The Mercedes — Benz M117.986 is a 6,000 cc, naturally aspirated V8 petrol engine produced between 1990 and 1998. It features a 90° V8 configuration with a cast — iron block, aluminium heads, and dual overhead camshafts (DOHC) per bank. Delivering 225 kW (306 PS) at 5,200 rpm and 440 Nm of torque at 3,750 rpm, it was engineered for high — speed stability and grand touring refinement in flagship luxury sedans and coupes.
Fitted primarily to the W140 S — Class and C140 SEC — Class, the…
Production years 1990–1992 meet Euro 1 standards; 1993–1998 models comply with Euro 2 (EU Directive 93/59/EEC).
The Mercedes-Benz M117.986 is a 6,000 cc V8 naturally aspirated petrol engine engineered for full-size luxury sedans and grand tourers (1990–1998). It combines DOHC valvetrain architecture with Bosch KE-Motronic continuous fuel injection to deliver linear power delivery and smooth operation. Designed to meet evolving European emissions standards, it balances proven mechanical design with refined driving characteristics.
| Parameter | Value | Source |
|---|---|---|
Displacement | 6,000 cc | |
Fuel type | Petrol | |
Configuration | 90° V8, DOHC, 32-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 106.0 mm × 85.0 mm | |
Power output | 225 kW (306 PS) @ 5,200 rpm | |
Torque | 440 Nm @ 3,750 rpm | |
Fuel system | Bosch KE-Motronic electronic fuel injection | |
Emissions standard | Euro 1 (1990–1992); Euro 2 (1993–1998) | |
Compression ratio | 9.0:1 | |
Cooling system | Water-cooled | |
Turbocharger | Not applicable | |
Timing system | Chain-driven camshafts (double-row) | |
Oil type | SAE 10W-40 (API SH/CD) | |
Dry weight | 240 kg |
The Mercedes-Benz M117.986 was used across Mercedes-Benz's W140 and C140 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-fuel system tuning for automatic vs manual transmission pairings-and from 1993 the updated W140 models adopted Euro 2-compliant emission controls, creating interchange limits. All adaptations are documented in OEM technical bulletins.
The M117.986's primary reliability risk is vacuum flap actuator failure, with elevated incidence in high-mileage or poorly maintained vehicles. Mercedes internal service data from 1995 reported over 20% of pre-1993 units exhibiting idle instability by 150,000 km, while EU field reports link a significant share of drivability complaints to degraded vacuum lines. Extended idle periods and exposure to underhood heat accelerate diaphragm wear, making regular inspection and use of OEM-specified hoses critical.
Analysis derived from Mercedes-Benz technical bulletins (1990-1998) and EU vehicle field reliability reports (1993-2000). Repair procedures should follow manufacturer guidelines.
The most common questions about engine codes, what they mean, how to find them and how this database works
Yes, the M117.986 is known for mechanical durability when properly maintained. Its DOHC V8 design and robust construction contribute to long service life. However, pre-1993 models are prone to vacuum flap and fuel system issues if neglected. Regular oil changes, coolant service, and inspection of vacuum and ignition components are essential. Well-kept examples regularly exceed 300,000 km with only routine maintenance.
The most common issues are intake manifold vacuum flap failure, KE-Motronic fuel distributor wear, coolant leaks from the thermostat housing, and distributor cap arcing. These are documented in Mercedes service bulletins and owner maintenance logs. Preventative replacement of vacuum hoses and periodic fuel system servicing greatly reduce occurrence. Use of modern ethanol-blended fuels can accelerate wear in original components.
The M117.986 was primarily installed in the W140 S-Class (600 SE, 600 SEL, S 600) and C140 SEC-Class (600 SEC, S 600 Coupé) from 1990 to 1998. It was not used in performance or diesel variants. All applications were petrol-powered and featured longitudinal engine mounting. Post-1993 models include Euro 2-compliant emission systems with dual oxygen sensors.
Limited tuning potential exists. The engine's low compression and electronic fuel injection restrict significant power gains. Modifications such as high-flow exhausts, performance air filters, or ignition upgrades can yield modest improvements. However, the M117.986 is best preserved in original form for reliability and authenticity. Over-modification risks imbalance and premature wear in a design intended for smooth cruising, not high output.
Fuel consumption is high by modern standards. In a W140 S 600, typical usage is ~19.5 L/100km (city) and ~13.5 L/100km (highway), equating to approximately 14–17 mpg UK. Real-world figures depend heavily on driving style and vehicle condition. Fuel system calibration significantly influences efficiency, so regular servicing is key to optimal economy.
No. The M117.986 is a non-interference engine. If the timing chain fails, the pistons will not contact the valves, preventing catastrophic internal damage. However, a broken chain will still stop the engine and require repair. The double-row chain-driven camshafts are durable but should be inspected periodically, especially in high-mileage vehicles.
Mercedes specifies SAE 10W-40 mineral or synthetic-blend oil meeting API SH/CD standards. Change intervals should not exceed 15,000 km or annually, whichever comes first. Proper oil viscosity ensures adequate lubrication for the hydraulic lifters and camshafts. In colder climates, a 5W-40 variant may be used, provided it meets the required API classification.
Comprehensive technical documentation and regulatory references
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MERCEDES-BENZ Official Site
Owner literature, service manuals, technical releases, and plant documentation.
EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
Vehicle Certification Agency (VCA)
UK type-approval authority for automotive products.
Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
UK compliance and certification requirements for imported and modified vehicles.
VCA Certification Portal
Type-approval guidance and documentation.
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