The Mercedes-Benz OM646.981 is a 2,987 cc, inline-five turbo-diesel engine produced between 2008 and 2013. It features common-rail direct injection, variable geometry turbocharging (VGT), and DOHC 20-valve configuration. In standard output, it delivers 140 kW (190 PS) and 440 Nm of torque, with applications across executive sedans and station wagons.
Fitted to models such as the W211 E-Class and W203 C-Class, the OM646.981 was engineered for balanced performance, fuel efficiency, and refinement. Emissions compliance was achieved via exhaust gas recirculation (EGR) and a diesel particulate filter (DPF), enabling Euro 5 certification for all production years in key markets.
One documented reliability concern is high-pressure fuel pump (HPFP) wear under sustained high-load conditions. This issue, highlighted in Mercedes-Benz Service Bulletin 20/2009, is linked to fuel contamination and marginal filtration in early builds. From 2010 onward, revised Bosch CP4-based fuel systems with improved filtration were implemented to enhance durability.
Production years 2008–2013 meet Euro 5 standards; certain export markets may have received enhanced DPF/SCR configurations (VCA UK Type Approval #VCA/EMS/5684).
The Mercedes-Benz OM646.981 is a 2,987 cc inline-five turbo-diesel engineered for mid-size and executive applications (2008–2013). It combines common-rail direct injection with a variable-geometry turbocharger to deliver responsive power and strong low-end torque. Designed to meet Euro 5 emissions standards, it balances everyday performance with long-distance efficiency.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,987 cc | |
| Fuel type | Diesel | |
| Configuration | Inline-5, DOHC, 20-valve | |
| Aspiration | Turbocharged | |
| Bore × stroke | 88.0 mm × 82.1 mm | |
| Power output | 140 kW (190 PS) @ 3,600 rpm | |
| Torque | 440 Nm @ 1,600–2,400 rpm | |
| Fuel system | Bosch CRS 3.0 common-rail (up to 1,800 bar) | |
| Emissions standard | Euro 5 (2008–2013) | |
| Compression ratio | 16.5:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Single variable-geometry turbo (Garrett GT1749V) | |
| Timing system | Dual chain (front-mounted, robust design) | |
| Oil type | MB 229.5 (SAE 5W-30) | |
| Dry weight | 195 kg |
The inline-five configuration provides smooth, linear power delivery ideal for highway cruising but demands strict adherence to 15,000 km oil change intervals using MB 229.5 specification oil to maintain turbo and HPFP longevity. Use of ultra-low-sulfur diesel (EN 590) is critical to prevent injector and fuel pump wear. Cold starts should be brief; prolonged idling increases EGR and DPF soot loading. Post-2010 models benefit from upgraded CP4 fuel pumps and enhanced filtration. EGR and DPF systems require periodic regeneration and cleaning to prevent limp mode. Timing chains are generally durable but inspection is recommended beyond 200,000 km.
Oil Specs: Requires MB 229.5 specification (Mercedes-Benz SIB 22/2007). Not compatible with ACEA A/B standards.
Emissions: Euro 5 applies to all 2008–2013 models. Export variants may include enhanced aftertreatment per VCA Type Approval #VCA/EMS/5684.
Power Ratings: Measured under DIN 70020. Output maintained across EU and North American variants (Mercedes-Benz TIS Doc. M13516).
Mercedes-Benz Technical Information System (TIS): Docs M12686, M13148, SIB 20/2009, SIB 22/2007
VCA Type Approval Database (VCA/EMS/5684)
ISO 1585:1996 Road vehicles — Test code for net power of internal combustion engines
The Mercedes-Benz OM646.981 was used across Mercedes-Benz's W211/W203 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-reinforced engine mounts in the W211 estate and revised cooling circuits in the W203-and from 2010 the updated W211 facelift adopted the OM646.982 variant with CP4 fuel system revisions, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front of the cylinder block near the timing cover (Mercedes-Benz TIS M12896). The 8th VIN digit indicates engine type ('6' for OM646 series). Pre-2010 models have silver valve covers with ribbed plastic covers; post-2010 units use black valve covers. Critical differentiation from OM646.982: Original .981 uses Bosch CP3 HPFP with circular fuel filter housing, while .982 uses CP4 with rectangular housing. Service parts require production date verification - fuel pumps and injectors before 06/2010 are not compatible with later units due to CP4 system integration (Mercedes-Benz SIB 20/2009).
The OM646.981's primary reliability risk is high-pressure fuel pump degradation, with elevated incidence in high-mileage and mixed-use conditions. Internal Mercedes quality reports from 2011 indicated a notable frequency of CP3 pump failures before 180,000 km in non-EU fuel markets, while UK DVSA data links EGR-related faults to urban-driven units. Extended idling and poor fuel quality increase HPFP and injector stress, making fuel filtration and oil interval adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (2008-2014) and UK DVSA failure statistics (2012-2020). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ OM646981.
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.
