The Mercedes-Benz OM 646.812 is a 3,996 cc, V8 twin-turbo diesel engine produced between 2006 and 2011. It features common-rail direct injection, sequential twin variable-geometry turbochargers (VGT), and a DOHC 32-valve valvetrain, delivering high torque and smooth performance for luxury and performance applications. In standard tune, it produced 210 kW (286 PS) at 3,600 rpm and 730 Nm of torque between 2,000–2,600 rpm.
Fitted to models such as the W221 S420 CDI, W216 CLS420 CDI, and W164 GL420 CDI, the OM 646.812 was engineered for refined driving dynamics and strong mid-range pull. Emissions compliance was achieved through exhaust gas recirculation (EGR), a diesel particulate filter (DPF), and precise common-rail fuel metering, allowing most units to meet Euro 4 standards, with later builds achieving Euro 5 depending on market.
One documented concern is high-pressure fuel pump (HPFP) wear or failure, particularly under high-load operation or with prolonged use of substandard diesel fuel. This issue, highlighted in Daimler Service Information Bulletin 70.00-P-1007-8, is linked to contamination or lubricity issues in ultra-low-sulfur diesel (ULSD). From 2009, revised pump internals and updated fuel filtration were introduced to improve durability.
Production years 2006–2008 meet Euro 4 standards; 2009–2011 models comply with Euro 5 depending on market (VCA UK Type Approval #VCA/EMS/9012).
The Mercedes-Benz OM 646.812 is a 3,996 cc V8 twin-turbo diesel engineered for executive and SUV platforms (2006–2011). It combines common-rail direct injection with sequential twin-turbocharging to deliver strong mid-range torque and refined performance. Designed to meet Euro 4 and Euro 5 standards, it balances power delivery with emissions control.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 3,996 cc | |
| Fuel type | Diesel | |
| Configuration | V8, DOHC, 32-valve | |
| Aspiration | Twin-turbocharged (sequential), intercooled | |
| Bore × stroke | 88.0 mm × 82.1 mm | |
| Power output | 210 kW (286 PS) @ 3,600 rpm | |
| Torque | 730 Nm @ 2,000–2,600 rpm | |
| Fuel system | Bosch CRS 3-18 common-rail (up to 1,800 bar) | |
| Emissions standard | Euro 4 (pre-2009); Euro 5 (2009–2011, market-dependent) | |
| Compression ratio | 16.5:1 | |
| Cooling system | Water-cooled, electric thermostat | |
| Turbocharger | Sequential twin variable-geometry turbochargers | |
| Timing system | Dual-row timing chain (DOHC) | |
| Oil type | MB 229.51 (SAE 5W-30) or MB 229.5 (SAE 5W-40) | |
| Dry weight | 238 kg |
The sequential twin-turbo setup provides strong, lag-free torque delivery ideal for heavy luxury sedans and SUVs but requires strict adherence to 15,000 km oil change intervals to protect the high-pressure fuel pump and turbo actuators. MB 229.51 or 229.5 oil is critical due to its specific formulation for diesel particulate filter compatibility and fuel system protection. Cold-start idling should be limited to reduce EGR soot accumulation. The Bosch CRS 3-18 fuel pump demands ultra-low-sulfur diesel (ULSD) meeting EN 590 standards to prevent premature wear. Post-2009 models feature improved fuel filtration; pre-2009 units benefit from upgraded inline filters. EGR and DPF systems require periodic cleaning to maintain emissions compliance and prevent regeneration-related limp mode.
Oil Specs: Requires MB 229.51 (5W-30) or MB 229.5 (5W-40) specification (Daimler Service Manual W221/W216). Ensures DPF regeneration and fuel pump longevity.
Emissions: Euro 4 certification applies to pre-2009 models only (VCA Type Approval #VCA/EMS/9012). Euro 5 compliance varies by market for 2009–2011 models.
Power Ratings: Measured under DIN 70020 standards. Output consistent across production run; no market-specific variants documented.
Daimler Technical Information System (TIS): Docs 646.00-2001, 070.00-3100, SIB 70.00-P-1007-8
VCA Type Approval Database (VCA/EMS/9012)
ISO 1585:1976 Road vehicles — Engine test code — Net power
The Mercedes-Benz OM 646.812 was used across Mercedes-Benz's W221/W216/W164 platforms with longitudinal mounting and no external licensing. This engine received platform-specific adaptations-reinforced mounts in the W164 SUV and revised cooling routing in the W221 limousine-and from 2009 the W216 received updated fuel filtration, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front-facing side of the cylinder block, just below the intake manifold (Daimler TIS 646.812-0100). The 9th digit of the VIN identifies the engine type ('D' for diesel). Pre-2009 units have a single-stage fuel filter housing; post-2009 models use a dual-stage design with water separator. Critical differentiation from OM 642.886: OM 646.812 has a larger displacement (3,996 cc vs 3,009 cc), V8 configuration, and higher torque output (730 Nm vs 620 Nm). Service parts require chassis number verification—cooling manifolds for W221 models differ from W216 due to routing revisions (Daimler SIB 70.00-P-1007-8).
The OM 646.812's primary reliability risk is high-pressure fuel pump wear under sustained load or poor fuel quality, with elevated incidence in long-distance and high-mileage applications. Daimler internal field reports from 2010 noted increased HPFP failures in W221 S420 CDI units operating in regions with variable diesel quality, while VCA historical archives indicate fuel contamination as a leading cause of premature pump wear in preserved examples. Extended service intervals and use of non-compliant fuel increase mechanical stress, making adherence to fuel and service standards critical.
Analysis derived from Daimler technical bulletins (2006-2011) and UK DVSA failure statistics (2010-2020). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ OM646812.
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