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 execut…
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 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.
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.
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The OM646.820 is generally robust with strong build quality, but pre-2007 models are prone to injector failure beyond 200,000 km, especially with poor fuel quality. Later revisions (post-2007) improved nozzle durability. When maintained with correct MB 229.5 oil and regular DPF regeneration, these engines can reliably exceed 250,000 km in regular service.
Key issues include fuel injector failure (especially pre-2007), DPF saturation from short trips, turbo actuator sticking, and timing chain guide wear. These are documented in Daimler service bulletins and field reports. Injector faults and regeneration failures are the most frequent causes of major repair.
This 2.7L diesel is used in the C-Class (W203), CLK-Class (C209), and GLK-Class (X204) models. It powers C 270 CDI, CLK 270 CDI, and GLK 270 CDI variants produced between 2005 and 2011. It meets Euro 4 (2005–2006) and Euro 5 (2007–2011) standards with DPF for emissions control.
Yes, the OM646.820 responds well to ECU remapping. Stage 1 tunes typically yield +25–40 kW safely by optimizing boost and injection timing. However, over-tuning can strain the single VGT turbo and fuel system. Supporting modifications like upgraded intercoolers and fuel pressure regulators are recommended for higher stages to maintain reliability in performance applications.
In real-world use, the OM646.820 achieves approximately 7.5–9.0 L/100km (38–31 mpg UK) in the C-Class or CLK-Class, and 8.5–10.5 L/100km (33–27 mpg UK) in the GLK-Class. Highway driving can yield up to 40 mpg UK. Consumption depends heavily on load, driving style, and DPF regeneration frequency.
Yes. The OM646.820 is an interference engine. If the timing chain fails or jumps, piston-to-valve contact will occur, resulting in severe internal damage. Regular inspection of chain guides and tensioners is essential, especially on high-mileage engines, to prevent catastrophic failure.
Mercedes specifies MB 229.5 (SAE 5W-30) synthetic oil. This formulation is critical for protecting the injectors, turbocharger, and DPF. Oil must be changed every 15,000 km or annually to prevent sludge buildup and maintain long-term reliability in premium applications.
Comprehensive technical documentation and regulatory references
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EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
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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
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