The Mercedes-Benz 420 SEC, part of the C126 series facelift produced from August 1985 to September 1987, represented a luxurious and powerful grand touring coupe. Positioned as a mid-range offering within the C126 lineup – which also included the 380 SEC and the flagship 560 SEC – the 420 SEC aimed to balance performance with a more accessible price point than its higher-displacement sibling. It built upon the success of the initial C126 coupes launched in 1981, incorporating styling updates and refinements that solidified its status as a desirable luxury vehicle in both the North American and European markets. The “SEC” designation signified “S-Class Coupe,” emphasizing its connection to the prestigious S-Class sedan.
Technical Specifications
| Brand | Mercedes-Benz |
| Model | S-class |
| Generation | S-class Coupe (C126, facelift 1985) |
| Type (Engine) | 420 SEC V8 CAT (204 Hp) Automatic |
| Start of production | August, 1985 |
| End of production | September, 1987 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Coupe |
| Seats | 4 |
| Doors | 2 |
| Fuel consumption (urban) | 14.9 l/100 km (15.8 US mpg / 19 UK mpg) |
| Fuel consumption (extra urban) | 9.3 l/100 km (25.3 US mpg / 30.4 UK mpg) |
| Fuel Type | Petrol (Gasoline) |
| Acceleration 0 – 100 km/h | 8.7 sec |
| Acceleration 0 – 62 mph | 8.7 sec |
| Acceleration 0 – 60 mph | 8.3 sec |
| Maximum speed | 210 km/h (130.49 mph) |
| Weight-to-power ratio | 7.8 kg/Hp |
| Weight-to-torque ratio | 5.2 kg/Nm |
| Power | 204 Hp @ 5200 rpm |
| Torque | 310 Nm @ 3600 rpm (228.64 lb.-ft. @ 3600 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 | 9:1 |
| 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 capacity | 12.5 l (13.21 US qt | 11 UK qt) |
| Kerb Weight | 1600 kg (3527.4 lbs.) |
| Max. weight | 2120 kg (4673.8 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 | Rear wheel drive |
| Number of gears | 4 |
| Gearbox type | 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 |
| Tires size | 205/65 R15 |
| Wheel rims size | 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, operating two valves per cylinder. The M116 series was known for its robust construction and smooth operation. Bosch K-Jetronic fuel injection delivered precise fuel metering, contributing to both performance and relatively good fuel economy for the era. The catalytic converter (“CAT” in the model designation) was standard, reflecting increasingly stringent emissions regulations. The engine produced 204 horsepower at 5200 rpm and 310 Nm (228.64 lb-ft) of torque at 3600 rpm. Paired exclusively with a four-speed automatic transmission, the powertrain was designed for effortless cruising and refined acceleration. The transmission was a torque converter type, prioritizing smooth shifts over outright speed.
Driving Characteristics
The 420 SEC Automatic offered a distinctly different driving experience compared to its manual transmission counterparts or the higher-output 560 SEC. While not as overtly sporty, the 420 SEC provided ample power for comfortable highway cruising and confident overtaking. The automatic transmission, while smooth, did result in some power loss compared to a manual, and gear changes weren’t particularly quick by modern standards. The gear ratios were tuned for relaxed acceleration, prioritizing comfort over aggressive performance. The car felt substantial and planted on the road, thanks to its weight and well-tuned suspension. It wasn’t a nimble sports car, but a refined grand tourer capable of covering long distances with ease.
Equipment & Trim Levels
The 420 SEC came standard with a generous array of features befitting its luxury status. Leather upholstery was standard, along with power windows, power locks, and a sunroof. Climate control, a high-quality sound system, and cruise control were also included. Optional extras included upgraded leather, a premium sound system, and various wood trim options. The interior design was characterized by its elegant simplicity and high-quality materials. The dashboard layout was functional and driver-focused, with clear instrumentation and logically placed controls.
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 configuration provided a comfortable ride and good handling characteristics. The 420 SEC utilized ventilated disc brakes at the front and solid disc brakes at the rear. An Anti-lock Braking System (ABS) was standard, enhancing safety and control during hard braking. The steering was a recirculating ball system with hydraulic power assistance, providing a good balance of feel and ease of use. The car rode on 7J x 15 inch wheels with 205/65 R15 tires.
Market Reception & Comparison
The 420 SEC was generally well-received by automotive critics. It was praised for its luxurious interior, comfortable ride, and refined engine. However, some critics noted that the automatic transmission dulled the engine’s performance somewhat. Compared to the 380 SEC, the 420 SEC offered a noticeable increase in power and performance. Compared to the 560 SEC, it provided a more affordable entry point into the C126 coupe range, albeit with slightly less power. Fuel economy, while reasonable for a V8 of this era, was still relatively high – around 15.8 US mpg in the city and 25.3 US mpg on the highway.
Legacy
The Mercedes-Benz 420 SEC has become a sought-after classic car among enthusiasts. The M116 engine, when properly maintained, is known for its durability and longevity. However, like all classic Mercedes-Benzes, the 420 SEC requires regular maintenance to keep it in good running order. Parts availability can be a challenge, but a dedicated network of suppliers caters to the classic Mercedes-Benz community. Today, the 420 SEC represents a bygone era of automotive luxury and engineering excellence, offering a unique and rewarding driving experience for those willing to invest in its upkeep.
