Please reference this thread for a full explanation of what the engine numbers mean.

Herein, you will see various references to the letter W followed by a 3-digit number (i.e. W123, W126, W210, etc). These are chassis numbers used primarily internally by M-B, but are also commonly used on various websites, so it's a good idea to at least know the chassis number of the vehicle you own or are thinking about buying. The full chassis number is actually 6 digits, with the last three digits differentiating between various sub-bodystyles and engine offerings. More details on that below. Also, take a look here. Note that the chassis number is unique to a specific bodystyle; for instance, a W126 is the chassis number for the S-class sedan built between 1981 and 1991, but a 1992 S-class is a W140 chassis. (confused yet?) The model number you see on the trunk usually refers to the engine size (a 240D, for example, indicated a 2.4l engine), with the letter at the end indicating a specific engine characteristic. “D” means “diesel”, “E” essentially means an EFI gas engine, and no letter at all indicates a carbureted gas engine. Other letters used in the suffix (usually in conjunction with the aforementioned letters) have various meanings. For instance, “T” (“touring”) indicates a station wagon (NOT turbo), “S” (S-Class) indicates a full-size car, “C” indicates a coupe, “SL” indicates a convertible roadster (you won’t find an “SLD”, though), etc.

I'll start with the midsize car, since they're the most common. There was not originally a letter suffix associated with the midsize car, but after EFI gasoline engines were introduced, the letter “E” began being used on gasoline-powered models. After the vehicle model numbers were revamped in 1993 or so, the “E” was affixed to all midsize cars, and the midsize car is known today as the E-class.

W120/121
These cars are known as the “Pontons”, the nickname comes from the German word for "pontoon" and refers to one definition of pontoon fenders. These cars were sold between 1953 and 1962. Engines were mated to, I believe, 4 speed column-shift manual transmissions, and while these cars were fairly basic even by 1950’s standards, they were considered the epitome of reliability at the time, and were cherished by people in spite of the lethargic performance acquired from the engines that were rated at around 60 horsepower. The model numbering system is unique in these cars in that a lower-case letter was used to denote series improvements. A few other M-B chassis in the late 1950’s used this as well, but it disappeared in the early 1960’s. Cars built in this chassis include:

* 180D and 180Db: W120.110 chassis, powered by an OM636.930 engine (see above). Built between 1953 and 1961. Curb weight: 2508 lbs.
* 180Dc: W120.110 chassis, powered by an OM621.914. Built between 1961 and 1962. Curb weight: 2508 lbs.
* 190D and 190Db: W121.110 chassis, powered by an OM621.910. Built between 1959 and 1961. Curb weight: 2670 lbs.


W110
Much like the W120 and W121 Pontons, the “Fintail” or "Heckflosse" W110 was considered reliable if lethargic, coupling comparatively small engines to 4 speed column-shift manual transmissions and built to very basic standards. M-B was behind the times in that they introduced small “fins” to their cars after fins had largely gone out of style in America, with the W110 being one of the only M-B’s to sport this design. The W110 was built between 1962 and 1968. Cars built in this chassis include:

* 190Dc: W110.110 chassis, powered by an OM621.912. Built between 1962 and 1965.
* 200D: W110.110 chassis, powered by an OM621.918. Built between 1966 and 1967.


W114/115
The W114 and W115 is, by today’s standards, much closer to contemporary styling than the Pontons and Fintails that preceded it. These cars are relatively common in the United States as compared to the earlier diesels offered, and are still common in Europe and elsewhere in the world. The basic design is similar between the W114 and the W115, and they were both built between 1968 and 1976. All diesel models and 4-cylinder gas models are W115’s; all 6-cylinder gas models are 114’s. It appears that this is the first M-B offered in the U.S. with an automatic transmission as an option with a diesel. Also, the gearshift for the manual as well as for the auto were moved to the floor from the column. Both the manual and the automatic transmissions had 4 forward gears, with the top gear ratio at 1:1 (no overdrive). Cars built in this chassis include:

* 200D: W115.115 chassis, powered by an OM615.913. Likely built between 1968 and 1973, but that’s not known for sure. Curb weight: 3003 lbs. Unsure on transmission availability (but likely either only offered with a manual or available with either transmission)
* 220D: W115.110, powered by an OM615.912. Built between 1968 and 1973. Curb weight: 3110 lbs. Available with either transmission.
* 240D: W115.117, powered by an OM616.916. Built between 1973 and 1976. Curb weight: 3205 lbs. Available with either transmission.
* 300D: W115.114, powered by an OM617.910. Built between 1975 and 1976. Curb weight: 3450 lbs. Available only with an automatic trans.


W123 (sedan) (wagon) (coupe)
The W123 is considered a legend by many, and there are those who contend that it is the last of the “indestructible” Mercedes designs. This car was designed with reliability, comfort, functionality, and ease of maintenance in mind. Unlike other Mercedes models, nearly all W123’s sold in the United States were diesel-powered (in fact, they stopped even trying to market a gas-powered W123 in the U.S. after 1983). Styled after the larger W116 model described below, is by far the most common Mercedes seen in the United States even today. The W123 is commonly used in Europe and elsewhere around the world as a taxi, with some European taxis recording odometer readings equivalent to 1,000,000 miles (yes, that’s 1 million). As with the W115, the W123 was sold with either a 4 speed auto or a 4 speed manual transmission, depending on the engine and on customer preference. Also, on 5 cylinder diesel W123 models, power windows, a power sunroof, cruise control, and an automatic climate control system became standard equipment (the power windows, sunroof, and cruise control were optional on 4 cylinder W123’s). The W123 was sold between 1977 and 1985. Cars built in this chassis include:

* 240D: 123.123 chassis, powered by an OM616.912. Built between 1977 and 1983. Curb weight: 3250 lbs. Available with either transmission.
* 300D: 123.130 chassis, powered by an OM617.912. Built between 1977 and 1981. Curb weight: 3515 lbs. Available only with an automatic trans.
* 300D Turbo: 123.133 chassis, powered by an OM617.952. Built between 1982 and 1985. Curb weight: 3515 lbs. Available only with an automatic trans. Note that the 1985 W123 (and W126, described below) is the last Mercedes diesel sold in the U.S. with an all cast-iron engine.
* 300CD: 123.150 chassis, powered by an OM617.912. Built between 1978 and 1981. Curb weight: 3475 lbs. Available only with an automatic trans. This is the first (and, with the one below, the only) MB coupe available with a diesel engine.
* 300CD Turbo: 123.153 chassis, powered by an OM617.952. Built between 1982 and 1985. Curb weight: 3495 lbs. Available only with an automatic trans.
* 300TD: 123.190 chassis, powered by an OM617.912. Built between 1979 and 1981. Curb weight: 3740 lbs. Available only with an automatic trans. This is the first M-B station wagon sold in the United States. Note that, in spite of the same engine model number, the OM617 in a 300TD has a minor difference as compared to the OM617 in a 300D or a 300CD. There is a hydraulic pump integrated into the cylinder head on any engine out of a 300TD, to pressurize the hydraulic self-leveling suspension that was standard equipment on all W123 station wagons sold in the U.S. This difference means that an OM617 out of a 300TD can be used in a 300D or a 300CD, but you cannot use an OM617 out of a 300D or a 300CD in a 300TD without disabling the self-leveling suspension or changing the cylinder head to one out of a 300TD.
* 300TD Turbo: 123.193 chassis, powered by an OM617.952. Built between 1981 and 1985. Curb weight: 3780 lbs. Available only with an automatic trans. See note for 300TD above.