The Mercedes — Benz M115.954 is a 2,996 cc, inline — six naturally aspirated petrol engine produced between 1976 and 1980. It features a single overhead camshaft (SOHC) design with two valves per cylinder and a carbureted fuel system. This engine delivers 125 kW (170 PS) at 5,500 rpm and 255 Nm of torque at 3,750 rpm, providing smooth and linear power delivery characteristic of Mercedes — Benz inline — six engines of this era.
Fitted to models such as the W114/W115 280, W116 S — Cl…
Production years 1976–1978 meet German TA-Luft 1974 standards; 1979–1980 models comply with Euro 1 .
The Mercedes-Benz M115.954 is a 2,996 cc inline-six naturally aspirated petrol engine designed for executive sedans and coupes (1976–1980). It combines SOHC architecture with carburetion to deliver smooth, linear power delivery. Engineered to meet early emissions regulations, it balances drivability with acceptable emissions for its period.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,996 cc | |
Fuel type | Petrol (Unleaded, 95 RON min) | |
Configuration | Inline-6, SOHC, 12-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 87.0 mm × 88.0 mm | |
Power output | 125 kW (170 PS) @ 5,500 rpm | |
Torque | 255 Nm @ 3,750 rpm | |
Fuel system | Single-barrel carburetor (Bosch 28/32 PDSI) | |
Emissions standard | Pre-Euro (1976–1978); Euro 1 (1979–1980) | |
Compression ratio | 9.0:1 | |
Cooling system | Water-cooled | |
Turbocharger | N/A | |
Timing system | Single-row timing chain (front-mounted) | |
Oil type | SAE 20W-50 (API SF) | |
Dry weight | 198 kg |
The Mercedes-Benz M115.954 was used across Mercedes-Benz's W114/W115/W116 platforms with longitudinal mounting. This engine received platform-specific adaptations-reinforced mounts in the W116 and tuned exhaust manifolds in the R107-and from 1979 the facelifted W115 models adopted revised camshaft profiles, creating interchange limits. All adaptations are documented in OEM technical bulletins.
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Field reports and technical service bulletins highlight component wear patterns under high-load operation. Adherence to manufacturer service intervals and approved fluid specifications is critical for long-term reliability.
Analysis derived from manufacturer technical service bulletins and industry workshop records. Repair procedures should follow manufacturer guidelines.
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The M115.954 delivers smooth inline-six performance and is generally robust when properly maintained. Early models (1976–1977) are prone to camshaft lobe wear, but post-1978 revisions significantly improved durability. Regular oil changes with SAE 20W-50 API SF oil and timely replacement of known wear items (carburetor, gaskets) ensure long-term reliability.
Key issues include camshaft lobe wear (especially pre-1978), carburetor hesitation or flooding, thermal reactor blockage, and valve cover oil leaks. These are well-documented in Mercedes-Benz technical bulletins. Exhaust manifold cracking and distributor wear are also reported but less critical.
The M115.954 was used in the W114/W115 280 series (1976–1980), W116 S-Class (280S, 280SE, 1976–1979), and R107 SL-Class (280SL, 1977–1980). It replaced the M115.953 and was succeeded by the M115.955. All applications are longitudinal front-engine layouts with 4-speed manual or automatic transmissions.
Limited tuning potential exists. Carburetor upgrades (e.g., dual carbs) or conversion to fuel injection can yield +20–30 kW gains. However, the SOHC design and 9.0:1 compression limit major power increases without internal modifications. Performance camshafts and exhaust headers offer moderate improvements. Always maintain factory cooling and oiling systems when modifying.
Expect 15–18 L/100 km (16–19 mpg UK) in city driving and 10–12 L/100 km (24–28 mpg UK) on highways. Combined consumption typically ranges 12–14 L/100 km (20–24 mpg UK). Real-world figures depend heavily on driving style, given the carbureted engine's sensitivity to throttle use. Using premium fuel (98 RON) can improve smoothness and responsiveness.
Yes. The M115.954 is an interference engine. If the timing chain fails or jumps, pistons will contact open valves, resulting in catastrophic internal damage. This underscores the importance of timely maintenance and immediate attention to any timing-related noises or faults.
Mercedes-Benz specifies SAE 20W-50 oil meeting API SF standard. Use only high-quality mineral or semi-synthetic oil designed for high-load petrol engines and change it every 12,000 km or annually. Proper oil selection is critical for camshaft lubrication and long-term reliability.
Comprehensive technical documentation and regulatory references
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DVLA: Engine Changes & MoT
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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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