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,…
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 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.
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.
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The OM646.981 offers smooth performance and strong torque, but early models (2008-2009) are prone to HPFP failures, especially with poor fuel quality. Later revisions (post-2010) with CP4 pumps improved reliability. Well-maintained units with proper oil changes and quality diesel can exceed 250,000 km. Using MB 229.5 oil and adhering to service intervals is essential for longevity.
Key issues include high-pressure fuel pump failure, EGR valve and cooler clogging, turbo actuator sticking, and oil leaks from valve cover gaskets. These are documented in Mercedes-Benz service bulletins. Fuel quality significantly impacts HPFP and injector life. Regular EGR cleaning and use of OEM-spec oil help mitigate common failures.
This 3.0L inline-five diesel was used in the W211 E-Class (E300 CDI), S211 E-Class Estate (E300 CDI), and W203 C-Class (C300 CDI) from 2008 to 2013. It was phased out in favor of the OM642 V6 in most applications. No cross-manufacturer usage is documented for this variant.
Yes, the OM646.981 responds well to ECU remapping. Stage 1 tunes typically add +30-40 kW safely, as the stock turbo and internals handle increased torque. Further gains require upgraded cooling, exhaust, and fuel system components. Tuning should be performed by specialists familiar with Bosch CRS 3.0 systems to avoid fuel pump strain.
In combined driving, the OM646.981 achieves approximately 7.5–8.2 L/100km (38–34 mpg UK). Highway driving can yield as low as 6.3 L/100km (~45 mpg UK), while city use may exceed 9.0 L/100km (~31 mpg UK). Real-world consumption depends on vehicle weight and driving style, but it remains competitive for a 3.0L diesel inline-five.
Yes. The OM646 series is an interference engine. If the timing chain fails or skips, pistons will contact open valves, resulting in catastrophic internal damage. While the front-mounted dual chain is robust, inspection beyond 200,000 km is advised. Any abnormal noise from the timing cover warrants immediate investigation.
Mercedes-Benz specifies SAE 5W-30 oil meeting MB 229.5 standard. This low-SAPS formulation is essential for DPF and turbo longevity. Oil changes should occur every 15,000 km or annually. Using non-compliant oil can lead to CCV clogging, increased oil consumption, and aftertreatment damage.
Comprehensive technical documentation and regulatory references
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MERCEDES-BENZ Official Site
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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
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