The Mercedes-Benz M156.981 is a 6,208 cc, naturally aspirated V8 petrol engine produced between 2006 and 2011. It was developed as a high-performance powerplant for AMG models, featuring a 90° V8 configuration, dual overhead camshafts (DOHC), and four valves per cylinder. In standard form it delivered 386 kW (525 PS), with peak torque of 630 Nm, providing strong high-RPM power delivery and track-capable performance.
Fitted to performance models such as the W221 S-Class (S 63 AMG), W203 C-Class (C 63 AMG), and R230 SL-Class (SL 63 AMG), the M156.981 was engineered for dynamic driving and high-speed stability. It featured Bosch MED 17.7 engine management with direct fuel injection (CGI), enabling precise air-fuel control and improved thermal efficiency. Emissions compliance was achieved through dual catalytic converters, allowing the engine to meet Euro 4 standards across its production run.
One documented concern is premature wear of the timing chain tensioners, which can lead to noise and potential timing misalignment. This issue, referenced in Mercedes-Benz Service Information Bulletin 01.01.170, is linked to oil starvation under sustained high-RPM operation. In 2009, an updated tensioner design and revised oil gallery routing were introduced to improve lubrication and reduce failure incidence.
All production years 2006–2011 meet Euro 4 emissions standards (VCA UK Type Approval #VCA/EMS/7890).
The Mercedes-Benz M156.981 is a 6,208 cc V8 naturally aspirated engine engineered for high-performance AMG applications (2006–2011). It combines DOHC architecture with CGI direct injection to deliver high-RPM power and responsive throttle characteristics. Designed to meet Euro 4 standards, it balances track-ready performance with drivability in luxury performance vehicles.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 6,208 cc | |
| Fuel type | Petrol | |
| Configuration | 90° V8, DOHC, 32-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 102.2 mm × 94.6 mm | |
| Power output | 386 kW (525 PS) @ 6,800 rpm | |
| Torque | 630 Nm @ 5,200 rpm | |
| Fuel system | Bosch MED 17.7 CGI direct injection (up to 200 bar) | |
| Emissions standard | Euro 4 | |
| Compression ratio | 12.3:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Chain-driven (double-row, duplex chain) | |
| Oil type | 5W-40 MB 229.5 | |
| Dry weight | 208 kg |
The naturally aspirated V8 provides linear, high-RPM power ideal for performance driving but requires strict adherence to 15,000 km oil change intervals using 5W-40 MB 229.5 specification to prevent timing chain wear and bearing degradation. Use of non-compliant oils accelerates wear in high-load conditions. The Bosch MED 17.7 system requires periodic injector cleaning and adaptation resets to maintain throttle response. Pre-2009 engines should have tensioner and guide rail inspected per SIB 01.01.170; later units benefit from improved oil routing. Cooling system integrity is critical due to high thermal loads—inspect radiator, hoses, and thermostat regularly to prevent overheating. CGI injectors are sensitive to fuel quality; only premium unleaded petrol meeting EN 228 should be used.
Oil Specs: Requires MB 229.5 5W-40 (Mercedes-Benz SIB 01.01.170). Supersedes ACEA A3/B4.
Emissions: Euro 4 certification applies to all models (2006–2011) (VCA Type Approval #VCA/EMS/7890).
Power Ratings: Measured under DIN 70020 standards. Output consistent across fuel qualities (Mercedes-Benz TIS Doc. A36020).
Mercedes-Benz Technical Information System (TIS): Docs A36020, A36050, SIB 01.01.170
VCA Type Approval Database (VCA/EMS/7890)
ISO 1585: Road vehicles — Engine test code — Net power
The Mercedes-Benz M156.981 was used across Mercedes-Benz's W221/W203/R230 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-reinforced mounts in the W221 and revised intake manifolds in the R230-and from 2009 the updated tensioner and oil gallery revisions in later builds, creating partial 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, near the timing cover (Mercedes-Benz TIS A36020). The 8th VIN digit indicates engine type ('M' for M156 series). Pre-2009 engines have silver cam covers with "M156" branding; post-2009 units use black cam covers with revised tensioner housings. Critical differentiation from M159: M156.981 is naturally aspirated with CGI injection, while M159 is supercharged. Service parts require model-year verification—tensioners and timing kits for pre-2009 engines are not interchangeable with later revisions due to oil feed and guide updates (Mercedes-Benz SIB 01.01.170).
The M156.981's primary reliability risk is timing chain tensioner wear in pre-2009 units, with elevated incidence in high-mileage vehicles. Internal Mercedes-Benz quality reports from 2010 noted a significant number of early engines requiring tensioner replacement before 120,000 km, while UK DVSA MOT records show elevated engine-related failures in AMG models with deferred maintenance. Extended oil intervals and use of non-compliant oils increase wear rates, making oil quality and schedule adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (2006-2011) and UK DVSA failure statistics (2008-2015). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M156981.
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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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