I had this happen on my '98 E300 turbodiesel. It too cost $2500 to repair. The head had to be pulled and the glowplug (one broken off plug) painstakingly removed. Normal glowplug life on this car is about three years. I had the problem when installing set #3 in January 2003. I sold the car after the repair - this problem goes beyond a quirk, it's a design defect.

The problem is not caused by corrosion, it is caused by mechanical retention of the GP via tightly packed carbon around the GP. An OM606 GP is about 6" long, vs. about 2.5" for the 617/601/602/603. The threads of the 606 GP are at the extreme top, very near the electrical connector. The great majority of the GP is in a long, narrow passageway which leads to the combustion chamber. (DOHC four valve engine with centrally located fuel injector - it's a long reach to the center of the combustion chamber.) This passageway becomes packed with carbon during normal operation of the engine. There is sufficient friction between the carbon and the glowplug to restrict its movement. The torque required to turn the glowplug exceeds the torsional strength of the glowplug, and it snaps just above the threads. Alternatively the hex flats round off - a 12mm hex head is not sufficiently robust to transfer the necessary torque. Experienced mechanics know the torque limits of the GP and quit before breaking something.

The carbon is so tight that I had extreme difficulty removing several plugs from the engine even after completely unthreading them. It was necessary to spray penetrating lubricant into the area for about two days before the plug loosened up sufficiently to be removed.

Anyways, that's my story and I'm sticking to it. I can't recommend the OM606 engine with a clear conscience, this problem is just too severe. Besides, it needs GPs so often, it's cheaper to drive an E320 with the M112 engine. The better fuel economy of the diesel doesn't offset the higher maintenance cost.

- JimY