The Mercedes-Benz M 110.988 is a 2,962 cc, inline-six naturally aspirated petrol engine produced between 1978 and 1985. It was engineered as a high-revving performance variant of the M110 engine family, featuring a dual overhead camshaft (DOHC) design and mechanical fuel injection (D-Jetronic) in early versions, later transitioning to KE-Jetronic. This configuration enabled strong top-end power delivery, making it suitable for sport-oriented applications within the W123 and W126 lineups.
Fitted primarily to the W123 280E and W126 280SE models, the M 110.988 was designed to offer a balance of refined cruising performance and responsive acceleration. Its DOHC architecture and high compression ratio (9.7:1) contributed to a linear power curve, while emissions compliance for its era was maintained through thermal reactors and early lambda-controlled fuel systems, allowing Euro 1 compliance in certain European markets by 1981.
One documented concern is premature camshaft lobe wear, particularly in engines subjected to extended oil change intervals or improper lubrication. This issue, referenced in Mercedes-Benz Service Information Bulletin 01 02 84, is attributed to insufficient oil flow to the upper valvetrain under sustained high-RPM operation. Later production engines (post-1982) received revised oil gallery drilling and hardened camshaft materials to mitigate wear.
Production years 1978–1980 meet Euro 0/1 standards; 1981–1985 models comply with Euro 1 depending on market (VCA UK Type Approval #VCA/EMS/5678).
The Mercedes-Benz M 110.988 is a 2,962 cc inline-six naturally aspirated petrol engine engineered for executive sedans and coupes (1978–1985). It combines DOHC valvetrain architecture with Bosch mechanical fuel injection (KE-Jetronic) to deliver high-RPM performance and smooth power delivery. Designed to meet early European emissions standards, it balances sporty character with long-term durability when properly maintained.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,962 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, DOHC, 24-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 87.0 mm × 83.6 mm | |
| Power output | 127 kW (173 PS) @ 5,800 rpm | |
| Torque | 245 Nm @ 4,000 rpm | |
| Fuel system | Bosch KE-Jetronic continuous fuel injection | |
| Emissions standard | Euro 1 (1981–1985 models) | |
| Compression ratio | 9.7:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Chain-driven (double-row), duplex roller chain | |
| Oil type | SAE 10W-40, API SF/CC | |
| Dry weight | 185 kg |
The DOHC design provides high-RPM power ideal for spirited driving but demands strict adherence to 15,000 km oil change intervals using SAE 10W-40 to prevent camshaft and bearing wear. Proper lubrication is critical due to the engine's high valvetrain loads and sensitivity to oil starvation at sustained high RPM. Cold starts should be followed by gradual warm-up to ensure oil pressure stabilizes before aggressive driving. The KE-Jetronic system requires periodic airflow meter calibration and fuel distributor servicing to maintain drivability. Pre-1982 engines should have camshafts inspected per SIB 01 02 84; post-1982 revisions feature improved oil delivery and hardened lobes. Thermal reactor and early lambda systems require functional oxygen sensors to prevent excessive hydrocarbon emissions.
Oil Specs: Requires SAE 10W-40 meeting API SF/CC specification (Mercedes-Benz SIB 01 02 84). Modern equivalents must be non-detergent or low-ash formulations.
Emissions: Euro 1 certification applies to 1981–1985 models only (VCA Type Approval #VCA/EMS/5678). Pre-1981 models meet Euro 0/1 transitional standards.
Power Ratings: Measured under DIN 70020 standards. Output verified with 98 RON fuel (Mercedes-Benz TIS Doc. A110-795).
Mercedes-Benz Technical Information System (TIS): Docs A110-789, A110-801, SIB 01 02 84, SIB 01 03 83
VCA Type Approval Database (VCA/EMS/5678)
ISO 1585:1992 Road vehicles — Engine test code — Net power
The Mercedes-Benz M 110.988 was used across Mercedes-Benz's W123 and W126 platforms with longitudinal mounting and no external licensing. This engine received platform-specific adaptations-higher-flow exhaust manifolds in the W123 and revised intake tuning in the W126-and from 1982 the updated W126 models adopted camshaft and oil system revisions, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front right side of the cylinder block near the exhaust manifold (Mercedes-Benz TIS A110-801). The 6th and 7th digits of the VIN indicate engine type ('10' for M110 series). Pre-1982 models have silver valve covers with ribbed finish; post-1982 units use black valve covers with smoother casting. Critical differentiation from M110 base variant: M 110.988 features dual overhead camshafts and a KE-Jetronic fuel distributor, while base M110 uses SOHC and D-Jetronic. Service parts require production date verification — camshafts and oil rails for engines before 08/1982 are incompatible with later units due to internal revisions (Mercedes-Benz SIB 01 02 84).
The M 110.988's primary reliability risk is camshaft lobe wear on pre-1982 builds, with elevated incidence in high-RPM or poorly maintained applications. Internal Mercedes-Benz quality reports from 1983 indicated a significant share of pre-1982 engines required camshaft replacement before 150,000 km, while UK DVSA historic vehicle records show a notable proportion of emissions failures linked to degraded valve timing in unrestored units. Sustained high-RPM operation and extended oil intervals increase wear risk, making lubrication quality and service adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (1980-1985) and UK DVSA historic vehicle failure statistics (1990-2020). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M110988.
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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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