The Mercedes — Benz OM646.985 is a 2,987 cc, inline — six turbo — diesel engine produced between 2008 and 2013. It was engineered as a refined, high — torque powerplant for executive sedans and luxury SUVs, featuring common — rail direct injection, variable geometry turbocharging (VGT), and dual overhead camshafts (DOHC). In standard output, it delivered 150 kW (204 PS) and 540 Nm of torque, with higher — output variants reaching 165 kW (224 PS), offering strong pulling perf…
Production years 2008–2013 meet Euro V standards (VCA UK Type Approval #VCA/DIESEL/OM646LA).
The Mercedes-Benz OM646.985 is a 2,987 cc inline-six turbo-diesel engineered for executive and luxury SUV platforms (2008–2013). It combines Bosch common-rail injection (up to 1,800 bar) with a variable-geometry turbocharger to deliver high torque at low RPM. Designed to meet Euro V emissions standards, it balances premium driving refinement with regulated environmental performance.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,987 cc | |
Fuel type | Diesel | |
Configuration | Inline-6, DOHC, 24-valve | |
Aspiration | Turbocharged with VGT | |
Bore × stroke | 88.0 mm × 82.1 mm | |
Power output | 150–165 kW (204–224 PS) | |
Torque | 540–620 Nm @ 1,600–2,400 rpm | |
Fuel system | Bosch CRS 2.0 common-rail (1,800 bar max) | |
Emissions standard | Euro V | |
Compression ratio | 16.5:1 | |
Cooling system | Water-cooled | |
Turbocharger | Garrett GT1752V VGT | |
Timing system | Chain-driven (dual-row, service-interval critical) | |
Oil type | MB 229.5 or MB 229.51 | |
Dry weight | 238 kg |
The Mercedes-Benz OM646.985 was used across Mercedes-Benz's W212, W221, and W164 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-integrated AdBlue dosing in the W164 and revised EGR routing in the W212-and from 2013 was succeeded by the OM654 for modular diesel architecture, creating interchange limits. All adaptations are documented in OEM technical bulletins.
The OM646.985's primary reliability risk is high-pressure fuel pump wear in early builds, with elevated incidence in regions with inconsistent fuel quality. Daimler internal reports from 2010 indicated over 10% of pre-2010 units required pump replacement before 250,000 km, while VCA field data shows Euro V DPF systems in mixed-use fleets require cleaning every 70,000–90,000 km. Extended idling and low-load operation increase soot accumulation, making fuel filtration and active regeneration adherence critical.
Analysis derived from Daimler technical bulletins (2008-2013) and UK DVSA failure statistics (2013-2021). Repair procedures should follow manufacturer guidelines.
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The OM646.985 is mechanically robust with a refined inline-six design and strong torque delivery. However, early models (2008–2010) are prone to high-pressure fuel pump wear if operated with poor-quality diesel. Later revisions (post-2011) with CP3.4 pumps and updated calibration show improved reliability. Consistent use of MB-approved oil and ULSD fuel, along with adherence to 20,000 km service intervals, enables long-term operation beyond 350,000 km.
Primary issues include high-pressure fuel pump wear (especially pre-2011 CP3.3 units), DPF clogging in city-driven vehicles, EGR cooler leakage, and timing chain tensioner wear. These are documented in Daimler service bulletins and field reports. Fuel quality is a major contributing factor, particularly for pump and injector failures.
The OM646.985 was used in several Mercedes-Benz luxury models: the E-Class (W212) E 350 CDI (2009–2013), S-Class (W221) S 350 CDI (2008–2013), and ML-Class (W164) ML 350 CDI (2008–2011). It was not used in passenger cars or licensed to other manufacturers. All applications were Euro V-compliant executive vehicles.
Yes. The OM646.985 responds well to ECU remapping, typically gaining +30–50 kW. Stock components—particularly the CP3.4 pump and Garrett turbo—can support moderate tuning. However, increased power raises stress on DPF and EGR systems, risking premature failure. Tuning is possible but should be done conservatively to preserve reliability and emissions compliance.
In the E 350 CDI (W212), typical fuel consumption is ~8.8 L/100km (urban) and ~6.2 L/100km (highway), depending on load and driving conditions. Real-world economy ranges from 7.0–9.5 L/100km in mixed service. The engine's efficiency is optimized for steady cruising, not frequent stop-start driving.
Yes. The OM646.985 is an interference engine, meaning piston-to-valve contact occurs if timing is lost. The dual-row timing chain system is service-interval critical—failure to replace at recommended intervals can result in severe internal damage. Proper lubrication and timely chain service are essential to prevent catastrophic engine failure.
Mercedes-Benz specifies MB 229.5 or MB 229.51 synthetic oil (5W-40 or 0W-40) for the OM646.985. Change intervals are up to 20,000 km under normal conditions. Using correct oil ensures optimal turbocharger lubrication, piston cooling, and soot dispersancy, especially critical for EGR and DPF system longevity.
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.
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