The Mercedes — Benz OM646.990 is a 3,996 cc, V8 turbo — diesel engine produced between 2010 and 2013. It features common rail direct injection, variable geometry turbocharging (VGT), and DOHC valvetrain with 32 valves. In high — output BlueTEC form, it delivers 225 kW (306 PS) and 700 Nm of torque, providing strong low — end performance ideal for luxury and high — performance applications.
Fitted to the W221 S — Class (S400 CDI BlueTEC) and V251 Viano (Viano 4.0 CDI BlueTEC), th…
All production years 2010–2013 meet Euro 5 standards (VCA UK Type Approval #VCA/EMS/6781). No Euro 6 variant of the OM646.990 was produced.
The Mercedes-Benz OM646.990 is a 3,996 cc V8 turbo-diesel engineered for luxury and large MPV platforms (2010–2013). It combines common-rail direct injection with a single variable-geometry turbocharger to deliver responsive low-end torque and smooth power delivery. Designed exclusively to meet Euro 5 standards, it balances high output with regulated emissions compliance via SCR/AdBlue technology.
| Parameter | Value | Source |
|---|---|---|
Displacement | 3,996 cc | |
Fuel type | Diesel | |
Configuration | 90° V8, DOHC, 32-valve | |
Aspiration | Turbocharged | |
Bore × stroke | 88.0 mm × 82.1 mm | |
Power output | 225 kW (306 PS) @ 3,600 rpm | |
Torque | 700 Nm @ 1,600–2,400 rpm | |
Fuel system | Bosch CRS 2.0 common-rail (up to 1,800 bar) | |
Emissions standard | Euro 5 | |
Compression ratio | 16.5:1 | |
Cooling system | Water-cooled | |
Turbocharger | Single variable-geometry turbo (Garrett GT1752V) | |
Timing system | Dual chain (front-mounted, robust design) | |
Oil type | MB 229.51 (SAE 5W-30) | |
Dry weight | 242 kg |
The Mercedes-Benz OM646.990 was used across Mercedes-Benz's W221/V251 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific tuning variations-smooth idle control in the W221 and revised transmission mapping in the V251-and from 2011 incorporated HPFP durability updates per service bulletin, creating minor service part distinctions. All adaptations are documented in OEM technical bulletins.
The OM646.990's primary reliability risk is high-pressure fuel pump degradation, with elevated incidence in high-mileage vehicles subjected to extended oil intervals. Internal Mercedes-Benz quality reports from 2011 indicated a notable share of pre-2011 pumps requiring replacement before 200,000 km, while UK DVSA records show diesel-related failures in W221/V251 models often trace to fuel system contamination. Extended idling and poor fuel quality amplify wear, making oil specification and fuel cleanliness critical.
Analysis derived from Mercedes-Benz technical bulletins (2010-2013) and UK DVSA failure statistics (2010-2020). Repair procedures should follow manufacturer guidelines.
The most common questions about engine codes, what they mean, how to find them and how this database works
The OM646.990 is a robust V8 diesel when properly maintained. Early models (2010-2010) are prone to HPFP failure, but post-2011 revisions significantly improved reliability. Regular oil changes with MB 229.51 oil and use of clean diesel fuel are essential. Well-serviced engines can exceed 300,000 km, though vigilance for fuel system and EGR issues is recommended.
The most documented issues are high-pressure fuel pump failure (especially pre-2011), turbo actuator sticking, EGR cooler leaks, and external oil leaks from valve cover gaskets. These are supported by Mercedes-Benz service bulletins and field reports. Fuel contamination and poor maintenance accelerate these failures.
The OM646.990 was used in the W221 S-Class (S400 CDI BlueTEC, 2010-2013) and V251 Viano (Viano 4.0 CDI BlueTEC, 2010-2013). It was not used in SUVs or coupes. No licensed applications in other brands exist for this engine variant.
Yes, but with caution. ECU remaps can increase output to ~250 kW (340 PS), but place additional stress on the factory HPFP and turbo. Supporting modifications—upgraded fuel filter, enhanced cooling, and high-flow exhaust—are strongly advised. Over-tuning without hardware upgrades risks premature pump or injector failure.
In combined driving, the OM646.990 achieves approximately 9.5–11.0 L/100km (26–30 mpg UK). Highway efficiency improves to ~8.0 L/100km (35 mpg UK), while city driving may reach 13.0 L/100km (22 mpg UK). Real-world consumption depends on vehicle weight and driving style, but it is competitive for a V8 diesel luxury sedan or MPV.
Yes. The OM646.990 is an interference engine. If the timing chain fails or jumps, piston-to-valve contact will occur, resulting in severe internal engine damage. However, the dual front-mounted chain system is robust and rarely fails when maintenance is up to date.
The engine requires MB 229.51 specification oil, typically SAE 5W-30. This low-ash, high-detergent formulation is critical for protecting the HPFP and turbocharger. Oil must be changed every 15,000 km or 12 months. Use of non-compliant oils increases wear and voids component 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
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