No one really knows for sure why it happens, or why it only happens here in the States and not in Europe, but the one thing that's different, for sure, that you can point to, is the fact that Euro diesel is 50 cetane and ours varies right around 45, with 48 being premium, and between 40-42 being acceptable. California CARB diesel is 50 cetane, though, which is why Black Death is nearly non-existent in California, and only adds credence to the cetane being the cause.
Fortunately, it's very rare in any case. But, it's something to watch out for. You should periodically remove the plastic cover from the top of the engine, Allen head screws, and check for early signs of Black Death. The earlier you catch it the better. Some recommend every oil change, but I dunno. I check mine every 3 or 4 months. So far so good.
The reason that it's a problem when it happens is, the pure carbon goo isn't gooey. It's 2 degrees and 3 pounds pf pressure away from being diamonds. So it's not like you can take a greasy rag and wipe it off. It cements the injectors in the cylinders to the head, so even if you wanted to change them and the seals out, you can't, 'cause they break off when you try to remove them. If left alone, the pressure finally just cracks the head. But, fortunately, like Aileron said, there's a guy in Pittsburgh who invented a tool that deals with it quite nicely, removes the injectors and saves the head.
But like I said, it's rare that it happens at all. I don't know the numbers, but it's a very small percentage.
