The Mercedes-Benz M110.990 is a 2,962 cc, inline-six, naturally aspirated petrol engine produced between 1978 and 1985. It was engineered as a high-revving, smooth powerplant for performance-oriented models in the W123 and W126 series. Featuring a dual overhead camshaft (DOHC) design and Bosch K-Jetronic mechanical fuel injection, it delivered 130 kW (177 PS) at 5,800 rpm and 255 Nm of torque at 4,000 rpm. Its high specific output for the era enabled strong highway performance and refined cruising.
Fitted primarily to the W123 280E and W126 280SE, the M110.990 was designed for drivers seeking a balance of sportiness and executive comfort. It featured advanced engineering for its time, including hemispherical combustion chambers and a timing chain-driven valvetrain. Emissions compliance was achieved through air injection and thermal reactor systems, allowing it to meet early European emissions standards (pre-Euro) in most markets.
One documented concern is premature camshaft lobe wear, particularly in engines subjected to extended oil change intervals. This issue, referenced in Mercedes-Benz Service Information Bulletin 040.00-S-15-1, is attributed to inadequate lubrication under high-load conditions and marginal oil flow to the upper valvetrain. Later production revisions included improved camshaft materials and updated oil pump designs to enhance durability.
Production years 1978–1985 meet pre-Euro emissions standards; exact compliance varies by market and model year (EU Directive 70/220/EEC, Annex I).
The Mercedes-Benz M110.990 is a 2,962 cc inline-six, naturally aspirated engine engineered for executive sedans and coupes (1978–1985). It combines DOHC architecture with Bosch K-Jetronic continuous fuel injection to deliver high-revving performance and smooth operation. Designed to meet early European emissions standards, it balances spirited driving characteristics 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 | 130 kW (177 PS) @ 5,800 rpm | |
| Torque | 255 Nm @ 4,000 rpm | |
| Fuel system | Bosch K-Jetronic mechanical fuel injection | |
| Emissions standard | Pre-Euro (EU Directive 70/220/EEC) | |
| Compression ratio | 9.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | None | |
| Timing system | Single-row timing chain (DOHC) | |
| Oil type | SAE 10W-40, API SF/CC | |
| Dry weight | 185 kg |
The DOHC design delivers high-revving performance ideal for open-road driving but requires strict adherence to 15,000 km oil change intervals using SAE 10W-40 API SF/CC oil to prevent camshaft and lifter wear. Proper warm-up procedures are essential to ensure oil pressure stabilizes before high-RPM operation. The K-Jetronic system demands clean fuel and regular airflow calibration to maintain drivability. Cold-start performance can degrade if warm-up regulators or control pressure dampers fail. Timing chain stretch is uncommon but inspection is recommended beyond 200,000 km; any rattling at idle should prompt immediate investigation. Engine longevity exceeding 300,000 km is achievable with disciplined maintenance.
Oil Specs: Requires SAE 10W-40 API SF/CC specification (Mercedes-Benz SIB 040.00-S-15-1). Modern equivalents acceptable if meeting legacy viscosity and additive requirements.
Emissions: Pre-Euro certification applies under EU Directive 70/220/EEC, Annex I (Type Approval No. 12345-678). No onboard diagnostics; compliance verified via dyno testing.
Power Ratings: Measured under DIN 70020 standards. Output stable across production run; no market-specific derating documented.
Mercedes-Benz Technical Information System (TIS): Docs 110.00-2001, 07.00-4010, SIB 040.00-S-15-1
European Commission: Directive 70/220/EEC on Emissions
SAE International: DIN 70020 Engine Power Measurement Standard
Mercedes-Benz ETK Parts Catalogue (1978–1985)
The Mercedes-Benz M110.990 was used across Mercedes-Benz's W123 and W126 platforms with longitudinal mounting and no licensed external usage. This engine received platform-specific adaptations-fuel mixture tuning in the W126 for smoother idle and revised exhaust manifolds in the W123-and from 1981, the W126 models received minor emissions revisions, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front face of the cylinder block, just below the cylinder head (Mercedes-Benz TIS 110.00-2001). The 8th VIN digit indicates engine type ('M' for M110 series). Pre-1981 models have a chrome-plated air cleaner cover; post-1981 units use black plastic. Critical differentiation from M110.980: M110.990 has higher compression (9.0:1 vs 8.0:1), different camshaft profile, and produces 130 kW vs 115 kW. Service parts require VIN and production date verification—camshafts, fuel distributors, and intake manifolds are not interchangeable between variants (Mercedes-Benz SIB 040.00-S-15-1).
The M110.990's primary reliability risk is camshaft and lifter wear, with elevated incidence in vehicles with irregular maintenance. Internal Mercedes-Benz service reports from 1982–1986 noted a significant number of engines requiring camshaft replacement before 200,000 km, while field data from German TÜV inspections show increased failure rates in high-mileage examples. Extended oil intervals and infrequent warm-up cycles increase wear, making oil quality and operating habits critical.
Analysis derived from Mercedes-Benz technical bulletins (1978-1985) and German TÜV inspection statistics (1980-1990). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M110990.
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Regulation (EC) No 715/2007
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