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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!
It's definitely not normal crankcase pressure. I'll record and post a video of what I'm experiencing.
CEL is unrelated. Code (p0068) MAP/MAF throttle position correlation. It didn't come on until after I took it to my car to the local Mercedes dealership to see if they could figure out what was causing the crankcase pressure and they told me I have a cracked intake manifold. Wanted to charge me $1800 for a new manifold and labor. CEL was not on until after Mercedes was messing around with my car and did a smoke test on it.
I told them their diagnosis didn't make any sense because if I had a crack or leak on the intake side, the car would be miss firing running like crap and not building boost.
I've replaced the boost sensor and air intake temp sensors so far. I will be replacing the 2 MAP sensors next when I do my oil filter housing as that is currently leaking and blowing oil out from the excess pressure.
I also did all new intake manifold gaskets when I replaced the PVC that's located under the intake manifold and inspected the manifold while I had it out.
Appreciate the feedback I'll post a video shortly.
Forgot to mention, I went to a used car dealership to see if the cars for sale had the positive crankcase pressure issue and they did.
I checked out a 2014 c250 sedan and a 2015 slk250. They both had the positive crankcase pressure coming from the cap.
if anyone else could test this out or knows the fix please advise. I’ve already replaced the PCV that is underneath the intake manifold that runs into the block.
After looking up the service manual online and studying the engine last night I believe I've found the reason behind the crankcase pressure issue im experiencing.
The m271 evo engine has 2 PCV systems. Low pressure PCV (vacuum/suction lines that run under the intake manifold) and high pressure PCV (cyclone centrifuge located inside the valve cover)
while doing more testing last night, I pulled the oil cap off and rested it on the oil fill. It was popping up and jumping around but would settle for a second or two then would go back to jumping. I then reved the car and it got sucked in while under load.
My theory - the High pressure PCV located in the valve cover is not working as it should at low pressure (idle) therefor creating the crankcase pressure.
I've ordered a new aluminum valve cover and will report back if that fixes my crankcase pressure issue at idle.
Interesting. I wonder how that Double Cyclone Oil Separator works and how it would fail? Took me awhile to comprehend how my M272 oil separators work. The low side cover is just a series of tabs that must collect oil vapor and it falls down into the cover. The high side seems to collect the oil by spinning and collecting oil on the outside. Made me realize the low side should only ever need to be cleaned and not replaced, no moving parts. Except for a worn gasket. The high side is always spinning and the seal will get worn over time and always need to be replaced at some point.
Would be interesting to see whats inside the valve cover. I looked around online but could not find any info. When you get the new cover take the old one apart and see what it looks like in there, see what has failed.
Interesting. I wonder how that Double Cyclone Oil Separator works and how it would fail? Took me awhile to comprehend how my M272 oil separators work. The low side cover is just a series of tabs that must collect oil vapor and it falls down into the cover. The high side seems to collect the oil by spinning and collecting oil on the outside. Made me realize the low side should only ever need to be cleaned and not replaced, no moving parts. Except for a worn gasket. The high side is always spinning and the seal will get worn over time and always need to be replaced at some point.
Would be interesting to see whats inside the valve cover. I looked around online but could not find any info. When you get the new cover take the old one apart and see what it looks like in there, see what has failed.
@TimC300 definitely will be separating the original valve cover if the new one works.
That's what my buddy and I were thinking also. Something must be worn/broke in the high pressure PCV located in the valve cover.
Will post updates when I swap out the valve cover.
Hey ant did you try to unscrew the PCV line coming out of the VC to see if there's any suction there? If there is then it would mean the PCV system is working correctly and the VC is clogged.
Hey ant did you try to unscrew the PCV line coming out of the VC to see if there's any suction there? If there is then it would mean the PCV system is working correctly and the VC is clogged.
Hey @AJ88 , are you referring to the big plastic AOS pipe that runs from the valve cover to the intake? Or the little vacuum line that is screwed into the AOS pipe top screw, that runs to the low side PCV?
My issue is at idle, the PCV in the VC definitely works when it's under load. Just not at idle.
I am hesitant to loosen the plastic AOS pipe that comes out of the valve cover down to the intake. because I cracked the coolant pipe that runs right below it. As they are connected from factory. Cracked it while I was installing a new air intake.
have you tried that test and removed the AOS pipe?
Hey @AJ88 , are you referring to the big plastic AOS pipe that runs from the valve cover to the intake? Or the little vacuum line that is screwed into the AOS pipe top screw, that runs to the low side PCV?
My issue is at idle, the PCV in the VC definitely works when it's under load. Just not at idle.
I am hesitant to loosen the plastic AOS pipe that comes out of the valve cover down to the intake. because I cracked the coolant pipe that runs right below it. As they are connected from factory. Cracked it while I was installing a new air intake.
have you tried that test and removed the AOS pipe?
Ant
I was thinking the small one going down which I assume is the low pressure. Its just the one long torx screw.
I was thinking the small one going down which I assume is the low pressure. Its just the one long torx screw.
GOtchya, yes I have pulled that line off with the log torx screw.
ITs connected to the low pressure PCV like you said. New valve cover says it should be delivered Friday this week. Will be doing the install this upcoming weekend.
I will let you know how the valve cover comes out tomorrow @Richard Koop !
I installed a new oil filter housing and gasket today. Did not get to the valve cover due to cracked intake manifold gaskets and finagling with the oil filter housing/starter etc.
i will be doing the new valve cover today (Sunday) when I get the new intake manifold gasket and button up that job.
i will be uploading a video with commentary on the entire job to YouTube when I’m all wrapped up.
here’s some pics of the new aluminum valve cover I will be installing.
Nice looking valve cover. Great to see people sharing their work on these forums. Very much appreciated by others like me.
My other vehicles are Honda/Toyota/Infiniti which there is a wealth of information out there. Mercedes I find things difficult to find. Had to get my head wrapped around the body style and engine number system. My wife's is a 2012 Mercedes C250 coupe 1.8L turbo but when you go searching you have to search on like W204 body style and engine M271.860..
Nice looking valve cover. Great to see people sharing their work on these forums. Very much appreciated by others like me.
My other vehicles are Honda/Toyota/Infiniti which there is a wealth of information out there. Mercedes I find things difficult to find. Had to get my head wrapped around the body style and engine number system. My wife's is a 2012 Mercedes C250 coupe 1.8L turbo but when you go searching you have to search on like W204 body style and engine M271.860..
Richard
I Agree. the w204 c250 m271 evo - what your wife and I have, there is not much information on this particular engine. Alot of w204 owners went with the V6 or V8 models. (C300,c350,c63)
Happy to share the information because I wasn't able to find it either! I'm glad a handful of people are interested in the job and keeping this thread going.
Intake manifold gaskets come in today at 130. I should have an update by this evening to the thread on whether or not the new VC worked.
I have successfully installed the new VC an can chalk it up as a success
my car no longer bobbles and blows the oil fill cap all over the place while resting over the fill hole at idle.
it has its suction (vacuum) back at idle and pulls the cap into the fill hole as it should.
Low rpm/slow driving seems much smoother now. Take off and accelerate are much smoother also. This is just from the ride home first impressions.
I would say if you are suffering from multiple oil leaks and are suffering from any or all of the symptoms I’ve listed above, you SHOULD REPLACE YOUR ENTIRE VALVE COVER.
here are a few pics of the valve cover off and the new one on. Will post videos shortly. I am going to monitor oil levels and look for leaks. But I am 100% sure this was the solution.
12-24-2023, 08:39 AM
Update
Great to see people sharing their work on these forums. Very much appreciated by others like me.
