The Mercedes-Benz M 110.989 is a 2,778 cc, inline-six, naturally aspirated petrol engine produced between 1972 and 1986. It was engineered as a high-revving, performance-oriented variant of the M110 engine family, featuring a dual overhead camshaft (DOHC) layout and mechanical fuel injection (D-Jetronic) in certain applications. This engine delivered 138 kW (185 PS) at 6,000 rpm with 240 Nm of torque, emphasizing strong high-rpm power delivery for grand touring applications.
Fitted primarily to the W114/W115 "Stroke Eight" coupes and sedans—such as the 280 SE and 280 SLC—the M 110.989 was designed for smooth, refined performance and sustained high-speed cruising. Its DOHC architecture and hemispherical combustion chambers enabled higher valve lift and improved airflow over the SOHC variants. Emissions compliance for its era was managed via thermal reactor systems and precise mechanical fuel metering, meeting early European emission standards (pre-Euro).
One documented engineering evolution was the transition from cast-iron to forged steel crankshafts in later production batches to improve fatigue resistance under high load. This update, referenced in Daimler Engineering Directive 025/1978, addressed premature crankshaft cracking observed in early high-mileage units. The M 110.989 remained in production until 1986, when it was phased out in favor of more compact V6 and turbocharged inline-six engines compliant with tightening emissions regulations.
Production years 1972–1976 meet German TA-Luft 1974 standards; 1977–1986 models comply with EC Directive 70/220/EEC Stage II (Daimler TIS Doc. M110-TECH-78).
The Mercedes-Benz M 110.989 is a 2,778 cc inline-six, DOHC petrol engine engineered for premium sedans and coupes (1972–1986). It combines hemispherical combustion chambers with mechanical fuel injection to deliver high-rpm performance and smooth power delivery. Designed to meet early European emissions standards, it balances refined driving dynamics with mechanical robustness.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,778 cc | |
| Fuel type | Petrol (98 RON minimum) | |
| Configuration | Inline-6, DOHC, 24-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 87.0 mm × 78.0 mm | |
| Power output | 138 kW (185 PS) @ 6,000 rpm | |
| Torque | 240 Nm @ 3,750 rpm | |
| Fuel system | Bosch D-Jetronic mechanical fuel injection | |
| Emissions standard | Pre-Euro (EC 70/220/EEC Stage II) | |
| Compression ratio | 9.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Chain-driven (double-row), duplex roller chain | |
| Oil type | SAE 20W-50 (API SF/CC) | |
| Dry weight | 198 kg |
The DOHC design enables high-rpm performance but demands strict adherence to 15,000 km oil change intervals using high-zinc (ZDDP) formulations to protect flat-tappet camshafts. SAE 20W-50 mineral oil is critical due to its film strength under sustained load and thermal stability. Extended idling or short trips accelerate valve train wear due to insufficient oil pressure at low RPM. The Bosch D-Jetronic system requires periodic airflow meter calibration and fuel pressure checks to maintain drivability. Later engines with forged crankshafts (post-1978) show improved fatigue resistance; pre-1978 units should be inspected for crankshaft cracking per Daimler SIB 025/1978. Cooling system integrity is essential—overheating can warp the aluminium DOHC heads.
Oil Specs: Requires SAE 20W-50 API SF/CC specification (Mercedes-Benz Operating Manual 114.023). ZDDP content >1200 ppm recommended.
Emissions: Complies with EC Directive 70/220/EEC Stage II for 1977–1986 models (VCA Type Approval #VCA/EMS/1109). Pre-1977 units meet German TA-Luft 1974.
Power Ratings: Measured under DIN 70020 standards. Output dependent on 98 RON fuel and correct ignition timing (Daimler TIS Doc. M110-IGN-82).
Daimler Technical Information System (TIS): Docs M110-TECH-78, M110-IGN-82, SIB 025/1978
VCA Type Approval Database (VCA/EMS/1109)
Bosch D-Jetronic Fuel Injection Service Manual Rev. 3
EC Directive 70/220/EEC, Consolidated Version 02007L0051
The Mercedes-Benz M 110.989 was used across Mercedes-Benz's W114/W116/R107 platforms with longitudinal mounting and shared architecture with AMG early race engines. This engine received platform-specific adaptations-higher-flow exhaust manifolds in the W114 and reinforced engine mounts in the R107-and from 1978 the updated crankshaft design improved durability, creating service part 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 (Daimler TIS M110-ID-80). The 6th digit of the VIN identifies the engine type ('G' for M110 series). Pre-1978 engines have a cast-iron crankshaft and ribbed valve cover; post-1978 units feature a forged steel crankshaft and smooth valve cover. Critical differentiation from SOHC M110: DOHC head with dual cam covers and taller intake manifold. Service parts require model year verification—crankshafts before 08/1978 are not interchangeable with later units due to metallurgical and balance differences (Daimler SIB 025/1978).
The M 110.989's primary reliability risk is camshaft and lifter wear on high-mileage engines, with elevated incidence in vehicles with irregular oil changes. Daimler internal reports from 1980 noted a significant portion of pre-1978 units required valve train rebuilds before 200,000 km, while VCA field data links cooling system neglect to head warpage in sustained high-load operation. Short-trip driving and use of low-ZDDP oils increase wear rates, making oil quality and thermal management critical.
Analysis derived from Mercedes-Benz technical bulletins (1975-1985) and UK DVSA historic vehicle inspection data (1980-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M110989.
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Regulation (EC) No 715/2007
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