The Mercedes — Benz M 110.985 is a 2,778 cc, inline — six naturally aspirated petrol engine produced between 1978 and 1985. It features a single overhead camshaft (SOHC), 12 — valve configuration, and Bosch K — Jetronic mechanical fuel injection. This engine delivers 130 kW (177 PS) at 6,000 rpm and 245 Nm of torque at 4,000 rpm, providing smooth high — RPM performance for grand touring applications.
Fitted primarily to the W123 and W126 series sedans and coupes—including the…
Production years 1978–1981 meet pre-catalyst emissions standards; 1982–1985 models with catalytic converter comply with early Euro-level requirements .
The Mercedes-Benz M 110.985 is a 2,778 cc inline-six naturally aspirated engine engineered for executive sedans and coupes (1978–1985). It combines SOHC valvetrain architecture with Bosch K-Jetronic continuous fuel injection to deliver smooth high-RPM power delivery. Designed for durability and refinement, it meets early catalytic emissions standards in later variants while maintaining strong mechanical reliability.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,778 cc | |
Fuel type | Petrol | |
Configuration | Inline-6, SOHC, 12-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 87.0 mm × 78.0 mm | |
Power output | 130 kW (177 PS) @ 6,000 rpm | |
Torque | 245 Nm @ 4,000 rpm | |
Fuel system | Bosch K-Jetronic mechanical fuel injection | |
Emissions standard | Pre-cat (1978–1981); catalyst-equipped (1982–1985) | |
Compression ratio | 9.0:1 | |
Cooling system | Water-cooled | |
Turbocharger | Not applicable | |
Timing system | Chain-driven camshaft | |
Oil type | Refer to vehicle handbook / manufacturer specification | |
Dry weight | 185 kg |
The Mercedes-Benz M 110.985 was used across Mercedes-Benz's W123 and W126 platforms with longitudinal mounting. This engine received platform-specific adaptations-increased sound insulation in the W126 and modified exhaust manifolds in the W123-and from 1982 the introduction of the catalytic converter for certain markets, 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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Yes, the M 110.985 is a robust and durable engine when properly maintained. Its simple SOHC design and mechanical fuel injection contribute to long service life. However, pre-1982 models without catalysts are more susceptible to fuel system issues if stored or driven infrequently. Regular oil changes, use of correct fuel, and periodic fuel system servicing are essential for sustained reliability beyond 200,000 km.
The most common issues are K-Jetronic fuel distributor degradation, hydraulic lifter noise, ignition timing drift, and coolant leaks from intake manifold gaskets. Fuel system problems are more frequent in low-mileage or stored vehicles. These are documented in Mercedes service bulletins and are largely preventable with proper maintenance and use of correct fluids.
The M 110.985 was used in the W123 series (280E, 280CE) from 1978–1985 and the W126 series (280SE, 280SEL) from 1979–1985. It was offered in both sedan and coupe body styles. All applications feature longitudinal engine mounting and rear-wheel drive. Later models (1982–1985) were equipped with catalytic converters for emissions compliance in key markets.
Limited tuning potential exists due to its mechanical fuel injection and SOHC design. Output can be optimized through precise K-Jetronic calibration, performance camshafts, and exhaust upgrades. Some enthusiasts install later M110 variants with higher compression or retrofit electronic fuel injection. However, significant power gains require extensive modifications and are not common due to the engine's classic status.
Fuel consumption is moderate for its era. In a W123 280E, typical figures are ~13.5 L/100km (city) and ~9.0 L/100km (highway), or approximately 21 mpg UK combined. Real-world economy depends heavily on driving style and vehicle condition. Carburetted contemporaries are less efficient; the K-Jetronic system provides relatively precise fuel metering for a mechanical setup.
No, the M 110.985 is not an interference engine. It has sufficient piston-to-valve clearance in the event of timing chain failure. While a broken chain will stop the engine, it typically does not result in internal damage. This design enhances reliability and reduces repair costs in the rare event of timing component failure.
Mercedes specifies SAE 10W-40 mineral or semi-synthetic oil meeting API SF/CC standards. Change intervals should not exceed 15,000 km or annually. Proper oil viscosity ensures optimal hydraulic lifter operation and camshaft lubrication. Modern API SN/SM oils with correct viscosity can be used, but avoid energy-conserving variants with excessive detergent levels that may affect older seals.
Comprehensive technical documentation and regulatory references
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Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
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