The Mercedes-Benz C123 300 CD Turbodiesel Automatic, produced between October 1982 and August 1985, represents a unique and sophisticated offering within the broader W123 series. This coupe variant, distinguished by its two-door body style, combined the luxury and build quality expected of Mercedes-Benz with the fuel efficiency and torque characteristics of a turbocharged diesel engine. Positioned as a premium offering within the C123 range, it catered to buyers seeking a comfortable, long-distance grand tourer with an emphasis on economy. The 300 CD Turbodiesel was a relatively short-lived model, bridging the gap between the earlier naturally aspirated diesels and the later, more powerful iterations.
Technical Specifications
| Brand | Mercedes-Benz |
| Model | W123 |
| Generation | C123 |
| Type (Engine) | 300 CD Turbodiesel (125 Hp) Automatic |
| Start of production | October, 1982 |
| End of production | August, 1985 |
| 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 kg/Hp, 76.9 Hp/tonne |
| Weight-to-torque ratio | 6.5 kg/Nm, 153.8 Nm/tonne |
| Power | 125 Hp @ 4350 rpm |
| Power per litre | 41.7 Hp/l |
| Torque | 250 Nm @ 2400 rpm (184.39 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 Turbodiesel is the OM 617 D 30 A engine, a 3.0-liter inline-five cylinder diesel. This engine, also known by its code 617.952, was a significant evolution of Mercedes-Benz’s established diesel technology. The OM617 featured a robust cast iron block and head, designed for longevity and high compression ratios (21.5:1 in this application). The addition of a turbocharger, along with intercooling, boosted power output to 125 horsepower and 184 lb-ft of torque. Fuel injection was handled by a Bosch multi-port mechanical injection system, providing precise fuel delivery for optimal combustion. The single overhead camshaft (SOHC) valvetrain operated two valves per cylinder. The automatic transmission was a four-speed unit, designed to handle the engine’s substantial torque output. This transmission was not known for its sportiness, prioritizing smooth shifts and reliability over rapid acceleration.
Driving Characteristics
The 300 CD Turbodiesel Automatic offered a distinctly different driving experience compared to its gasoline-powered siblings or even the non-turbocharged diesel versions. While not a performance 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 mph. The automatic transmission, while smooth, contributed to a somewhat leisurely pace. The gear ratios were optimized for fuel economy and relaxed cruising, rather than spirited driving. The engine excelled at providing strong low-end torque, making it well-suited for highway driving and towing. However, the engine could become noisy and vibrate noticeably at higher RPMs.
Equipment & Trim Levels
The C123 300 CD Turbodiesel Automatic was generally well-equipped for its time. Standard features typically included power steering, central locking, electric windows, and a high-quality sound system. Interior upholstery was usually a durable cloth or optional leather. The dashboard layout was typical of Mercedes-Benz in the early 1980s, featuring a classic analog instrument cluster and wood trim. Optional extras included a sunroof, air conditioning, and upgraded audio systems. The overall ambiance was one of understated luxury and refinement.
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 provided a comfortable ride, although the car’s weight (approximately 3583 lbs) could be felt in corners. Braking was accomplished by disc brakes on all four wheels, offering adequate stopping power for the vehicle’s weight and performance. Power-assisted steering was standard, making the car relatively easy to maneuver.
Market Reception & Comparison
The C123 300 CD Turbodiesel Automatic was generally well-received by automotive critics, who praised its fuel economy, comfortable ride, and build quality. However, some criticized its relatively slow acceleration and the engine’s noise levels. Compared to the gasoline-powered C123 models, the diesel offered significantly better fuel economy but less performance. Compared to the naturally aspirated 300D, the turbo diesel provided a substantial boost in power and torque. The 300 CD was positioned as a more practical and economical alternative to the more expensive and performance-oriented C123 coupes.
Legacy
The OM617 engine, in its various forms, is renowned for its durability and longevity. Many examples have surpassed 300,000 miles with proper maintenance. The C123 300 CD Turbodiesel Automatic has become a sought-after classic among Mercedes-Benz enthusiasts, particularly those who appreciate the unique combination of luxury, fuel efficiency, and robust engineering. While parts availability can be a challenge, the engine’s simplicity and robust construction make it relatively easy to maintain. Today, well-maintained examples command a premium in the used car market, representing a piece of automotive history and a testament to Mercedes-Benz’s engineering prowess.
