The Mercedes-Benz M103.980 is a 2,960 cc, inline-six petrol engine produced between 1986 and 1993. It featured a dual overhead camshaft (DOHC) design with four valves per cylinder and Bosch LE-Jetronic fuel injection. Delivering 138 kW (188 PS) and 270 Nm of torque, it offered refined performance and smoothness for executive sedans and coupes of the era.
Fitted to models such as the W124 300E, W126 300SE, and W201 300CE, the M103.980 was engineered for high-speed stability and effortless cruising. Emissions compliance was achieved via a three-way catalytic converter and closed-loop lambda control, meeting Euro 1 standards for post-1988 models, while earlier units complied with pre-regulatory European norms.
One documented service concern is premature wear of the timing chain tensioner, which can lead to chain slack and camshaft misalignment. This issue, referenced in Mercedes-Benz Service Information Bulletin 07-89-02, is attributed to oil flow restrictions in early tensioner designs. Later production revisions included an updated tensioner assembly and revised oil gallery routing to improve reliability.
Production years 1986–1988 meet pre-Euro standards; 1989–1993 models comply with Euro 1 (VCA UK Type Approval #VCA/EMS/5679).
The Mercedes-Benz M103.980 is a 2,960 cc inline-six petrol engine designed for executive saloons and coupes (1986–1993). It combines DOHC architecture with Bosch LE-Jetronic fuel injection to deliver smooth power delivery and high-speed refinement. Engineered to meet evolving emissions requirements, it balances performance with increasing regulatory demands of the late 1980s.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,960 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, DOHC, 24-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 87.0 mm × 83.6 mm | |
| Power output | 138 kW (188 PS) | |
| Torque | 270 Nm @ 4,000 rpm | |
| Fuel system | Bosch LE-Jetronic (electronic multi-point injection) | |
| Emissions standard | Pre-Euro (1986–1988); Euro 1 (1989–1993) | |
| Compression ratio | 9.7:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | None | |
| Timing system | Double-row timing chain (interference design) | |
| Oil type | SAE 10W-40, API SH | |
| Dry weight | 182 kg |
The naturally aspirated DOHC design provides smooth high-RPM power ideal for highway driving but requires strict adherence to 15,000 km oil change intervals to prevent timing chain tensioner failure and camshaft wear. SAE 10W-40 oil meeting API SH specifications is essential due to its high-temperature stability and anti-wear additives. Extended idling or short-trip driving increases carbon buildup on intake valves. The LE-Jetronic system demands clean fuel and regular filter changes to maintain injector performance. Post-1989 models feature revised tensioner design; pre-1989 units benefit from inspection per Mercedes-Benz SIB 07-89-02. Lambda sensor and catalytic converter health must be monitored to maintain emissions compliance and prevent drivability issues.
Oil Specs: Requires SAE 10W-40, API SH specification (Mercedes-Benz SIB 07-89-02). Compatible with ACEA A2-96.
Emissions: Euro 1 certification applies to 1989–1993 models only (VCA Type Approval #VCA/EMS/5679). Pre-1989 models meet national type approvals under EU Directive 70/220/EEC.
Power Ratings: Measured under DIN 70020 standards. Output consistent across model applications (Mercedes-Benz TIS Doc. A35112).
Mercedes-Benz Technical Information System (TIS): Docs A34730, A35112, SIB 07-89-02
VCA Type Approval Database (VCA/EMS/5679)
ISO 1585:1992 Road vehicles — Engine test code — Net power
The Mercedes-Benz M103.980 was used across Mercedes-Benz's W124/W126 platforms with longitudinal mounting and no licensing partnerships. This engine received platform-specific adaptations-revised intake manifolds in the W124 and modified exhaust manifolds in the W126-and from 1989 the updated W124 models adopted Euro 1-compliant variants with enhanced lambda control, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the front-facing side of the cylinder block, near the exhaust manifold (Mercedes-Benz TIS A34815). The 8th VIN digit indicates engine type ('M' for M103 series). Pre-1989 models feature KE-Jetronic fuel injection with analog control; post-1989 units use LE-Jetronic with digital ECU. Critical differentiation from M103.990: M103.980 has a 2,960 cc displacement and 188 PS output. Service parts require model-year verification—tensioners and ECUs for pre-1989 models are not interchangeable with Euro 1 variants due to emissions revisions (Mercedes-Benz SIB 07-89-02).
The M103.980's primary reliability risk is timing chain tensioner failure on pre-1989 builds, with elevated incidence in high-mileage urban use. Internal Mercedes quality reports from 1991 indicated a notable share of engines requiring tensioner replacement before 180,000 km, while VCA field data links a significant portion of emissions-related failures to lambda sensor degradation in city-driven vehicles. Extended oil intervals and use of non-specified oils increase tensioner and camshaft stress, making oil quality and service adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (1986-1993) and UK VCA failure statistics (1990-2000). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M103980.
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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