PeterinCO,

You are correct, there is a reason. Unfortunately it is not in MB's best interest to share it with us, so it is highly unlikely we will find out the real reason soon.

For my money, I think it is a combination of things associated with the design and the manufacturing process. I am not a subscriber to the carbon ingestion theory because carbon is a problem that has been available to bend rods on the first of these engines equipped with exhaust gas recirculation, and none of them exhibited the tendency to bend rods before this engine. I believe the rods are flawed by the stack up of design and manufacturing tolerances on dimensions, metallurgy (chemistry and heat treatment) that make rods with certain combinations bad. Others are apparently ok.

Merely thickening them is not always the answer as depending on where the thickening is done, the loads can increase faster than the mechanical properties, leading to a net change in the fringes of when it happens. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)