I'm bumping this so it does not fall off the edge of the earth. This thread is a prime example of those with little knowledge of engines falsely accusing a shop of wrong doing

One has to agree this had nothing to do with the oil change. Circumstance where the piston finally just totally let go perhaps.

My original thought was far too thin of an oil may have caused more blowby than normal. This shuts down the engine basically or limits it to extremely low power with the excess blowby. Attempting to shut off the injection pump. Not that the thinner oil did any form of mechanical damage.

When buying a used engine for a 616, 617 or 603. A compression test is almost mandatory. The odometer readings are not to be trusted at all. So a pretty worn engine will still sound reasonable. Yet wear wise may be very long in the tooth.

I have never experienced more liars than when it comes to the car business. Most knowingly doing this unfortunately. So you have to do your homework.

I used to ride a Suzuki 2 cycle, 3 cylinder motorcycle, and it had a long tube with holes in it inside the muffler. I had no idea what the rational was to have that tube in the muffler. I do know I had to periodically clean the tube and make sure that the holes were clear. I was on my way home from work one day, and all of a sudden the bike started losing power. The bike would not go more than 40 mph. After I got home, I pulled the cylinders, and found a hole about the size of a quarter in the top of the middle number 2 cylinder piston. An examination of the exhaust tube mentioned above showed that most of the holes in the tube were clogged and must have caused back pressure in the exhaust which caused the hole in the piston. Replaced the piston, cleaned the tube, and everything was back to normal.

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96 E300d