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My 2012 C250 valve cover has been leaking even after changing the gasket. I couldn't find any cracks but I noticed a small gap at the rear right of the valve cover and was wondering if i could somehow tap that back in with a rubber mallet. My concern is if beating on it would somehow mess up the gasket and make it worse. I checked used VCs on ebay and almost all of them have some sort of separation at the rear of the VC so if I were to replace it would probably have to be original new. What do you guys think??
Last edited by AJ88; Dec 26, 2023 at 07:15 PM.
Reason: update
Im not familiar with that engine but im wondering would oil even be able to leak out that joint? I looked on ebay to see what they look like and to me it looks like the oil doesn't reach that area. Unless im totally wrong. which i probably am.
Im not familiar with that engine but im wondering would oil even be able to leak out that joint? I looked on ebay to see what they look like and to me it looks like the oil doesn't reach that area. Unless im totally wrong. which i probably am.
Hey Man,
I've been doing research on the PVC system on these cars. What you're looking at is the high pressure PCV. Its built into the valve cover. I am having excessive crankcase pressure at idle and also losing oil out of my valve cover and other seals. Due to the crankcase pressure at idle blowing the oil out of the seals.
My theory, the only way to fix it is replacing the entire valve cover and you will get a new high pressure PCV. You can't just replace the valve cover gasket.
Test your car running at idle, pull the oil cap and see if you have excessive crankcase pressure coming out.
Then place the oil cap back on the oil fill but DO NOT tighten. Let it sit in place. Have someone rev it and see if it gets sucked in (vacuum).
I've ordered a new aluminum valve cover and will report back if that fixes my problem. I already replaced the low pressure PCV that's located under the intake manifold and that drains into the block near the driver side motor mount.
My 2012 C250 valve cover has been leaking even after changing the gasket. I couldn't find any cracks but I noticed a small gap at the rear right of the valve cover and was wondering if i could somehow tap that back in with a rubber mallet. My concern is if beating on it would somehow mess up the gasket and make it worse. I checked used VCs on ebay and almost all of them have some sort of separation at the rear of the VC so if I were to replace it would probably have to be original new. What do you guys think??
I see that now. Looking at other photos I see a connection for a hose. If the cover is open I'm guessing a new one is the way to go.
Yes, that hole you see is for the AOS (air oil separator) pipe. It acts as a suction line to the air intake tube connected to the turbo. Which sucks the crankcase air out and through the turbo.
The oil like you said in the other thread, is spun out on the walls of the valve cover and flows back down into the engine.
After doing a lot of research on YouTube, other manufacturers do this as well. Where the PCV is located in the valve cover.
Im curious to see what it looks like under there for #4. Are there moving parts or is it just baffles?
I can see where the oil vapor leaves from the underside of the cover, #1 in the diagram.
The spinning type oil separator (oil drip pan) is mounted to the cam shaft on mine, spins accordingly. I found an interesting diagram showing its basic function.
Im curious to see what it looks like under there for #4. Are there moving parts or is it just baffles?
I can see where the oil vapor leaves from the underside of the cover, #1 in the diagram.
The spinning type oil separator (oil drip pan) is mounted to the cam shaft on mine, spins accordingly. I found an interesting diagram showing its basic function.
So where you circled in the pics above are actually on opposite sides! My buddy and I had to take another look at it as well because we thought the same thing.
The diagram style pic from the service manual is showing you the exterior of the valve cover. The picture of the real thing is flipped and you're looking at the inside of the valve cover.
The baffles or valves or whatever the PCV is made up of is on the sealed side (same side as the oil cap)
Definitely curious how it works, if the new valve cover fixes my issue I already planned to tear the old one apart lol
Appreciate the feedback but I am already aware of the PCV routing in the VC. My question is if it would be a wise idea to try to tap the upper VC back into place. My logic is it was probably pressed in during manufacturing and has slowly backed out over the years. Also as far as I understand any clogging up of the PCV system would cause the engine to run poorly and throw a CEL which I dont have. As far as the aluminum VC it is aftermarket and I wouldn't completely trust it to have all the internal plumbing for the PCV done correctly if at all since it is completely out of sight unless you've verified with the manufacturer. I will continue to monitor the situation and report back with any future developments.
Appreciate the feedback but I am already aware of the PCV routing in the VC. My question is if it would be a wise idea to try to tap the upper VC back into place. My logic is it was probably pressed in during manufacturing and has slowly backed out over the years. Also as far as I understand any clogging up of the PCV system would cause the engine to run poorly and throw a CEL which I dont have. As far as the aluminum VC it is aftermarket and I wouldn't completely trust it to have all the internal plumbing for the PCV done correctly if at all since it is completely out of sight unless you've verified with the manufacturer. I will continue to monitor the situation and report back with any future developments.
yeah I’m definitely taking a gamble on the aluminum VC. But I will let you know how it works out. It looks legit and appears to have all the piping for the built in PCV. Here’s the link to check it out - https://www.ebay.com/itm/17611377652...mis&media=COPY
As for your valve cover, i agree with you. It was definitely pressed or glued on from the factory. I would not try to press it back in. Being plastic and a Mercedes, it’s likely a one and done deal. Just get a new valve cover and gaskets call it a day.
but that’s my personal opinion and what I’m doing. If the aluminum VC doesn’t work out I will get an OEM plastic one again.
This part I would buy a new one. I would probably get it from FCP Euro for the lifetime warranty in case there's any issues down the road. If the new ones fails at any point buy another one, send the failed one back for store credit for the original price you paid.
I think i would go crazy if I had to take it off again as this was the fourth attempt to get this done right. I've had pretty much everything that could go wrong happen to me from new defected gaskets to broken bolts and stripped holes. I think the mallet method could work if I do it after the engine has been running for a while where the VC would be as warm and malleable as possible and then gently try to tap it back into place. Also I recently changed my oil and used the LM Molygen oil with the UV dye so I will be able to better trace the leak with a UV light as my theory of that gap causing the leak is still an assumption.
I put a UV dye in my oil over the summer and think it was a waste. I took a UV flashlight to the engine and all the old oil leaks seemed to be glowing a green color. Then I used the flashlight to compare fresh oil with no dye and old oil with the dye and they basically looked the same. it looks like there is already something in the oil that makes it glow greenish. Have you looked in the engine bay with the UV flashlight before using the dye? I should have.
Here's the thread I made on it. I talked about a few things in it, UV dye, replacing breather covers, replacing oil filter housing gasket. Post# 16 has photos I took looking in the engine bay with a UV flashlight, shows old oil leaks look glowing. So I didn't know what was new or old leaks.
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Valve cover leak!
