The Mercedes-Benz 420 SEC, part of the C126 series facelift produced from September 1987 to October 1991, represented a luxurious and powerful grand touring coupe. Positioned as a mid-to-high range offering within the C126 lineup – which also included the 300 SEC and 560 SEC – the 420 SEC combined a substantial V8 engine with a comfortable, well-appointed interior and the convenience of an automatic transmission. This model aimed to deliver a refined driving experience for those seeking both performance and prestige. The C126 generation itself was a significant step forward for Mercedes-Benz, establishing many of the design cues and technological features that would define the S-Class for decades to come.
Technical Specifications
| Brand | Mercedes-Benz |
| Model | S-class |
| Generation | S-class Coupe (C126, facelift 1985) |
| Type (Engine) | 420 SEC V8 CAT (224 Hp) Automatic |
| Start of production | September, 1987 |
| End of production | October, 1991 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Coupe |
| Seats | 4 |
| Doors | 2 |
| Fuel consumption (urban) | 15.4 l/100 km (15.3 US mpg, 18.3 UK mpg, 6.5 km/l) |
| Fuel consumption (extra urban) | 9.1 l/100 km (25.8 US mpg, 31 UK mpg, 11 km/l) |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0 – 100 km/h | 8.3 sec |
| Acceleration 0 – 62 mph | 8.3 sec |
| Acceleration 0 – 60 mph | 7.9 sec |
| Maximum speed | 220 km/h (136.7 mph) |
| Weight-to-power ratio | 7.2 kg/Hp, 138.3 Hp/tonne |
| Weight-to-torque ratio | 5 kg/Nm, 200.6 Nm/tonne |
| Power | 224 Hp @ 5400 rpm |
| Power per litre | 53.4 Hp/l |
| Torque | 325 Nm @ 4000 rpm (239.71 lb.-ft. @ 4000 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | M 116 E 42 / 116.965 |
| Engine displacement | 4196 cm3 (256.06 cu. in.) |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Cylinder Bore | 92 mm (3.62 in.) |
| Piston Stroke | 78.9 mm (3.11 in.) |
| Compression ratio | 10:1 |
| Number of valves per cylinder | 2 |
| Fuel injection system | Multi-port manifold injection |
| Engine aspiration | Naturally aspirated engine |
| Valvetrain | SOHC |
| Engine oil capacity | 8 l (8.45 US qt | 7.04 UK qt) |
| Coolant | 12.5 l (13.21 US qt | 11 UK qt) |
| Kerb Weight | 1620 kg (3571.49 lbs.) |
| Max. weight | 2140 kg (4717.89 lbs.) |
| Max load | 520 kg (1146.4 lbs.) |
| Fuel tank capacity | 90 l (23.78 US gal | 19.8 UK gal) |
| Length | 4935 mm (194.29 in.) |
| Width | 1828 mm (71.97 in.) |
| Height | 1407 mm (55.39 in.) |
| Wheelbase | 2850 mm (112.2 in.) |
| Front track | 1555 mm (61.22 in.) |
| Rear track | 1527 mm (60.12 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: 7J x 15Rear wheel rims: 7J x 15 |
Powertrain & Engine Architecture
The heart of the 420 SEC was the M116 E 42 engine, a 4.2-liter naturally aspirated V8. This engine, a cornerstone of Mercedes-Benz’s engineering prowess, featured a single overhead camshaft (SOHC) design per bank of cylinders and utilized Bosch K-Jetronic multi-port fuel injection. The K-Jetronic system, while complex, was known for its reliability and ability to deliver smooth power. The engine produced 224 horsepower at 5400 rpm and 325 Nm (239.71 lb-ft) of torque at 4000 rpm. The 10:1 compression ratio contributed to the engine’s responsiveness. Paired with the engine was a four-speed automatic transmission, designed for smooth and effortless shifting. This transmission was a typical torque-converter type, prioritizing comfort over outright performance.
Driving Characteristics
The 420 SEC Automatic offered a distinctly grand touring experience. While not as overtly sporty as some of its competitors, the combination of the V8 engine and automatic transmission provided ample power for comfortable highway cruising and confident overtaking. Acceleration to 60 mph took approximately 7.9 seconds, and the car could reach a top speed of 220 km/h (136.7 mph). The automatic transmission, while smooth, did result in some power loss compared to the manual transmission options available in other C126 models. Gear ratios were optimized for relaxed cruising, with a focus on providing strong torque in the mid-range. The car felt substantial and planted on the road, offering a secure and stable ride.
Equipment & Trim Levels
The 420 SEC came standard with a high level of equipment, befitting its luxury status. Leather upholstery was standard, as were power windows, power locks, and a sunroof. Climate control was also a standard feature, providing a comfortable cabin environment. Optional extras included upgraded sound systems, heated seats, and a self-leveling suspension system. Interior trim options typically included wood veneer accents, adding to the car’s sophisticated ambiance. The dashboard layout was typical of the era, featuring analog gauges and a straightforward control layout.
Chassis & Braking
The C126 chassis featured independent suspension all around, with a double wishbone setup at the front and a trailing arm arrangement at the rear. This suspension design provided a comfortable ride while maintaining good handling characteristics. Brakes were ventilated discs at the front and solid discs at the rear. An Anti-lock Braking System (ABS) was standard, enhancing safety and control during hard braking. Steering was via a cone worm and recirculation ball system with hydraulic power assistance, providing a relatively heavy but precise steering feel.
Market Reception & Comparison
The 420 SEC was generally well-received by automotive critics. It was praised for its luxurious interior, comfortable ride, and powerful engine. However, some critics noted that the automatic transmission dulled the driving experience compared to the manual options. Compared to the 300 SEC, the 420 SEC offered significantly more power and performance. Compared to the range-topping 560 SEC, the 420 SEC provided a good balance of performance and fuel economy, making it a more practical choice for some buyers. Fuel economy, while not a primary concern for buyers of this class of vehicle, was reasonable for a V8-powered coupe of its size and weight.
Legacy
The M116 engine, found in the 420 SEC, is known for its durability and longevity when properly maintained. While the K-Jetronic fuel injection system can require specialized knowledge for repairs, it is generally reliable. Today, the C126 420 SEC is a sought-after classic car, appreciated for its elegant styling, luxurious features, and robust engineering. Well-maintained examples command respectable prices in the used car market. The car represents a high point in Mercedes-Benz’s engineering and design history, and continues to provide a rewarding driving experience for enthusiasts.
