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, W217 CLS400 CDI, and W166 GL400 CDI, the OM 646.982 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 AdBlue-based selective catalytic reduction (SCR), allowing most units to meet Euro 5 standards, with later builds achieving full Euro 6 compliance.
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-1008-1, is linked to contamination or lubricity issues in ultra-low-sulfur diesel (ULSD). From 2014, revised pump internals and updated fuel filtration were introduced to improve durability.
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 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-2014 models feature improved fuel filtration; pre-2014 units benefit from upgraded inline filters. EGR, DPF, and SCR 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 W222/W217). Ensures DPF regeneration and fuel pump longevity.
Emissions: Euro 5 certification applies to pre-2016 models only (VCA Type Approval #VCA/EMS/9821). Euro 6 compliance applies to 2016–2018 models with AdBlue injection.
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-1008-1
VCA Type Approval Database (VCA/EMS/9821)
ISO 1585:1976 Road vehicles — Engine test code — Net power
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.
Locate the engine code stamped horizontally on the front-facing side of the cylinder block, just below the intake manifold (Daimler TIS 646.982-0100). The 9th digit of the VIN identifies the engine type ('D' for diesel). Pre-2014 units have a single-stage fuel filter housing; post-2014 models use a dual-stage design with water separator. Critical differentiation from OM 646.812: OM 646.982 includes AdBlue SCR system on post-2016 Euro 6 models. Service parts require chassis number verification—cooling manifolds for W222 models differ from W217 due to routing revisions (Daimler SIB 70.00-P-1008-1).
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.
Find answers to most commonly asked questions about MERCEDES-BENZ OM646982.
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