The Mercedes-Benz C123 300 CD Turbodiesel Automatic, produced from July 1981 to October 1982, represents a unique and relatively short-lived variant within the broader W123 series. Positioned as a luxury coupe, the C123 chassis offered a more sporting aesthetic than the contemporary W123 sedan and wagon models. This particular iteration, powered by the OM617 diesel engine and paired with an automatic transmission, aimed to deliver a blend of fuel efficiency, comfortable cruising, and the prestige associated with the Mercedes-Benz brand. It occupied a niche position, appealing to buyers seeking a refined, economical coupe without sacrificing the robust engineering for which Mercedes-Benz was known.
Technical Specifications
| Brand | Mercedes-Benz |
| Model | W123 |
| Generation | C123 |
| Type (Engine) | 300 CD Turbodiesel (121 Hp) Automatic |
| Start of production | July, 1981 |
| End of production | October, 1982 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Coupe |
| Seats | 4 |
| Doors | 2 |
| Fuel Type | Diesel |
| Acceleration 0 – 100 km/h | 14 sec |
| Acceleration 0 – 62 mph | 14 sec |
| Acceleration 0 – 60 mph | 13.3 sec |
| Maximum speed | 165 km/h (102.53 mph) |
| Weight-to-power ratio | 13.4 kg/Hp, 74.5 Hp/tonne |
| Weight-to-torque ratio | 7.1 kg/Nm, 141.5 Nm/tonne |
| Power | 121 Hp @ 4350 rpm |
| Power per litre | 40.4 Hp/l |
| Torque | 230 Nm @ 2400 rpm (169.64 lb.-ft. @ 2400 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | OM 617 D 30 A / 617.952 |
| Engine displacement | 2998 cm3 (182.95 cu. in.) |
| Number of cylinders | 5 |
| Engine configuration | Inline |
| Cylinder Bore | 90.9 mm (3.58 in.) |
| Piston Stroke | 92.4 mm (3.64 in.) |
| Compression ratio | 21.5:1 |
| Number of valves per cylinder | 2 |
| Fuel injection system | Multi-port manifold injection |
| Engine aspiration | Turbocharger |
| Valvetrain | SOHC |
| Engine oil capacity | 9.5 l (10.04 US qt | 8.36 UK qt) |
| Coolant | 11 l (11.62 US qt | 9.68 UK qt) |
| Kerb Weight | 1625 kg (3582.51 lbs.) |
| Max. weight | 2080 kg (4585.62 lbs.) |
| Max load | 455 kg (1003.1 lbs.) |
| Fuel tank capacity | 80 l (21.13 US gal | 17.6 UK gal) |
| Length | 4763 mm (187.52 in.) |
| Width | 1786 mm (70.31 in.) |
| Height | 1395 mm (54.92 in.) |
| Wheelbase | 2710 mm (106.69 in.) |
| Front track | 1488 mm (58.58 in.) |
| Rear (Back) track | 1446 mm (56.93 in.) |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels of the vehicle. |
| Drive wheel | Rear wheel drive |
| Number of gears and type of gearbox | 4 gears, automatic transmission |
| Front suspension | Double wishbone |
| Rear suspension | Trailing arm |
| Front brakes | Disc |
| Rear brakes | Disc |
| Steering type | Cone worm with recirculation balls |
| Power steering | Hydraulic Steering |
| Tires size | Front wheel tires: 195/70 R14Rear wheel tires: 195/70 R14 |
| Wheel rims size | Front wheel rims: 6J x 14Rear wheel rims: 6J x 14 |
Powertrain & Engine Architecture
The heart of the C123 300 CD was the OM617 D 30 A engine, a 3.0-liter inline five-cylinder diesel. This engine was a cornerstone of Mercedes-Benz’s diesel offerings throughout the 1970s and 80s, renowned for its durability and longevity. The “D 30 A” designation indicated the increased displacement and power output achieved through turbocharging. The engine utilized a Bosch multi-port manifold injection system, a relatively advanced system for its time, contributing to improved combustion efficiency and reduced emissions compared to earlier diesel designs. The single overhead camshaft (SOHC) valvetrain operated two valves per cylinder. The turbocharger, a Garrett unit, significantly boosted power output to 121 horsepower and 230 Nm (169.64 lb-ft) of torque. The automatic transmission was a four-speed unit, designed to provide smooth and comfortable shifts, prioritizing ease of driving over outright performance.
Driving Characteristics
The 300 CD Automatic offered a distinctly different driving experience compared to its gasoline-powered counterparts or even the manual diesel versions. While not a sports car, the turbocharger provided a noticeable surge of power, particularly in the mid-range. Acceleration to 60 mph took around 13.3 seconds, and top speed was approximately 102.53 mph. The automatic transmission, while smooth, did sap some performance, resulting in slightly slower acceleration times than the manual transmission equipped models. The focus was on relaxed cruising and effortless highway travel. The torque converter allowed for smooth takeoffs and minimized the need for frequent gear changes. However, the transmission’s shift points were not always optimized for performance, sometimes feeling hesitant during overtaking maneuvers.
Equipment & Trim Levels
The C123 300 CD Automatic was generally well-equipped for its era, reflecting Mercedes-Benz’s commitment to luxury. Standard features included power steering, disc brakes on all four wheels, and comfortable cloth upholstery. The interior was characterized by its classic Mercedes-Benz design, with wood trim accents and a functional, yet elegant dashboard layout. Optional extras included leather upholstery, air conditioning, a sunroof, and upgraded audio systems. The trim level was generally consistent across the 300 CD models, with options allowing buyers to personalize their vehicles.
Chassis & Braking
The C123 chassis featured independent suspension all around, with double wishbones at the front and a trailing arm setup at the rear. This configuration provided a comfortable ride and good handling characteristics. The car’s weight of 1625 kg (3582.51 lbs) was substantial, but the suspension effectively managed body roll and provided a stable platform. All four wheels were equipped with disc brakes, offering strong and reliable stopping power. Hydraulic power steering made maneuvering at low speeds easier, while maintaining a reasonably direct feel at higher speeds.
Market Reception & Comparison
The C123 300 CD Turbodiesel Automatic received generally positive reviews from automotive critics. It was praised for its fuel efficiency, comfortable ride, and refined interior. However, some critics noted the relatively modest performance compared to gasoline-powered coupes. Compared to the 300 CD with a manual transmission, the automatic version offered less driver engagement and slightly reduced fuel economy. Against other coupes in its class, the 300 CD stood out for its robust build quality and diesel engine’s longevity. The diesel engine was a significant selling point for buyers prioritizing fuel economy and long-term reliability.
Legacy
The OM617 engine, found in the C123 300 CD, has earned a reputation as one of the most durable and reliable diesel engines ever produced. Many examples have surpassed 300,000 miles with proper maintenance. Today, the C123 300 CD is a sought-after classic car, particularly among Mercedes-Benz enthusiasts. The automatic transmission, while not as desirable to some as the manual version, remains relatively reliable. Parts availability is generally good, although some specific trim pieces can be difficult to find. The C123 300 CD represents a unique chapter in Mercedes-Benz history, combining luxury, fuel efficiency, and the legendary durability of the OM617 diesel engine.
