The Mercedes — Benz OM 646.982 is a 3,996 cc, V8 twin — turbo diesel engine produced between 2011 and 2018. 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 250 kW (340 PS) at 3,600 rpm and 760 Nm of torque between 2,000–2,600 rpm.
Fitted to models such as the W222 S400 CDI, W21…
Production years 2011–2015 meet Euro 5 standards; 2016–2018 models comply with Euro 6 (VCA UK Type Approval #VCA/EMS/9821).
The Mercedes-Benz OM 646.982 is a 3,996 cc V8 twin-turbo diesel engineered for executive and SUV platforms (2011–2018). It combines common-rail direct injection with sequential twin-turbocharging to deliver strong mid-range torque and refined performance. Designed to meet Euro 5 and Euro 6 standards, it balances power delivery with advanced 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 | 250 kW (340 PS) @ 3,600 rpm | |
Torque | 760 Nm @ 2,000–2,600 rpm | |
Fuel system | Bosch CRS 3-18 common-rail (up to 1,800 bar) | |
Emissions standard | Euro 5 (pre-2016); Euro 6 (2016–2018) | |
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 | 240 kg |
The Mercedes-Benz OM 646.982 was used across Mercedes-Benz's W222/W217/W166 platforms with longitudinal mounting and no external licensing. This engine received platform-specific adaptations-reinforced mounts in the W166 SUV and revised cooling routing in the W222 limousine-and from 2014 the W217 received updated fuel filtration, creating interchange limits. All adaptations are documented in OEM technical bulletins.
The OM 646.982'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 2016 noted increased HPFP failures in W222 S400 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 (2011-2018) and UK DVSA failure statistics (2015-2023). Repair procedures should follow manufacturer guidelines.
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Yes, the OM 646.982 is generally reliable when properly maintained. Its robust V8 twin-turbo design allows many examples to exceed 300,000 km. Key risks include high-pressure fuel pump wear and DPF/SCR clogging. Regular oil changes, use of MB 229.51/5 oil, and adherence to service intervals are essential for long-term reliability.
The most common issues are high-pressure fuel pump failure due to poor fuel quality, EGR and intake carbon buildup, DPF clogging from short trips, and SCR/AdBlue system faults. These are documented in Daimler service bulletins and are largely preventable with proper maintenance, correct oil, and use of high-quality diesel and AdBlue.
The OM 646.982 was used in the W222 S400 CDI (2013–2017), W217 CLS400 CDI (2011–2018), W166 GL400 CDI (2012–2015), and W166 GLE400 CDI (2015–2018). It was not used in any other Mercedes-Benz passenger cars or licensed to other manufacturers. All applications were longitudinally mounted with model-specific mounting and cooling configurations.
Yes, the OM 646.982 responds well to ECU remapping. Stage 1 tunes typically yield 380–400 PS with minimal risk, as the engine and fuel system can handle increased torque. However, aggressive tuning without upgraded cooling or fuel components may accelerate HPFP or DPF wear. Always use reputable tuners and maintain service quality.
In real-world driving, the OM 646.982 achieves approximately 12.0–14.0 L/100km (24–20 mpg UK), depending on vehicle weight and driving style. The W222 S400 CDI typically returns ~12.8 L/100km (22 mpg UK) on mixed routes. Its large-displacement V8 design and twin-turbo efficiency balance performance with acceptable diesel economy for its class.
Yes. The OM 646.982 is an interference engine. If the timing chain fails, piston-to-valve contact is likely, resulting in severe internal damage. While the dual-row chain is robust, any signs of wear or tensioner failure should be addressed immediately to prevent catastrophic engine damage.
The OM 646.982 requires MB 229.51 (SAE 5W-30) or MB 229.5 (SAE 5W-40) engine oil. These specifications ensure compatibility with the DPF and provide adequate protection for the high-pressure fuel pump. Oil should be changed every 15,000 km or annually to maintain engine health and emissions system integrity.
Comprehensive technical documentation and regulatory references
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EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
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UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
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Vehicle Certification Agency (VCA)
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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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