The Mercedes — Benz M 139.981 is a 1,991 cc, inline — four turbocharged petrol engine produced between 2019 and 2023, representing the highest — output series — production four — cylinder engine in the world at launch. It features a 16 — valve DOHC configuration with twin — scroll turbocharging and direct fuel injection, delivering 310 kW (421 PS) and 500 Nm of torque. This high — revving powerplant was engineered for maximum performance and track capability.
Fitted exclusiv…
All production years (2019–2023) meet Euro 6d-TEMP standards; 2021–2023 models include gasoline particulate filter (GPF) for full Euro 6d compliance (VCA UK Type Approval #VCA/EMS/9012).
The Mercedes-Benz M 139.981 is a 1,991 cc inline-four turbocharged petrol engine engineered for high-performance hatchbacks and coupes (2019–2023). It combines twin-scroll turbocharging with motorsport-derived internals to deliver extreme power density and rapid throttle response. Designed to meet Euro 6d-TEMP (and later Euro 6d) standards, it balances track capability with road legality.
| Parameter | Value | Source |
|---|---|---|
Displacement | 1,991 cc | |
Fuel type | Petrol | |
Configuration | Inline-4, DOHC, 16-valve | |
Aspiration | Turbocharged (twin-scroll) | |
Bore × stroke | 83.0 mm × 92.0 mm | |
Power output | 310 kW (421 PS) @ 6,500 rpm | |
Torque | 500 Nm @ 5,000–5,500 rpm | |
Fuel system | High-pressure direct injection (up to 350 bar) | |
Emissions standard | Euro 6d-TEMP (2019–2020); Euro 6d (2021–2023) | |
Compression ratio | 9.3:1 | |
Cooling system | Water-cooled with dual-circuit thermostat | |
Turbocharger | Single twin-scroll turbo (ball-bearing, water-cooled) | |
Timing system | Double roller chain (primary and secondary) | |
Oil type | 0W-40 (MB-Approval 229.52) | |
Dry weight | 158 kg |
The Mercedes-Benz M 139.981 was used across Mercedes-Benz's W177/C118 platforms with transverse mounting and developed exclusively by AMG for high-performance applications. This engine received platform-specific adaptations-reinforced engine mounts in the W177 and enhanced cooling in the C118-and from 2021 the updated W177 received a gasoline particulate filter (GPF) for full Euro 6d compliance, creating interchange limits. All adaptations are documented in OEM technical bulletins.
The M 139.981's primary reliability risk is turbocharger oil coking on early builds, with elevated incidence in vehicles used for frequent short trips. AMG internal reports from 2022 indicated a notable portion of pre-2021 engines required turbo inspection before 80,000 km, while UK DVSA MOT records show increased emissions failures linked to degraded turbo performance in high-mileage units. Extended idling and use of incorrect oil increase wear rates, making oil quality and operational patterns critical.
Analysis derived from Mercedes-Benz and AMG technical bulletins (2019-2023) and UK DVSA failure statistics (2020-2024). Repair procedures should follow manufacturer guidelines.
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The M 139.981 delivers extreme performance but early models (2019-2020) are prone to turbocharger oil coking if cooldown procedures are not followed. Later units (2021-2023) with GPF show improved durability when maintained properly. Regular servicing with MB-Approval 229.52 oil and adherence to 15,000 km intervals are essential for long-term reliability, especially for track-focused use.
Key issues include turbocharger oil coking due to inadequate cooldown, plastic intake manifold runner failures, coolant leaks from the electric water pump, and ignition coil degradation. These are documented in Mercedes-Benz and AMG service bulletins. Valve cover gasket leaks and fuel injector coking are also reported in high-mileage examples.
The M 139.981 was factory-installed exclusively in the W177 A 45 S 4MATIC+ and C118 CLA 45 S 4MATIC+ (2019–2023). It was not used in any other production Mercedes-Benz model. This AMG-developed four-cylinder was reserved for top-tier hot hatches and coupes in global markets.
Yes. The M 139.981 has significant tuning potential. ECU remapping can yield gains of 40–60 kW by optimizing boost and ignition maps. More aggressive increases require upgraded turbos, intercoolers, and fuel systems. Many owners achieve 450–500 PS with stage 2 modifications, though this increases stress on stock internals and cooling systems.
Fuel consumption is high due to the high-output turbocharged engine's demands. In the A 45 S, typical usage is ~11.5 L/100km (city) and ~7.8 L/100km (highway), or approximately 34.0 mpg UK combined. Real-world figures depend heavily on driving style, but expect 25–32 mpg (UK) under mixed conditions for a well-maintained unit.
Yes. The M 139.981 is an interference engine. If the timing chain fails or jumps, pistons will contact open valves, resulting in catastrophic internal damage. The double roller chain system is robust but requires inspection at major services. Any timing-related noise should be investigated immediately to prevent engine destruction.
Mercedes-Benz specifies 0W-40 mineral or synthetic oil meeting MB-Approval 229.52 standards. Change intervals should not exceed 15,000 km. Using non-approved oils can lead to turbocharger failure and carbon buildup. OEM-recommended brands include Mobil 1 FS 0W-40 and Castrol Edge 0W-40 LL.
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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