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you can usually get it online cheaper on the stealership website OR cross reference the OEM part number on eBay/Amazon.
My experience with the AAZ warehouse branded item wasn't 100% perfect. And that was while I was installing the new VC. I bought the AAZ oil filter housing. If I have to ever do that again I'm not going to cheap out, I'm going oem.
The aluminum valve cover - it's fckin cool as hell. BUT I had to add 2 washers to the front most bolts on both sides. The plastic PCV pipe and vacuum hose/screw was difficult to line up. The oil dip stick screw is different thread on the aluminum valve cover. The one I received is machine screw threads. So, if you plan to go with the aluminum be prepared for that. Other than that, it's identical and I love it. Definitely cool to do it on the 1st VC change. But, if I ever have to do the VC again I would probably just buy OEM
And I wouldn't suggest buying the AAZ. I'm skeptical.. it might work and you could be fine. But that's just me after my experience I had with the AAZ oil filter housing. The oil cap stem came with a filter attached and was LODGED in there. IThe filter stem separated from the filter cap. had to pull so damn hard to get the stem out. I ended up using the OEM oil filter cap (as I originally planned) but I had a heart attack WTF moment after buttoning up the oil filter housing.
Sorry for the long winded answer. Just want to be transparent and let you know what happened in my experience.
I love the aluminum valve cover but some slight modifications and finagling was needed. I don't believe it is required to fix the problem. I'm absolutely sure a new VC plastic or aluminum will fix the issue. It's all preference.
Great information. I'll probably tackle that job come spring.
The valve cover looks so simple. I'm trying to understand what could be plugged in that system. I'm wondering if a good cleaning (once removed) out of the breather connections in the valve cover (compressed air / suction) might be worth trying. Doesn't look like there's any moving parts in there.
It might be one of those things though that once you get it removed just replace it.
Great information. I'll probably tackle that job come spring.
The valve cover looks so simple. I'm trying to understand what could be plugged in that system. I'm wondering if a good cleaning (once removed) out of the breather connections in the valve cover (compressed air / suction) might be worth trying. Doesn't look like there's any moving parts in there.
It might be one of those things though that once you get it removed just replace it.
Richard
it definitely is simple system. If you look at it, there’s 2 pieces. The Mercedes factory one appears to be RTV’d or glued together. There must be baffles or flaps that get gummed up or worn out. And don’t function as they were brand new.i don’t believe you’ll be able to clean well enough with the size hole there is. (Reference my pic above of the new VC)
in any case, Mercedes should make this a maintenance item. It appears to affect ALOT of c250’s/M271evo’s if not all of them. I agree with you, if it’s off just replace it vs. going through all the trouble trying to clean it.
Even though it wasn’t that hard of a job, I would feel more comfortable with a new one. You do have to pull all the coils, wiring harness, AOS pipe and vacuum line. Plus new gaskets. If your spark plugs are due, it would be a good time to do those and coils. Since you’ll be right there. 🫡
Just change it and be done for another ~100k miles. My older buddy says “I’d rather do it right than over”
Im curious to see what it looks like in there. With the M272 engine the pcv on the passenger side clearly fails by the oil drip pan spinning in the cover and the parts wear down. But the oil separator cover on the drivers side has no moving parts and instead just baffle type things, that I just took apart and cleaned out. Im thinking maybe that hose deteriorates or gets clogged over time. And obviously the gaskets compress and deteriorate.
If theres no moving parts i dont see why it cant be flushed with some type of solvent cleaner.
I was wondering what everyone has the oil level at. With the M272 the manual says to fill it so its between the Min and Max markings. It also says it takes 2 quarts of oil to fill it from Min to the Max lines. So I'm wondering if someone fills it to the Max line does that mean its over filled by 1 quart? When I search for reasons why the cover leaks one of the reasons is the oil level is too high. I'm not meaning the oil level is way over filled, but more like over time its causing the issue.
Im curious to see what it looks like in there. With the M272 engine the pcv on the passenger side clearly fails by the oil drip pan spinning in the cover and the parts wear down. But the oil separator cover on the drivers side has no moving parts and instead just baffle type things, that I just took apart and cleaned out. Im thinking maybe that hose deteriorates or gets clogged over time. And obviously the gaskets compress and deteriorate.
If theres no moving parts i dont see why it cant be flushed with some type of solvent cleaner.
I was wondering what everyone has the oil level at. With the M272 the manual says to fill it so its between the Min and Max markings. It also says it takes 2 quarts of oil to fill it from Min to the Max lines. So I'm wondering if someone fills it to the Max line does that mean its over filled by 1 quart? When I search for reasons why the cover leaks one of the reasons is the oil level is too high. I'm not meaning the oil level is way over filled, but more like over time its causing the issue.
I will be cutting the old valve cover open this weekend to see what’s going on in there.
will upload pics of what I find for everyone to see.
see pics below of the valve cover. I was able to separate it and found that it is 3 separate pieces.
I use a chisel, hammer, and wiz wheel.
the top piece is a cover to the centrifuge and check valve.
the middle piece is an air chamber/passage way. It appeared to be sludged and gummed up. Definitely a failure point. It is causing the check valve to stick under low pressure/low rpm.
It definitely is not all sludge as I used a wiz wheel. But I took my finger and a small pic and was getting sludge and gunk out of the corner of the valve cover.
Great pics. Thanks. I'll definitely think about replacing my wife's valve cover in the spring. That's a fairly closed system. So not sure cleaning it out would be possible.
Great pics. Thanks. I'll definitely think about replacing my wife's valve cover in the spring. That's a fairly closed system. So not sure cleaning it out would be possible.
Richard
Happy to help! My buddy and I were looking at it yesterday and there is absolutely no way to clean all of the air and oil passage ways. Better off putting a new Valve cover on if you're going to tackle this job
Yes, that is exactly what I was experiencing before. The oil cap should not bobble or bounce. It should get sucked into the oil fill by the vacuum. Looks like you need a new valve cover as well!
Reposting from other thread.. this crankcase pressure problem from the oil cap has me puzzled.
I’ve been trying to solve this crankcase pressure problem I’m having. With the car running, when I pull the oil cap off there is (what I believe to be) excessive crank case pressure. I replaced the pcv system hoses and check valve that is located under the intake manifold and that goes into the block of the engine and hooks into the vacuum lines. looking for any other suggestions of what else could be causing this crankcase pressure. Bad EGR? Turbo seals blown? the car runs fine, idle isn’t rough, power is all there. No decrease in fuel economy.
CEL is on for MAP/throttle body sensor positioning. Other than that I’m lost. any help is appreciated!
Anthony
I have had the same issue from valve cover change to valve cover Pcv to Pcv the problem is these engines operate at a slight pressure to keep the pressure on the check valve that is hooked on to the manifold via black tubing after the check valve . So in essence the manifold design doesn’t ensure enough vacuum for the engine layout especially being a turbo model. I would work on keeping your main seals, gaskets and hoses to ensure no oil vapor or leaks
I came across this thread as I too am having this exact issue on a 2013 C250. I recently noticed an oil leak and traced it to the oil filter housing, which I have replaced. In doing that, I noticed that there was, seemingly, excessive oil buildup in the air passages. That led me to looking into the PCV system. As mentioned in this thread, the M271 has two separate PCV systems - referred to as partial load and full load.
Being that there's excessive pressure released through the oil filler cap at idle, my initial thought is that it's the partial load system that has an issue. This is the replacement part for the partial load PCV system. There are two valves, a combination valve that attaches to the engine block (left side in pic) and a check valve (center of pic). I'm not certain what the check valve does, but I know the tube connected to it routes up and to the front of the engine, possibly creating a link to the full load PCV.
Mercedes-Benz Bleed Valve 271-018-09-29
When I had the intake manifold off, I pulled this combination valve out of the engine block and tried to pass air through it. I thought that maybe it might be stuck open, given the oil build up in the intake. In testing, it did not pass air in either direction, which would indicate that it's not stuck open, and may even be stuck closed, but that's hard to confirm without knowing how it's supposed to function. My thought is that there are two possibilities - it's stuck closed, or it only works properly when the other check valve is engaged (i.e. engine is running). Curious if anyone knows.
The OP stated, "I replaced the pcv system hoses and check valve that is located under the intake manifold". If you're still monitoring this thread, do you mean that you replaced this whole assembly in the pic above? And if so, did it make any difference at all? I know that ultimately, replacing the valve cover fixed the issue. So, I'm trying to decide, should I replace just the valve cover or should I also replace this partial load PCV assembly.
I came across this thread as I too am having this exact issue on a 2013 C250. I recently noticed an oil leak and traced it to the oil filter housing, which I have replaced. In doing that, I noticed that there was, seemingly, excessive oil buildup in the air passages. That led me to looking into the PCV system. As mentioned in this thread, the M271 has two separate PCV systems - referred to as partial load and full load.
Being that there's excessive pressure released through the oil filler cap at idle, my initial thought is that it's the partial load system that has an issue. This is the replacement part for the partial load PCV system. There are two valves, a combination valve that attaches to the engine block (left side in pic) and a check valve (center of pic). I'm not certain what the check valve does, but I know the tube connected to it routes up and to the front of the engine, possibly creating a link to the full load PCV.
Mercedes-Benz Bleed Valve 271-018-09-29
When I had the intake manifold off, I pulled this combination valve out of the engine block and tried to pass air through it. I thought that maybe it might be stuck open, given the oil build up in the intake. In testing, it did not pass air in either direction, which would indicate that it's not stuck open, and may even be stuck closed, but that's hard to confirm without knowing how it's supposed to function. My thought is that there are two possibilities - it's stuck closed, or it only works properly when the other check valve is engaged (i.e. engine is running). Curious if anyone knows.
The OP stated, "I replaced the pcv system hoses and check valve that is located under the intake manifold". If you're still monitoring this thread, do you mean that you replaced this whole assembly in the pic above? And if so, did it make any difference at all? I know that ultimately, replacing the valve cover fixed the issue. So, I'm trying to decide, should I replace just the valve cover or should I also replace this partial load PCV assembly.
I have a 2013 C250. I replaced the valve cover and this reduced gas venting through the oil filler considerably, but did not eliminate it. I know this doesn't answer your question but I'm also interested in the answer.
When I had the intake manifold off, I pulled this combination valve out of the engine block and tried to pass air through it. I thought that maybe it might be stuck open, given the oil build up in the intake. In testing, it did not pass air in either direction, which would indicate that it's not stuck open, and may even be stuck closed, but that's hard to confirm without knowing how it's supposed to function. My thought is that there are two possibilities - it's stuck closed, or it only works properly when the other check valve is engaged (i.e. engine is running). Curious if anyone knows.
Here's a video of the complete oil filter housing replacement that includes the PCV test I mentioned.
35:02 Partial Load PCV valve testing
58:52 Crankcase pressure demonstration
*EDIT: Check the comments of my video. There's a link to a Russian video (dubbed to English) that goes deep into how the Partial Load PCV valve works and ways to fix it. Based on what he's saying it looks like my valve is not working as it should and needs to be replaced/fixed.
Last edited by cmcfarling09@li; Jan 28, 2026 at 11:09 PM.
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.
Engine bay upgrade- w204 c250
