or After Warranty: After
Has it re-leaked after repair: no
Cost to repair: $5700 (warranty vs OOP)
Who repaired it: Indy vs dealership
For those who are new to the RMS/OVS issue, see this sticky for numerous links of discussions regarding the issue, new part numbers, theories on causes of the failures, posted repair bills, how warranty coverage can help
https://mbworld.org/forums/w213-amg/...fixes-diy.html
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2001 E55AMG
Also, NY dealer labor hours, part costs, and per hour labor rates billed are just crazy sometimes. I'd suggest customers go visit Chris at Benzel Busch Mercedes-Benz in Englewood, New Jersey.
Trenton O. Gibson
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