The Mercedes — Benz OM668.942 is a 3,996 cc, V8 turbo — diesel engine produced between 2006 and 2011. It was engineered as a high — performance diesel powerplant for luxury and performance applications, featuring common — rail direct injection, variable geometry turbocharging (VGT), and DOHC valvetrain architecture. In standard tune it delivered 210 kW (286 PS) and 700 Nm of torque, providing strong low — end response suitable for high — speed and towing applications.
Fit…
All production years 2006–2011 meet Euro 4 emissions standards .
The Mercedes-Benz OM668.942 is a 3,996 cc V8 turbo-diesel engineered for full-size luxury vehicles (2006–2011). It combines common-rail direct injection with a single variable-geometry turbocharger to deliver strong low-end torque and smooth power delivery. Designed to meet Euro 4 standards, it balances premium refinement with robust diesel efficiency.
| 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 | 210 kW (286 PS) @ 3,600 rpm | |
Torque | 700 Nm @ 1,600–2,400 rpm | |
Fuel system | Bosch CRS 2.0 common-rail (up to 1,600 bar) | |
Emissions standard | Euro 4 | |
Compression ratio | 17.0:1 | |
Cooling system | Water-cooled | |
Turbocharger | Single variable-geometry turbo (Garrett GT2260V) | |
Timing system | Dual-row roller chain (front-mounted) | |
Oil type | Refer to vehicle handbook / manufacturer specification | |
Dry weight | 238 kg |
The Mercedes-Benz OM668.942 was used across Mercedes-Benz's W221/R230 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-longer intake manifolds in the W221 and revised exhaust routing in the R230-and from 2009 the facelifted W221 LCI models adopted updated EGR cooling, creating interchange limits. All adaptations are documented in OEM technical bulletins.
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Field reports and technical service bulletins highlight component wear patterns under high-load operation. Adherence to manufacturer service intervals and approved fluid specifications is critical for long-term reliability.
Analysis derived from manufacturer technical service bulletins and industry workshop records. Repair procedures should follow manufacturer guidelines.
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The OM668.942 offers strong torque and smooth operation, but pre-2008 models are prone to high-pressure fuel pump wear if maintenance is delayed. Later units with updated pumps and filters show improved durability. Regular oil changes using MB 229.51 5W-30 and high-quality diesel fuel are essential for longevity. Well-maintained examples can exceed 250,000 km without major repairs.
Key issues include high-pressure fuel pump degradation, EGR valve/coolant clogging, turbo actuator sticking, and valve cover oil leaks. These are documented in Mercedes-Benz service bulletins, particularly SIB 20/2008 for the HPFP. Carbon buildup in intake and EGR systems is common in city-driven vehicles with short trip cycles.
This 4.0L V8 diesel was used in the W221 S-Class (S 420 CDI) and R230 SL-Class (SL 420 CDI) from 2006 to 2011. It was not offered in other model lines or licensed to third parties. All units meet Euro 4 emissions standards and feature longitudinal engine mounting.
Aftermarket ECU tuning is common on the OM668942 platform, but increasing boost or altering engine parameters accelerates component wear, impacts emissions compliance, and may void vehicle warranties. Any modifications should be evaluated carefully by a qualified specialist.
In the S 420 CDI (W221), typical consumption is ~12.4 L/100km (city), ~7.8 L/100km (highway), or ~9.6 L/100km combined (29 mpg UK). Real-world figures vary by driving style, but expect 28–32 mpg (UK) in mixed conditions. The V8 layout and vehicle weight result in lower efficiency compared to smaller diesels.
Yes. The OM668 series is an interference engine. If the timing chain fails or skips, pistons will contact open valves, resulting in severe internal damage. The front-mounted dual-row chain is robust but requires proper lubrication. Any abnormal noise from the timing cover should prompt immediate inspection.
Mercedes-Benz specifies SAE 5W-30 oil meeting MB 229.51 standard. This low-ash formulation protects the EGR and turbo systems and ensures proper HPFP lubrication. Oil changes should occur every 15,000 km or annually, whichever comes first, to maintain engine longevity and prevent deposit formation.
Comprehensive technical documentation and regulatory references
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Regulatory Stability
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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
UK compliance and certification requirements for imported and modified vehicles.
VCA Certification Portal
Type-approval guidance and documentation.
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