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 M117.986 was designed to provide effortless power delivery and long-distance cruising capability. It met Euro 2 emissions standards through precision electronic fuel injection (Bosch KE-Motronic) and exhaust gas recirculation (EGR), with catalytic converter integration standard across all markets from launch.
One documented service concern involves degradation of the intake manifold vacuum flaps, which can lead to unstable idle and hesitation under light load. This issue, referenced in Mercedes Technical Service Bulletin 01.03.178, is typically caused by cracked diaphragms or blocked vacuum lines. Later production units incorporated revised vacuum actuators and updated flap linkage to improve long-term reliability.
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 M117.986 provides smooth, refined V8 performance ideal for grand touring but requires consistent maintenance to preserve fuel and vacuum system integrity. Use of SAE 10W-40 oil meeting API SH/CD specifications is essential for camshaft and lifter lubrication. Vacuum-operated intake flaps should be inspected every 30,000 km to prevent idle instability. Fuel distributor and warm-up regulator servicing every 60,000 km maintains optimal air-fuel metering. Original KE-Motronic systems are sensitive to fuel quality; use of high-octane petrol (RON 98) prevents knock and maintains long-term injector and accumulator performance. Coolant system integrity is critical—replace hoses and thermostat every 90,000 km to prevent overheating.
Oil Specs: Requires SAE 10W-40 API SH/CD specification (Mercedes SIB 01.03.178). Supersedes earlier SF/CC standards.
Emissions: Euro 2 certification applies to post-1993 models only (EU Directive 93/59/EEC). Pre-1993 units comply with Euro 1 under Directive 88/77/EEC.
Power Ratings: Measured under DIN 70020 standards. Output consistent across all markets with catalytic converter.
Mercedes-Benz Technical Information System (TIS): Docs A11772, M117-006, SIB 01.03.178
European Commission: Directive 93/59/EEC
SAE International: DIN 70020 Engine Power Measurement Standard
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.
Locate the engine code stamped vertically on the front face of the right cylinder bank, near the timing cover (Mercedes TIS A11782). The 7th and 8th digits of the VIN indicate engine type ('17' for M117 series). Pre-1993 models feature simpler EGR routing; post-1993 Euro 2 variants have revised air injection and secondary oxygen sensor placement. Critical differentiation from M117.960: M117.986 has a longer stroke (85.0 mm vs 78.7 mm) and larger displacement. Service parts require VIN and production date verification—intake manifold flaps and vacuum actuators for pre-1993 models are not compatible with Euro 2 variants due to calibration differences (Mercedes SIB 01.03.178).
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.
Find answers to most commonly asked questions about MERCEDES-BENZ M117986.
Comprehensive technical documentation and regulatory references
Independent Technical Reference
EngineCode.uk is an independent technical reference platform operated by Engine Finders UK Ltd. We are not affiliated with MERCEDES-BENZ or any other manufacturer. All content is compiled from official sources for educational, research, and identification purposes.
Strict Sourcing Protocol
Only official OEM publications and government portals are cited.
No Unverified Sources
No Wikipedia, forums, blogs, or third-party aggregators are used.
Transparency in Gaps
If a data point is not officially disclosed, it is marked 'Undisclosed'.
Regulatory Stability
EU regulations are referenced using CELEX identifiers for long-term stability.
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.
Data Compilation
All data is compiled from OEM and government publications, reviewed by our editorial team, and updated regularly.
Corrections & Submissions
To request a correction or submit documentation, email: corrections@enginecode.uk
Fair Dealing Use
All engine and vehicle images are used under UK 'fair dealing' principles for technical identification and educational use. Rights remain with their respective owners.
Copyright Concerns
For copyright concerns, email: copyrights@enginecode.uk
GDPR Compliance
EngineCode.uk complies with UK GDPR. We do not collect personal data unless explicitly provided.
Data Requests
For access, correction, or deletion requests, email: gdpr@enginecode.uk
Trademark Notice
All trademarks, logos, and engine codes are the property of their respective owners. Use on this site is strictly for reference and identification.
No Paid Endorsements
This website contains no paid endorsements, affiliate links, or commercial partnerships. We do not sell parts or services.
Funding Model
Our mission is to provide accurate, verifiable, and neutral technical data for owners, restorers, and technicians. This site is self-funded.
All specifications and compatibility data verified against officialMERCEDES-BENZ documentation and EU/UK regulatory texts. Where official data is unavailable, entries are marked “Undisclosed“ .
All external links open in new tabs. Please verify current availability of resources.
