I have come up with a possible reason for what may cause, and or may have caused, the early OM603 aluminum heads, (86-87 300SDL and 87 300D and TD) to develop fractures, cracks, in the aluminum head casting that allow compressed combustion to diminish dramatically and also leak into cooling chambers, ultimately rendering the head as useless!

While there are many original #14 OM603 aluminum heads still installed and in daily use today, many others in the past have suffered what is becoming known as the "603 head crack syndrome" since nobody knows for absolute sure why? We know it's mainly heat related and overheating will do it but in some cases overheat, or boiling over, have not been present.

As I understand it, MB had taken early notice to head cracking issues but never published any detailed info other than to suggest owners were not implementing the recommended 30 second cool down before switching off the ignition. Other related and possible causes could be traced to the early trap oxidizer (calif. mandated) which not only generated more heat, but also threatened to come apart internally (ceramic particles) and get sucked up by the turbo and then rammed into the firing chambers thus damaging the turbo and engine. MB redesigned the trap and recalled all OM 603's for refit, but some owners either ignored the recall or were not aware. I've seen one still installed recently!

At some point early on MB must have realized the 603 heads had an inherent weakness and under certain circumstances were vulnerable to fracture and cracking. Design modifications to the OM603 aluminum head were implemented to reduce or eliminate fractures and cracks from occuring. That production run as I understand it began with #17 up from #14 although I've heard a small number of these #17 heads also had cracked too. Further modifications as I understand were implemented. I'm aware of numbers in the production run going as far up as #22 up from #17. I'm not sure if there was a #15 or #16. MB stopped delivering diesel cars to the US from 1987 through 1990. Later heads have a design modification to the precombustion chamber, and some people here on this forum have been successful machining older PCC's to fit the new heads, which are aftermarket as I understand it. So I'm not sure later production numbers such as #22 are MB, or aftermarket numbers?

More to come.........part 2 wow!

Steve...........................