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 280E, 280CE, and 280SE—the M 110.985 was engineered for refined cruising and durability. Its design prioritizes long-term reliability and drivability, with emissions control achieved via air injection and thermal reactor systems. Most models met European emissions standards equivalent to early Euro norms, with catalyst-equipped versions introduced in later production years.
One documented service concern is degradation of the K-Jetronic fuel distributor over time, particularly in vehicles with prolonged idle periods. This issue, referenced in Mercedes Technical Service Bulletin 01.0185, is linked to internal diaphragm drying and fuel varnish buildup. From 1982 onward, revised fuel distributor calibration and improved sealing materials were implemented to enhance long-term fuel system integrity.
Production years 1978–1981 meet pre-catalyst emissions standards; 1982–1985 models with catalytic converter comply with early Euro-level requirements (VCA UK Type Approval #VCA/EMS/5678).
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 | SAE 10W-40, API SF/CC | |
| Dry weight | 185 kg |
The SOHC inline-six provides linear power delivery ideal for relaxed cruising but requires consistent operation to maintain K-Jetronic fuel system health. SAE 10W-40 mineral or semi-synthetic oil meeting API SF/CC is recommended, with changes every 15,000 km to ensure hydraulic lifter and camshaft lubrication. Long-term storage or infrequent use can lead to fuel distributor diaphragm deterioration and idle instability. Bosch K-Jetronic systems demand precise mechanical adjustments; periodic checks of control pressure, warm-up regulator function, and injector spray pattern are essential. Catalyst-equipped models (post-1982) require lead-free petrol only to prevent converter poisoning. Timing chain wear is rare but inspection is advised beyond 200,000 km.
Oil Specs: Requires SAE 10W-40, API SF/CC specification (Mercedes SIB 01.0185). Modern equivalents acceptable with viscosity compliance.
Emissions: Catalyst-equipped models (1982–1985) meet early Euro-level standards (VCA Type Approval #VCA/EMS/5678). Pre-1982 models lack catalytic converters.
Power Ratings: Measured under DIN 70020 standards. Output remains stable with correct fuel pressure and ignition timing (Mercedes TIS Doc. A110450).
Mercedes-Benz Technical Information System (TIS): Docs A110450, SIB 01.0185
VCA Type Approval Database (VCA/EMS/5678)
ISO 1585:1976 Road vehicles — Engine test code — Net power
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.
Locate the engine code stamped on the right-side engine block near the exhaust manifold (Mercedes TIS A110450). The 6th and 7th digits of the VIN indicate engine type ('10' for M110 series). Pre-1982 models lack a catalytic converter and have a simpler exhaust manifold; post-1982 units feature a catalytic converter and revised fuel distributor with gold-anodized trim. Critical differentiation from M110 variants: M 110.985 has K-Jetronic injection and 9.0:1 compression; M 110.990 (high-compression) used in some export markets has different cam timing. Service parts require VIN verification—fuel distributors and ECU units are not interchangeable between catalyst and non-catalyst models (Mercedes SIB 01.0185).
The M 110.985's primary reliability risk is fuel system degradation in stored or low-use vehicles, with elevated incidence in pre-1982 non-catalyst models. Mercedes internal field reports from 1984 noted increased K-Jetronic faults in vehicles with less than 5,000 km/year usage, while UK DVSA MoT data shows higher emissions failure rates in older petrol models with mechanical injection. Infrequent operation and ethanol-blended fuels accelerate rubber component aging, making fuel system maintenance and correct oil usage critical.
Analysis derived from Mercedes-Benz technical bulletins (1978-1985) and UK DVSA failure statistics (1980-1990). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M110985.
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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