That old system must have been driving those Germans nuts.
The tendency among German luxury automakers to use only alphanumeric nomenclature for their cars makes for model names that are - in theory - very easy to understand. But once the automaker strays from this system a bit, the whole thing can become a jumbled mess. This is why Mercedes-Benz has announced a new naming system, intended to clear up any confusion about any given vehicle's purpose.
This restructuring mainly focuses on the company's line of SUVs. The G-Class will keep its name, but the rest of the lineup now has a third letter, which corresponds to a sedan class letter, designating size. There will also be a lower-case letter added to the end of several models. A "d" will designate diesel, an "h" hybrid, "f" for fuel cell, "e" for electric and "c" for compressed natural gas. Gasoline vehicles won't get a lower-case designator. This might all look a bit complicated right now, but we expect (and Mercedes hopes) that this will all get a lot easier to keep straight once you get used to it.