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Blown out crankcase breather seals instead of rear main seal failure
Had a client come to us here in Florida after having Hpfp upgrade, aftermarket turbos, tunes etc on his 2018 e63
he mentioned he was told he had a big oil leak from his turbo oil lines. The drain lines aren’t too easy to see clearly without turbos removed so I verified oil was indeed originating in or around this area around the top of the engine and agreed to dig into it
i have seen and replaced rear main seals and crankcase breathers before but this is a failure I haven’t seen before. It looks like the crankcase was overpressurized to the point that instead of blowing out the RMS, instead it blew out the seals of the crankcase breather boxes where they plug into the crankcase
the orange piece off to the side (right side) is a broken piece of the orange seals from the breather boxes
thought I’d share since I haven’t seen this mentioned among any of my old mb dealer tech coworkers or amongst the aftermarket world. Will be recommending new crankcase breathers and possibly an aftermarket PCV system to help cope with the pressure building in the crankcase
I was under the impression that failed OVS's caused excess vacuum, not pressure. This vacuum sucks the RMS seal flange around the bearing to suck in and then it leaks. Could be wrong though. How much boost are you running, could an overboost situation have caused this? Regardless 63 Motorsports sells an aftermarket catch can for this situation.
I was under the impression that failed OVS's caused excess vacuum, not pressure. This vacuum sucks the RMS seal flange around the bearing to suck in and then it leaks. Could be wrong though. How much boost are you running, could an overboost situation have caused this? Regardless 63 Motorsports sells an aftermarket catch can for this situation.
im not sure where the “seal sucks in” narrative comes from… in normal operation, front and rear main seals are folded inwards against the crankshaft, it’s why you need a special tool (or Mercedes is kinda enough to include a plastic guide in the rms trackage that doubles as an installation guide) to prevent the seal from rolling(flipping outwards) as it slides over the crankshaft. The rear main seals ive seen that dump out oil are blown outwards from what appears to be an over pressurization situation. You’ll see about a one inch long section of the seal curled outwards and after that it never holds oil properly again
I haven’t measured boost on this engine but whoever installed the upgraded turbos on this car found it necessary to replace the intake manifold couplers that are known to blow off under high boost…
Interesting, thanks for the information. I just had the RMS done on my 2019 S63 and the dealer refused to replace the OVS claiming that they tested fine. Oh Well, they will be on the hook if it fails in the next year, then my warranty will be on the hook as they also denied the OVS replacement.
Interesting, thanks for the information. I just had the RMS done on my 2019 S63 and the dealer refused to replace the OVS claiming that they tested fine. Oh Well, they will be on the hook if it fails in the next year, then my warranty will be on the hook as they also denied the OVS replacement.
if there is one thing I learned working for mb. They will find a way to consider the oil separators “wear and tear” items eventually and not cover them. I had a sizable argument with some of my managers there because “oil must be dropping onto the ground” for it to be considered a repair covered under warranty. Everything else is “seepage”
That makes my back ache. Hours bent over disconnecting this, disconnecting that, knowing all along I'd have to put it all back together.
I agree first time I did these breather boxes I didn’t want to break any of the plastic bits (everything is made of plastic on these it seems) so I just opted to drop the entire engine to replace the breather boxes. Years later trying it this way without dropping the engine and I don’t really find it that much faster
Dealers make up their own rules, another demonstration of their corruption. I forced an SA to reseal the leaking cylinder head covers on my W166 and oil was not falling to the ground.
It is entirely clear that blowby management on the LS2 engine is inadequate. RMS, breather seals and other seal failure modes have been reported with the LS2 variant. Another MB engineering fail, added to the mountain of recent and past fails.
Dealers make up their own rules, another demonstration of their corruption. I forced an SA to reseal the leaking cylinder head covers on my W166 and oil was not falling to the ground.
It is entirely clear that blowby management on the LS2 engine is inadequate. RMS, breather seals and other seal failure modes have been reported with the LS2 variant. Another MB engineering fail, added to the mountain of recent and past fails.
dealers don’t really make the rules, but they do add discretion based on guidelines from MB. Dealers have a system we checked to see what is covered and what is not covered. Last thing a dealer wants is to pay for a repair out of their own pocket because MB refuses to reimburse them under warranty guidelines. This can sometimes be as simple as a technician or parts department forgetting to bill out $15 in one-time use bolts. Even if the tech had some extra bolts in his toolbox and DID replace them during the repair, MB can kick the labor claim because the documentation doesn’t show the work was done “correctly”.
I paid top dollar for my 2019 c43 during covid times , and while they agreed to spend over $6500 on getting the car back to CPO/like-new standards, they refused to allow me to reseal my cam covers under warranty due to them only “seeping” and not dripping onto the ground. My front differential pinion seal leak was covered under warranty because it was flinging fluid everywhere
the service advisor you “forced” likely had permission from the service director to direct some of their monthly “goodwill repair budget” towards resealing your cam covers. This is typically reserved for highly valued repeat customers, or customers they know are problematic. This is why it pays sometimes to use the same dealer, especially the one you bought the car from
Last edited by ctravis595; Aug 17, 2025 at 03:13 PM.
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