Hello Guys. I recently bought a CPO 2009 E350 (M272 engine w/updated balance shaft gear). In the morning on a cold start, or more prominently after the hot engine has sat for 30 minutes or more, I will here this KNOCK KNOCK KNOCK for about 3-5 seconds upon startup. It definitely sounds like a lower end issue, NOT a valve train "tap". The car is under warranty and has been to the dealer TWICE for this issue only for them to tell me either "no problem found" or "its normal". Now, I HAVE heard and read about many other cars doing this with the same engine. I still don't think that makes it acceptable on a 50K plus car. My indy thinks it is bad crank bearings, causing the crank to move fore and aft, and always says when I leave (the car knocks so loud on startup he hears it from his office), you better get that fixed before your warranty runs out.

I bought it CPO with 34K on it. Currently it has 41K. I have done two oil changes, both with the recommended Mobil 1 Syn 0W-40. I cut the maintenance interval to 5000 instead of the MB recommended 10K. Maybe its a waste of money but that's neither here nor there.

I am concerned obviously for when the warranty is up and question the longevity of this engine. Clearly this is not normal. It is downright embarrassing trying to explain to passengers "Oh that's normal" on such a newer car with warranty. In typical Mercedes USA fashion, they will DENY DENY DENY (look at the balance shaft issue that covered ALOT of M272's).

Has anyone confirmed WHAT is actually causing it? My indy told me has a client who bought a brand new one for his wife and actually had MB buy it back because his was knocking all the time (not just at startup). Same year and model as mine. I recently heard a brand new CLS550 startup near me at the local Staples and his did the same thing (V8 engine). What is with these newer engines? Now I guess there is a TSB out for the new (2012+) 3.5 direct injected motors that effects the wrist pin bearings, etc, and require a rebuild!

What course of action do I have? Try a different dealer? Call MB (they don't care). Request regional field rep to be onsite? I feel MB is pushing me away until the warranty has run out to protect themselves from a new engine or rebuild. Mine is so loud when it does it, it makes my 300D Turbo (with 273K) sound like a brand new Lexus LS.

Any help would be greatly appreciated!

Thankyou.

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93 300D 2.5 Turbo, Black/Palomino 273K
09 E350 Black/Black 41K