The Mercedes-Benz S-Class SE (W126, facelift 1985) 350 SD Turbodiesel Automatic represents a unique offering within the renowned W126 S-Class generation. Produced from June 1990 to August 1991, this variant combined the prestige of the S-Class with the fuel efficiency and durability of a turbocharged diesel engine, paired with a convenient automatic transmission. It occupied a middle ground in the W126 lineup, appealing to buyers seeking a luxurious and comfortable grand tourer without the higher costs associated with the gasoline-powered models. This model was primarily aimed at the European market, where diesel engines were favored for their economy and longevity, though limited examples were imported to the United States.
Technical Specifications
| Brand | Mercedes-Benz |
| Model | S-class |
| Generation | S-class SE (W126, facelift 1985) |
| Type (Engine) | 350 SD Turbodiesel (136 Hp) Automatic |
| Start of production | June, 1990 |
| End of production | August, 1991 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Sedan |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Maximum speed | 175 km/h (108.74 mph) |
| Weight-to-power ratio | 13 kg/Hp, 76.8 Hp/tonne |
| Weight-to-torque ratio | 5.7 kg/Nm, 175.1 Nm/tonne |
| Power | 136 Hp @ 4000 rpm |
| Power per litre | 39.4 Hp/l |
| Torque | 310 Nm @ 2000 rpm (228.64 lb.-ft. @ 2000 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | OM 603 D 35 A / 603.970 |
| Engine displacement | 3449 cm3 (210.47 cu. in.) |
| Number of cylinders | 6 |
| Engine configuration | Inline |
| Cylinder Bore | 89 mm (3.5 in.) |
| Piston Stroke | 92.4 mm (3.64 in.) |
| Compression ratio | 22:1 |
| Number of valves per cylinder | 2 |
| Fuel injection system | Multi-port manifold injection |
| Engine aspiration | Turbocharger |
| Valvetrain | SOHC |
| Engine oil capacity | 7.5 l (7.93 US qt | 6.6 UK qt) |
| Coolant | 10 l (10.57 US qt | 8.8 UK qt) |
| Kerb Weight | 1770 kg (3902.18 lbs.) |
| Max. weight | 2240 kg (4938.35 lbs.) |
| Max load | 470 kg (1036.17 lbs.) |
| Fuel tank capacity | 90 l (23.78 US gal | 19.8 UK gal) |
| Length | 5145 mm (202.56 in.) |
| Width | 1820 mm (71.65 in.) |
| Height | 1438 mm (56.61 in.) |
| Wheelbase | 2930 mm (115.35 in.) |
| Front track | 1562 mm (61.5 in.) |
| Rear (Back) track | 1534 mm (60.39 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 | Ventilated discs |
| Rear brakes | Disc |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Cone worm with recirculation balls |
| Power steering | Hydraulic Steering |
| Tires size | Front wheel tires: 205/65 R15Rear wheel tires: 205/65 R15 |
| Wheel rims size | Front wheel rims: 6.5J x 15Rear wheel rims: 6.5J x 15 |
INTRODUCTION
The W126 S-Class, introduced in 1979, represented a significant leap forward in luxury and engineering for Mercedes-Benz. The facelifted version of 1985 brought subtle but important updates to the exterior and interior, enhancing its already sophisticated appeal. The 350 SD Turbodiesel Automatic, launched in 1990, was a late-production model within this facelifted range. It aimed to provide the S-Class experience to buyers prioritizing fuel economy and long-distance comfort. It was positioned as a more affordable alternative to the gasoline-powered 420 SE and 560 SE models, while offering more performance than the naturally aspirated 300 SD.
Powertrain & Engine Architecture
The heart of the 350 SD Turbodiesel is the OM 603 D 35 A inline-six cylinder diesel engine. This engine, displacing 3.5 liters (3449 cc), utilizes a turbocharger to boost power output to 136 horsepower at 4000 rpm and 310 Nm (228.64 lb-ft) of torque at 2000 rpm. The engine features a robust cast iron block and aluminum cylinder head, contributing to its renowned durability. Fuel is delivered via a multi-port manifold injection system, a relatively advanced system for its time, improving combustion efficiency and reducing emissions. The engine employs a single overhead camshaft (SOHC) valvetrain with two valves per cylinder. The automatic transmission is a four-speed unit, designed to provide smooth and effortless gear changes, complementing the diesel engine’s torque characteristics. This transmission was a common choice for Mercedes-Benz vehicles of this era, known for its reliability and durability.
Driving Characteristics
The 350 SD Turbodiesel Automatic offered a distinctly different driving experience compared to its gasoline-powered siblings. While lacking the outright acceleration of the V8 models, it provided ample torque for comfortable cruising and effortless overtaking. The automatic transmission, while not offering the sporty responsiveness of a manual, contributed to a relaxed and refined driving experience. The gear ratios were optimized for fuel efficiency and smooth power delivery. Acceleration was adequate, but the focus was on maintaining a steady speed on the highway. Compared to the 300 SD, the 350 SD offered a noticeable performance improvement thanks to the larger displacement and turbocharging. However, it didn’t match the responsiveness of the 420 SE or 560 SE.
Equipment & Trim Levels
The S-Class SE trim level, even in its diesel guise, was generously equipped. Standard features included power windows, central locking, climate control, and a high-quality sound system. The interior was typically upholstered in leather, with wood trim adorning the dashboard and door panels. The 350 SD Turbodiesel Automatic often came with options such as a sunroof, heated seats, and upgraded audio systems. The level of luxury was comparable to the gasoline-powered models, though some of the more exotic options were less commonly specified on the diesel variants.
Chassis & Braking
The W126 S-Class featured a robust chassis with independent suspension all around. The front suspension utilized a double wishbone design, while the rear employed a trailing arm setup. This configuration provided a comfortable ride and good handling characteristics. The 350 SD, being a heavier vehicle due to the diesel engine, benefited from the well-tuned suspension. Braking was handled by ventilated discs at the front and discs at the rear, providing adequate stopping power. An Anti-lock Braking System (ABS) was standard, enhancing safety and control. The steering was a recirculating ball system with hydraulic power assistance, offering a good balance of feel and ease of use.
Market Reception & Comparison
The 350 SD Turbodiesel Automatic was generally well-received by critics, particularly in Europe, where diesel engines were highly valued. It was praised for its fuel efficiency, comfortable ride, and robust build quality. However, some reviewers noted its relatively modest performance compared to the gasoline-powered models. Compared to the 420 SE and 560 SE, the 350 SD offered significantly better fuel economy but lacked the same level of refinement and acceleration. Against the 300 SD, the 350 SD provided a noticeable power upgrade, making it a more appealing option for those seeking a more capable diesel S-Class.
Legacy
The OM 603 engine family, including the 3.5-liter variant found in the 350 SD, is renowned for its durability and longevity. These engines are known to reliably exceed 300,000 miles with proper maintenance. Today, the W126 S-Class 350 SD Turbodiesel Automatic is a sought-after classic car, particularly among enthusiasts who appreciate its unique combination of luxury, fuel efficiency, and robust engineering. While parts availability can be a challenge, the engine’s inherent reliability and the strong community support for the W126 platform ensure that these vehicles continue to be enjoyed by enthusiasts around the world. The car represents a unique chapter in Mercedes-Benz history, bridging the gap between traditional luxury and the growing demand for fuel-efficient transportation.
