Hi, I'm a long-time reader, first-time poster, in need of help. I have a 07 R350 with 195K miles. Owned it since 110K. Mobil1 Euro 0W40 and OEM fleece filter every 6K miles. No problems until recently. I could really use some helpful advice as I'm not sure what to try next.
Last winter the R350's M272 engine would make an occasional deep rattle for a few seconds when starting cold. I've understand this could be the infamous oil pickup tube o-ring. I've only heard that sound a few times on the coldest days, so didn't think much of it. Earlier this summer it developed a new sound, a diesel-like knocking at idle, regardless of air or engine temperature. Exactly like the sound in YouTube video 1X4XuA1LHeY "Mercedes E280 M272 3.0L Engine Knock". I removed the serpentine belt and briefly ran the engine to confirm the sound has nothing to do with the belt or accessories. The knocking becomes louder and speeds up as RPM increases, and can be clearly heard from many feet away, but sometimes goes away entirely around 1800 RPM and above. There is no hesitation or power loss, it still feels as powerful as it did 7 years ago. I understand this could be a collapsed lifter or perhaps a timing chain (or chain tensioner) issue, maybe a cam magnet/adjuster issue. Using a stethoscope I have found the knocking to be loudest around the left/driver-side exhaust cam gear cover area, sort of behind the power steering reservoir. I dumped in a bottle of LiquiMoly after a fresh oil change to no avail, and have been driving it sparingly (once every few weeks) this summer as other projects have kept me from digging deeper.
Last week a new issue or two emerged. Acceleration after a stop light, or even giving it some gas to back out of a parking space, sometimes results in a puff of blue-white smoke from the left/driver-side exhaust. There is sometimes a similar puff when starting it cold. I say blue-white as it doesn't have the ultra white blown head gasket look, nor does it have the blue oil-burner haze to it. It's more like "morning condensation in the exhaust". Just more frequently. The puff is fairly odorless, maybe a bit oily smelling. The engine burns/leaks only a small amount of oil, and the coolant surge tank is still full and clean. The other new issue is an occasional light shudder/hesitation at idle, usually when in drive with the brake held down at a stoplight. Once in awhile the RPM will drop ever so slightly, almost like the engine had to swallow, or like a very very mild EGR issue. The only code is P0333.
I'm not sure what I should do at this point. Check the plugs? Use a borescope to look for cylinder scoring? Install a timing chain kit? Try a thicker oil? Change the knock sensor? Test the fluids to determine if the head gaskets are failing?
I am open to any advice. Thank you so much in advance!

 

Pay to have the problem properly diagnosed before yanking the lanyard on the parts canon.

 

I am guilty as anyone of commanding an artillery battery launching parts into cars.

However, in this case, @JettaRed states, diagnosis should be your next step.

Check the plugs, borescope and check compression can all be done in the same job. Do these yourself or pay an indy shop to do them, and report back.

 

blue smoke means OIL.

 

This might be the problem causing the P0333 DTC. However, it does not account for the smoke. I assume you are using premium (91-93 octane) gas and not regular (87 octane) or the intermediate (89 octane) fuel. But with 195k miles, you can expect some oil burning. The two symptoms may be coincidental.


Again, get the car checked by a qualified mechanic. There may be more serious issues. If there are and the repairs exceed the value of the car, drive it until it dies. Or fix it.