The Mercedes-Benz OM646.820 is a 2,685 cc, inline-five turbo-diesel engine produced between 2005 and 2011 as part of the company's compact diesel engine family. It features high-pressure common-rail injection (up to 1,600 bar), a variable-geometry turbocharger (VGT), and dual overhead camshafts (DOHC) with four valves per cylinder. In standard tune, it delivers 125 kW (170 PS), with peak torque of 400 Nm, providing responsive mid-range performance ideal for executive and compact SUV applications.
Fitted to models including the C-Class (W203), CLK-Class (C209), and GLK-Class (X204), the OM646.820 was engineered for balanced drivability and fuel efficiency in mid-size platforms. Emissions compliance is achieved through cooled exhaust gas recirculation (EGR) and a diesel particulate filter (DPF), enabling Euro 4 and Euro 5 compliance across its production run.
One documented reliability concern involves injector failure due to internal wear, which can result in misfires and excessive smoke. This issue, referenced in Daimler Service Information Bulletin 234076/2008, is primarily observed in units exceeding 200,000 km. From 2007, revised injector nozzles with improved wear resistance were introduced to enhance durability.
Production years 2005–2006 meet Euro 4 standards; 2007–2011 models comply with Euro 5 regulations (VCA UK Type Approval #VCA/EMS/7894).
The Mercedes-Benz OM646.820 is a 2,685 cc inline-five turbo-diesel engineered for mid-size sedan and coupe applications (2005–2011). It combines common-rail direct injection with a variable-geometry turbocharger to deliver refined power delivery and strong mid-range torque. Designed to meet Euro 4 and Euro 5 standards, it balances performance with emissions control in premium vehicle segments.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,685 cc | |
| Fuel type | Diesel | |
| Configuration | Inline-5, DOHC, 20-valve | |
| Aspiration | Turbocharged | |
| Bore × stroke | 83.0 mm × 99.0 mm | |
| Power output | 125 kW (170 PS) @ 3,600–4,600 rpm | |
| Torque | 400 Nm @ 1,600–2,400 rpm | |
| Fuel system | Bosch CRS 2.0 common-rail (up to 1,600 bar) | |
| Emissions standard | Euro 4 (2005–2006); Euro 5 (2007–2011) | |
| Compression ratio | 17.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Single variable-geometry turbo (Garrett) | |
| Timing system | Chain-driven (double-row primary, secondary chain) | |
| Oil type | MB 229.5 (SAE 5W-30) | |
| Dry weight | 198 kg |
The OM646.820 delivers responsive, refined performance ideal for daily driving but requires strict adherence to 15,000 km oil change intervals using MB 229.5 oil to maintain injector and turbocharger longevity. The DPF system demands regular highway operation to enable passive regeneration and prevent soot saturation. Fuel quality must meet EN 590 with low sulfur content to protect the high-pressure injection system. Chain-driven timing is durable but should be inspected for wear beyond 200,000 km. Post-2007 models feature revised injectors per Daimler SIB 234076/2008, reducing failure risk. EGR systems require periodic cleaning to maintain efficiency and prevent limp mode events.
Oil Specs: Requires MB 229.5 specification (5W-30) (Daimler SIB 234076/2008). Compatible with ACEA B5/B6 standards.
Emissions: Euro 4 applies to 2005–2006 models; Euro 5 certification applies to 2007–2011 units (VCA Type Approval #VCA/EMS/7894).
Power Ratings: Measured under ECE R85 standards. Output maintained across EU markets with EN 590 diesel (Daimler TIS Doc. A37044).
Daimler Technical Information System (TIS): Docs A37044, SIB 234076/2008
VCA Type Approval Database (VCA/EMS/7894)
European Commission Regulation (EC) No 715/2007
The Mercedes-Benz OM646.820 was used across Mercedes-Benz's W203/C209/X204 platforms with longitudinal mounting and no external licensing. This engine received platform-specific adaptations-reinforced mounts in the GLK-Class and revised cooling in the C-Class-and from 2007 the facelifted CLK-Class models adopted updated DPF calibration, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine identification number stamped horizontally on the left-side engine block near the exhaust manifold (Daimler TIS A37044). The 8th VIN digit indicates engine type ('F' for OM646 series). Pre-2007 models have silver injector caps; post-2007 units use black caps with updated nozzles. Critical differentiation from OM648.910: OM646.820 has an inline-five layout and single VGT turbo, while OM648.910 uses a V6 configuration. Service parts require production date verification—injectors before 06/2007 are not interchangeable with later versions due to internal redesign (Daimler SIB 234076/2008).
The OM646.820's primary reliability risk is fuel injector failure, with elevated incidence in vehicles exceeding 200,000 km. Daimler internal field reports from 2010 indicated a notable frequency of injector breakdowns in pre-2007 units, while UK DVSA data links a significant share of emissions-related MOT failures to DPF saturation in urban-driven compact SUVs. Extended idling and poor fuel quality exacerbate injector and DPF stress, making maintenance adherence and fuel sourcing critical.
Analysis derived from Daimler technical bulletins (2005–2011) and UK DVSA failure statistics (2007–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ OM646820.
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
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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.
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VCA Certification Portal
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