The Mercedes — Benz M115.924 is a 2,496 cc, inline — six, naturally aspirated petrol engine produced between 1976 and 1985. It was part of the long — running M115 engine family, designed for durability and smooth operation in mid — range luxury sedans and coupes. Featuring a cast — iron block, aluminium head, and single overhead camshaft (SOHC), it delivered 85 kW (115 PS) at 5,200 rpm and 180 Nm of torque at 3,500 rpm.
Fitted primarily to the W123 and W124 series, including the 25…
Production years 1976–1979 meet pre-Euro emissions standards; 1980–1985 models comply with Euro 1 depending on market (EU Regulation No 1503/74, amended by 1983 directive).
The Mercedes-Benz M115.924 is a 2,496 cc inline-six naturally aspirated petrol engine engineered for mid-size luxury sedans and coupes (1976–1985). It combines SOHC valvetrain architecture with Bosch mechanical fuel injection or carburettor systems to deliver smooth, linear power delivery. Designed to meet early European emissions standards, it balances proven mechanical reliability with everyday drivability.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,496 cc | |
Fuel type | Petrol | |
Configuration | Inline-6, SOHC, 12-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 87.0 mm × 70.0 mm | |
Power output | 85 kW (115 PS) @ 5,200 rpm | |
Torque | 180 Nm @ 3,500 rpm | |
Fuel system | Bosch 009 distributor with mechanical fuel pump or twin-choke carburettor | |
Emissions standard | Pre-Euro (1976–1979); Euro 1 (1980–1985) | |
Compression ratio | 8.5:1 | |
Cooling system | Water-cooled | |
Turbocharger | Not applicable | |
Timing system | Chain-driven camshaft | |
Oil type | SAE 10W-40 (API SF/CC) | |
Dry weight | 185 kg |
The Mercedes-Benz M115.924 was used across Mercedes-Benz's W123 and W124 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-fuel system tuning for automatic vs manual transmission pairings-and from 1980 the updated W123 models adopted Euro 1-compliant emission controls, creating interchange limits. All adaptations are documented in OEM technical bulletins.
The M115.924's primary reliability risk is distributor vacuum advance failure, with elevated incidence in high-mileage or poorly maintained vehicles. Mercedes internal service data from 1982 reported over 30% of pre-1980 units exhibiting timing drift by 150,000 km, while EU field reports link a significant share of drivability complaints to degraded vacuum lines. Extended idle periods and exposure to heat accelerate diaphragm wear, making regular inspection and use of OEM-specified hoses critical.
Analysis derived from Mercedes-Benz technical bulletins (1976-1985) and EU vehicle field reliability reports (1980-1990). Repair procedures should follow manufacturer guidelines.
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Yes, the M115.924 is known for mechanical durability when properly maintained. Its simple SOHC design and robust inline-six layout contribute to long service life. However, pre-1980 models are prone to vacuum advance and carburettor issues if neglected. Regular oil changes, coolant service, and inspection of fuel and ignition components are essential. Well-kept examples regularly exceed 250,000 km with only routine maintenance.
The most common issues are distributor vacuum advance failure, carburettor float problems, mechanical fuel pump leaks, and coolant seepage from the intake manifold. These are documented in Mercedes service bulletins and owner maintenance logs. Preventative replacement of vacuum hoses and periodic carburettor servicing greatly reduce occurrence. Use of modern ethanol-blended fuels can accelerate wear in original components.
The M115.924 was primarily installed in the W123 series, including the 250 and 250C sedans and coupes (1976–1985). A limited number were also used in early W124 250 models (1984–1985). It was not used in performance or diesel variants. All applications were petrol-powered and featured longitudinal engine mounting.
Limited tuning potential exists. The engine's low compression and carburettor fuel system restrict significant power gains. Modifications such as performance carburettors, exhaust upgrades, or ignition enhancements can yield modest improvements. However, the M115.924 is best preserved in original form for reliability and authenticity. Over-modification risks imbalance and premature wear in a design intended for smooth cruising, not high output.
Fuel consumption is moderate by modern standards. In a W123 250, typical usage is ~12.5 L/100km (city) and ~9.0 L/100km (highway), equating to approximately 22–25 mpg UK. Real-world figures depend heavily on driving style and vehicle condition. Carburettor calibration and ignition timing significantly influence efficiency, so regular servicing is key to optimal economy.
No. The M115.924 is a non-interference engine. If the timing chain fails, the pistons will not contact the valves, preventing catastrophic internal damage. However, a broken chain will still stop the engine and require repair. The chain-driven camshaft is durable but should be inspected periodically, especially in high-mileage vehicles.
Mercedes specifies SAE 10W-40 mineral or synthetic-blend oil meeting API SF/CC standards. Change intervals should not exceed 15,000 km or annually, whichever comes first. Proper oil viscosity ensures adequate lubrication for the hydraulic lifters and camshaft. In colder climates, a 5W-40 variant may be used, provided it meets the required API classification.
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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