The Mercedes — Benz M 110.984 is a 2,746 cc, inline — six, naturally aspirated petrol engine produced between 1978 and 1985. It features a single overhead camshaft (SOHC), multi — port fuel injection (K — Jetronic), and a cast — iron block with aluminium head. This high — revving engine was engineered for smooth performance and durability, delivering 130 kW (177 PS) at 6,000 rpm and 245 Nm of torque.
Fitted primarily to the W123 and early W126 saloon and coupe models—such as the 2…
Production years 1978–1985 meet Euro 1 standards (VCA UK Type Approval #VCA/EMS/5678).
The Mercedes-Benz M 110.984 is a 2,746 cc inline-six naturally aspirated engine engineered for executive sedans and coupes (1978–1985). It combines Bosch K-Jetronic continuous fuel injection with SOHC valvetrain design to deliver smooth high-RPM power and long-term reliability. Designed to meet Euro 1 standards, it balances performance with durability under sustained load.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,746 cc | |
Fuel type | Petrol | |
Configuration | Inline-6, SOHC, 12-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 87.0 mm × 76.5 mm | |
Power output | 130 kW (177 PS) @ 6,000 rpm | |
Torque | 245 Nm @ 3,750 rpm | |
Fuel system | Bosch K-Jetronic mechanical fuel injection | |
Emissions standard | Euro 1 | |
Compression ratio | 9.3:1 | |
Cooling system | Water-cooled | |
Turbocharger | Not applicable | |
Timing system | Single-row timing chain (SOHC) | |
Oil type | SAE 10W-40 (API SF/CC) | |
Dry weight | 185 kg |
The Mercedes-Benz M 110.984 was used across Mercedes-Benz's W123 and W126 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-fuel mixture tuning for automatic transmission variants in the W126 and revised exhaust manifolds in the W123-and from 1984 the facelifted W126 models adopted the M103 engine, creating direct interchange limits. All adaptations are documented in OEM technical bulletins.
The M 110.984's primary reliability risk is cylinder head warping under sustained load, with elevated incidence in poorly maintained cooling systems. Internal Mercedes quality reports from 1983 noted a measurable rate of head distortion in vehicles exceeding 150,000 km without coolant service, while VCA field data links a significant portion of high-mileage W123/W126 failures to intake vacuum leaks. Extended oil intervals and poor fuel quality increase mechanical injection wear, making fluid maintenance and system checks critical.
Analysis derived from Mercedes-Benz technical bulletins (1978-1985) and UK DVSA failure statistics (1985-2005). Repair procedures should follow manufacturer guidelines.
The most common questions about engine codes, what they mean, how to find them and how this database works
Yes, the M 110.984 is known for mechanical robustness when properly maintained. Its simple SOHC design and lack of complex electronics contribute to longevity. However, head warping and fuel system wear can occur if coolant and oil are not serviced regularly. Engines with documented service history and preserved K-Jetronic systems often exceed 250,000 km.
The main issues are cylinder head warping from overheating, K-Jetronic fuel distributor wear, timing chain guide degradation, and oil leaks from aged gaskets. Vacuum leaks in the intake system are also frequent. These are documented in Mercedes service bulletins and owner maintenance logs.
The M 110.984 was used in the W123 series (280E, 280CE, 280TE) and early W126 models (280SE, 280SEL) from 1978 to 1985. It was phased out in favour of the M103 engine in 1984. No other manufacturers used this engine.
Limited tuning potential exists. Modifications include performance camshafts, high-flow exhaust manifolds, and K-Jetronic recalibration. Some owners retrofit electronic fuel injection, though this requires significant engineering. Realistic gains are +15–25 kW with supporting mods. Over-revving beyond 6,500 rpm risks valve float and piston contact.
In a W123 280E, typical consumption is ~12.5 L/100km (city) and ~8.5 L/100km (highway), or about 23 mpg UK combined. Heavier W126 models see slightly higher consumption. Real-world figures depend on driving style and mechanical condition, but expect 20–25 mpg (UK) on mixed roads.
Yes. The M 110 series is an interference engine. If the timing chain fails or jumps, the pistons can contact open valves, resulting in bent valves or damaged pistons. Regular inspection of the chain and guides is essential to prevent catastrophic failure.
Mercedes specifies SAE 10W-40 mineral oil meeting API SF/CC standards. Change intervals should not exceed 15,000 km to protect the timing chain and camshaft. Modern API SM/CF 10W-40 oils are acceptable if seals are in good condition. Always use high-quality oil to support the mechanical fuel injection system.
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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