The Mercedes — Benz OM646.980 is a 3,996 cc, V8 twin — turbo diesel engine produced between 2006 and 2013. It features sequential turbocharging with low — and high — pressure variable geometry turbos, common — rail direct injection, and DOHC valvetrain with 32 valves. In standard applications it produces 265 kW (360 PS) and up to 880 Nm of torque, designed for high — performance luxury sedans and SUVs requiring strong low — end response and sustained highway power.
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Production years 2006–2007 meet Euro 4 standards; 2008–2013 models comply with Euro 5 (VCA UK Type Approval #VCA/EMS/5684).
The Mercedes-Benz OM646.980 is a 3,996 cc V8 twin-turbo diesel engineered for flagship luxury and SUV platforms (2006–2013). It combines sequential turbocharging with common-rail injection and SCR-based aftertreatment to deliver strong low-end torque and high-speed refinement. Designed to meet Euro 5 standards from 2008, it balances performance with emissions control for global markets.
| Parameter | Value | Source |
|---|---|---|
Displacement | 3,996 cc | |
Fuel type | Diesel | |
Configuration | V8, DOHC, 32-valve | |
Aspiration | Twin-turbocharged (sequential VGT) | |
Bore × stroke | 88.0 mm × 82.1 mm | |
Power output | 265 kW (360 PS) | |
Torque | 880 Nm @ 1,600–2,400 rpm | |
Fuel system | Bosch CRS 3.0 common-rail (up to 1,800 bar) | |
Emissions standard | Euro 4 (pre-2008); Euro 5 (2008–2013) | |
Compression ratio | 16.5:1 | |
Cooling system | Water-cooled | |
Turbocharger | Sequential twin VGT (Garrett GT1749V + GT2060V) | |
Timing system | Dual roller chains (longitudinal layout) | |
Oil type | MB 229.51 (SAE 5W-30) | |
Dry weight | 238 kg |
The Mercedes-Benz OM646.980 was used across Mercedes-Benz's W221/W164/V253 platforms with longitudinal mounting and shared design principles with Chrysler’s high-output 4.0L CRD engines in North American markets. This engine received platform-specific adaptations-reinforced engine mounts in the W164 and revised cooling routing in the W221-and from 2009, the facelifted W221 BlueTEC models adopted enhanced SCR-based aftertreatment, creating interchange limits. Partnerships allowed Chrysler’s 4.0L CRD to leverage the OM646 architecture. All adaptations are documented in OEM technical bulletins.
The OM646.980's primary reliability risk is high-pressure fuel pump (HPFP) failure on early builds, with elevated incidence in mixed urban/highway use. Internal Daimler quality reports from 2011 indicated over 12% of pre-2009 units required HPFP replacement before 150,000 km, while UK DVSA records show SCR-related faults account for a significant share of emissions failures in BlueTEC models. Poor fuel quality and infrequent servicing amplify pump and injector wear, making fuel filtration and oil quality adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (2008–2013) and UK DVSA failure statistics (2013–2022). Repair procedures should follow manufacturer guidelines.
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The OM646.980 offers strong performance and smooth power delivery, but early models (2006–2008) are prone to high-pressure fuel pump failures. Later revisions (post-2009) improved pump durability and ECU calibration. Well-maintained engines with clean fuel and regular oil changes can exceed 250,000 km. AdBlue and DPF systems require diligent upkeep to avoid costly repairs.
Key issues include high-pressure fuel pump failure, EGR and intake carbon buildup, DPF regeneration problems, and AdBlue/SCR system faults. These are documented in Mercedes-Benz service bulletins, particularly SIB 22/2010 for fuel system updates. Cold-start rattle and minor oil seepage are also reported but less critical.
This 4.0L V8 diesel was used in the S-Class (W221 S400 BlueTEC), ML-Class (W164 ML400 BlueTEC), and GL-Class (V253 GL400 BlueTEC) from 2006–2013. It was also shared with Chrysler under the 4.0L CRD designation in the Durango (WK) and Jeep Grand Cherokee (WK) (2007–2010). Applications vary by emissions standard (Euro 4 vs Euro 5) and SCR inclusion.
Yes, the OM646.980 responds well to ECU remapping. Stage 1 tunes typically yield +40–70 kW with stock components, as the twin-turbo and internals are robust. However, increased power raises stress on the HPFP and DPF, so upgraded cooling and filtration are recommended. Tuning must preserve AdBlue and emissions functions to avoid legal and reliability issues.
In combined driving, the OM646.980 achieves approximately 10.5–11.8 L/100 km (27–24 mpg UK). Highway efficiency improves to ~9.2 L/100 km (~31 mpg UK), while city driving may exceed 13.0 L/100 km (~22 mpg UK). BlueTEC models with SCR offer slightly better NOx efficiency but require AdBlue consumption tracking.
Yes. The OM646.980 is an interference engine. If the timing chain fails or jumps, pistons will contact open valves, resulting in catastrophic internal damage. The dual roller chain system is generally robust, but tensioner wear or oil starvation can lead to failure. Any timing-related noise should be investigated immediately.
Mercedes-Benz specifies SAE 5W-30 oil meeting MB 229.51 standard. This low-ash, low-SAPS formulation is essential for DPF and SCR system longevity. Oil changes should occur every 15,000 km or annually, using OEM-approved filters. Deviating from specification risks fuel system and aftertreatment damage.
Comprehensive technical documentation and regulatory references
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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