The Mercedes-Benz OM646.821 is a 2,987 cc, inline-six turbo-diesel engine produced between 2006 and 2011. 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 140 kW (190 PS) and 440 Nm of torque, with higher-output variants reaching 165 kW (224 PS), offering strong pulling performance and smooth operation for premium applications.
Fitted to the W211 E-Class, W221 S-Class, and W164 ML-Class, the OM646.821 was designed for long-distance comfort, driving refinement, and responsive performance in heavy vehicles. Emissions compliance was achieved through cooled exhaust gas recirculation (EGR), a diesel particulate filter (DPF), and oxidation catalyst, enabling Euro IV certification across its production run. Its design emphasizes NVH reduction and thermal durability under sustained load.
One documented reliability concern is premature high-pressure fuel pump wear, particularly in early-series units (2006–2008). Highlighted in Daimler Service Information Bulletin 20-06-008, the issue is linked to marginal fuel filtration and sensitivity to low-lubricity diesel. From 2009, revised pump calibration and updated fuel filter specifications (A 001 475 52 03) were implemented to improve longevity.
Production years 2006–2009 meet Euro IV standards; 2010–2011 models meet Euro V (VCA UK Type Approval #VCA/DIESEL/OM646).
The Mercedes-Benz OM646.821 is a 2,987 cc inline-six turbo-diesel engineered for executive and luxury SUV platforms (2006–2011). 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 IV and later 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 | 140–165 kW (190–224 PS) | |
| Torque | 440–600 Nm @ 1,600–2,400 rpm | |
| Fuel system | Bosch CRS 2.0 common-rail (1,800 bar max) | |
| Emissions standard | Euro IV (2006–2009); Euro V (2010–2011) | |
| 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 | 235 kg |
The OM646.821 delivers strong low-RPM torque ideal for luxury and towing applications but requires strict adherence to fuel quality standards to prevent high-pressure pump and injector wear. MB 229.5 or MB 229.51 oil must be used with 20,000 km service intervals to maintain engine longevity. Ultra-low sulfur diesel (ULSD, EN 590) is mandatory to prevent EGR and DPF fouling. The dual-row timing chain system demands timely replacement per manufacturer schedule—failure to service can result in catastrophic engine damage. Early units (pre-2009) should have pump recalibration per Daimler SIB 20 06 008 to mitigate premature failure. Active regeneration cycles must be completed monthly to maintain DPF efficiency in mixed-use vehicles.
Oil Specs: Requires MB 229.5 or MB 229.51 specification (Daimler SIB 20 06 008). Compatible with ACEA B5/B6 standards.
Emissions: Euro IV applies to 2006–2009 models; Euro V applies to 2010–2011 (VCA Type Approval #VCA/DIESEL/OM646).
Power Ratings: Measured under ISO 1585. Higher outputs (224 PS) require AdBlue-equipped Euro V variants (2010+).
Daimler Technical Information System (TIS): Docs M128005, M128006, SIB 20 06 008
VCA Type Approval Database (VCA/DIESEL/OM646)
ISO 1585: Road vehicles — Engine test code — Net power
The Mercedes-Benz OM646.821 was used across Mercedes-Benz's W211, W221, and W164 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-reinforced mounts in the W221 and integrated AdBlue dosing in the W164-and from 2011 the Euro V-compliant OM642LA replaced earlier variants, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine ID plate mounted on the right-side cylinder block near the oil filter housing (Daimler TIS M128009). The 7th digit of the VIN indicates engine type ('L' for OM646 series). Pre-2009 units have a Bosch CP3.3 high-pressure pump; post-2009 revisions use CP3.4 with dual filtration. Critical differentiation from OM648: OM646.821 is a 3.0L inline-six with 88 mm bore and uses a Garrett VGT turbo, while OM648 is a 5.0L V8. Service parts require chassis number verification—fuel pumps for pre-2009 models are incompatible with later units due to calibration differences (Daimler SIB 20 06 008).
The OM646.821'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 2009 indicated over 13% of pre-2008 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 (2006-2011) and UK DVSA failure statistics (2011-2019). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ OM646821.
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