Originally Posted by Jeremy5848

If I could be picky here, the TURBO 606 is more powerful than the 603 but the NA version in the '95 W124 and the '96-97 W210 has less power and feels like it has much less power. You have to let the 606NA engine wind up before you get any power out of it, it lacks the low-end oomph of the 603. I own both, I know.

Otherwise, the 606 has no significant problems, especially no head problems. In both NA and turbo versions it is more economical than the 603. As PawoSD says, there can be o-ring and fuel line problems (I have had some) but these are things you can fix yourself. I have not had any stuck glow plugs (have replaced only two so far) but others have and it can be a problem.

Jeremy