Originally Posted by Jeremy5848

As for the relative reliability of the 606 vs the 603, it's mostly a matter of the alloy head learning curve at Daimler-Benz. The later 606 engine got all of the improvements that were gradually introduced in the various versions of the 603 head. Additionally, the 606NA engine is less stressed than the turbo 603. [Did Europeans and other who got 603NA engines have the same problems?] A 603 with a late-model head and head gasket should be just as reliable as a 606. Both are similarly vulnerable to overheating, I suspect. I haven't heard bad things about the 98-99 turbo 606 so they must have learned their lesson.

In any case, my preference for the 603 turbo over the 606NA is not so much for reliability as for performance and DIY-ability. The W210/OM606NA is much more electronic than the W124/OM603 turbo and the 98-99 turbo 606 is even worse. In California, '98-up diesels even have to be smogged (biannually)! One of the great joys of an older diesel is not having to smog it. The turbo 606 is even more powerful than the turbo 603, of course, but I've never driven one. It would be interesting to put a turbo 606 in a 1995 W124 chassis but I think the electronics are difficult to eliminate. Pity.

It's late. I'm tired. Good night.

Jeremy