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), the OM646.990 was engineered for enhanced refinement and emissions compliance. Emissions control was achieved via cooled exhaust gas recirculation (EGR), diesel particulate filter (DPF), and selective catalytic reduction (SCR) with AdBlue injection, meeting Euro 5 standards across all markets during its production run.
One documented reliability concern is high-pressure fuel pump (HPFP) internal wear, particularly in early production units. This issue, referenced in Mercedes-Benz Service Information Bulletin 20/2010, is attributed to insufficient lubricity in early ultra-low-sulfur diesel formulations. From 2011, revised HPFP internals and updated fuel additive specifications were introduced to improve durability.
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 OM646.990 provides strong low-end torque ideal for towing and luxury driving but requires adherence to 15,000 km oil change intervals using MB 229.51 specification oil to protect the HPFP and turbocharger. Use of EN 590 ultra-low-sulfur diesel is mandatory to prevent injector and pump damage. The Bosch CRS 2.0 system is sensitive to fuel contamination; pre-filter maintenance is advised in regions with variable fuel quality. Early HPFP units (pre-2011) should be inspected per SIB 20/2010; updated pumps with hardened components are recommended for longevity. SCR/AdBlue and DPF systems require periodic regeneration and inspection to maintain emissions compliance and prevent limp-mode events.
Oil Specs: Requires MB 229.51 (5W-30) specification (Mercedes-Benz SIB 20/2010). Not compatible with older 229.31 or ACEA A3/B4 oils.
Emissions: Euro 5 certification applies to all models (2010-2013) (VCA Type Approval #VCA/EMS/6781). No Euro 6 version exists.
Power Ratings: Measured under DIN 70020 standards. Output consistent across fuel grades meeting EN 590 (Mercedes-Benz TIS Doc. A36822).
Mercedes-Benz Technical Information System (TIS): Docs A36014, A36217, SIB 20/2010
VCA Type Approval Database (VCA/EMS/6781)
ISO 1585: Road vehicles — Engine test code — Net power
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.
Locate the engine ID plate mounted on the left-side cylinder head near the intake manifold (Mercedes-Benz TIS A36027). The 8th VIN digit indicates engine type ('J' for OM646 series). Pre-2011 models have a Bosch HPFP with black housing and serial prefix 0445 010 003; post-2011 units use a revised pump with silver housing and prefix 0445 010 006. Critical differentiation from OM642: OM646.990 has a 90° V8 configuration with front-mounted timing covers, while OM642 is a V6. Service parts require VIN and production date verification—HPFP kits for pre-2011 engines are not interchangeable with updated designs (Mercedes-Benz SIB 20/2010).
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.
Find answers to most commonly asked questions about MERCEDES-BENZ OM646990.
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EUR-Lex
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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