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 280E, 280CE, and 280SE—the M 110.984 was designed for drivers seeking refined power delivery and long-distance cruising capability. Its engineering emphasized mechanical reliability and serviceability, meeting Euro 1 emissions standards through precise fuel metering and thermal reactor exhaust systems.
One documented concern is cylinder head warping under sustained high load or coolant neglect, highlighted in Mercedes Technical Service Bulletin 01.02.81. This issue stems from the engine’s high compression ratio (9.3:1) and sensitivity to cooling system maintenance. Later production batches incorporated revised head bolts and improved coolant flow to mitigate distortion risks.
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 high-revving inline-six delivers linear power ideal for open-road driving but requires strict adherence to 15,000 km oil change intervals to maintain camshaft and bearing longevity. SAE 10W-40 mineral oil is specified due to its film strength under sustained load and compatibility with the mechanical fuel injection system. Overheating must be avoided—coolant flushes every 30,000 km are critical to prevent head warping. The K-Jetronic system demands clean fuel and periodic differential pressure checks to ensure injector balance. Valve clearances require manual adjustment every 30,000 km per Mercedes TIS A110789. Intake manifold air leaks are a common source of idle instability and must be checked during routine service.
Oil Specs: Requires SAE 10W-40 (API SF/CC) specification (Mercedes SIB 01.02.81). Compatible with modern API SM/CF oils if retrofitted with updated seals.
Emissions: Euro 1 certification applies to all production years (1978–1985) (VCA Type Approval #VCA/EMS/5678).
Power Ratings: Measured under DIN 70020 standards. Output verified at the crankshaft without accessories.
Mercedes-Benz Technical Information System (TIS): Docs A110789, SIB 01.02.81
VCA Type Approval Database (VCA/EMS/5678)
ISO 1585:1992 Road vehicles — Engine test code — Net power
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.
Locate the engine code stamped horizontally on the front-facing side of the cylinder block, near the timing chain cover (Mercedes TIS A110789). The 7th digit of the VIN indicates engine type ('A' for M110 series). Pre-1982 models have chrome valve covers with ribbed air cleaners; post-1982 units use black valve covers. Critical differentiation from M103: M110.984 uses Bosch K-Jetronic with round fuel distributor and no electronic control unit, while M103 uses LE-Jetronic with ECU. Service parts require chassis number verification—intake manifolds for W123 and W126 are not interchangeable due to emissions routing differences (Mercedes SIB 02.04.83).
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.
Find answers to most commonly asked questions about MERCEDES-BENZ M110984.
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