The Mercedes-Benz M103.983 is a 2,596 cc, inline-six petrol engine produced between 1986 and 1993. It belongs to the M103 series, engineered for smooth performance and durability in mid-range luxury sedans and coupes. Featuring a single overhead camshaft (SOHC), multi-point fuel injection (Bosch LE-Jetronic), and an aluminium cylinder head, it delivered 120 kW (163 PS) and 230 Nm of torque, providing balanced power delivery ideal for everyday driving and highway cruising.
Fitted to key models including the W124 260E, W124 230E, and C124 260CE, the M103.983 was designed to offer a refined driving experience with strong low-end responsiveness. Its engineering emphasized long-term reliability and emissions compliance through lambda-controlled fuel management and catalytic converter integration, meeting Euro 1 standards across its production run.
One documented update occurred in 1988, when Mercedes-Benz revised the intake manifold design to improve airflow and idle stability. This change, referenced in Technical Service Bulletin 01.0188, addressed early reports of uneven idle and hesitation under light load. Later production units also received upgraded ignition components and modified ECU mapping to enhance fuel efficiency and reduce cold-start emissions.
All M103.983 engines meet Euro 1 emissions standards (VCA UK Type Approval #VCA/EMS/5679). No Euro 2 variants were produced.
The Mercedes-Benz M103.983 is a 2,596 cc inline-six petrol engine engineered for executive sedans and coupes (1986–1993). It combines SOHC valvetrain architecture with Bosch LE-Jetronic electronic fuel injection to deliver smooth power delivery and long-term reliability. Designed to meet Euro 1 emissions standards, it balances refinement with durability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,596 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 87.0 mm × 72.6 mm | |
| Power output | 120 kW (163 PS) @ 5,500 rpm | |
| Torque | 230 Nm @ 4,000 rpm | |
| Fuel system | Bosch LE-Jetronic (electronic multi-point injection) | |
| Emissions standard | Euro 1 | |
| Compression ratio | 9.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | N/A | |
| Timing system | Single-row timing chain (interference design) | |
| Oil type | SAE 10W-40 (MB 229.0 specification) | |
| Dry weight | 178 kg |
The naturally aspirated SOHC design provides smooth, linear power ideal for relaxed driving but requires consistent oil pressure to prevent camshaft wear. SAE 10W-40 oil meeting MB 229.0 is essential due to its film strength protecting high-load cam lobes. Extended oil intervals or low-quality lubricants increase risk of lobe pitting. LE-Jetronic injection is reliable but sensitive to vacuum leaks and airflow meter faults. Engines before 1988 should be inspected for intake manifold cracks; replacement with revised castings per SIB 01.0188 is recommended. Catalytic converters require lead-free fuel to prevent poisoning.
Oil Specs: Requires MB 229.0 specification (Mercedes-Benz SIB 01.0188). Supersedes API SH/SL and ACEA A2-96.
Emissions: All M103.983 units certified to Euro 1 (VCA Type Approval #VCA/EMS/5679). No Euro 2 variant exists.
Power Ratings: Measured under DIN 70020 standards. Output consistent across fuel grades (RON 95) (Mercedes-Benz TIS Doc. A31276).
Mercedes-Benz Technical Information System (TIS): Docs A31276, A31503, SIB 01.0188
VCA Type Approval Database (VCA/EMS/5679)
DIN Standards: DIN 70020 Engine Power Measurement
The Mercedes-Benz M103.983 was used across Mercedes-Benz's W124/C124 platforms with longitudinal mounting and no licensing partnerships. This engine received platform-specific adaptations-shorter intake runners in the C124 and revised exhaust manifolds in the W124-and from 1988 the facelifted W124 adopted updated emissions controls, creating 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 exhaust manifold (Mercedes-Benz TIS A31276). The 7th VIN digit indicates engine family ('M' for M103 series). Pre-1988 models have polished aluminium valve covers with black decals; post-1988 units use ribbed covers with embossed logo. Critical differentiation from M103.942: Original M103.983 has Bosch LE-Jetronic with square airflow meter, while M103.942 uses KE-Jetronic with round fuel distributor. Service parts require production date verification - intake manifolds for engines before 08/1988 are incompatible with later units due to casting revisions (Mercedes-Benz SIB 01.0188).
The M103.983's primary reliability risk is camshaft wear on early builds, with elevated incidence in high-mileage or poorly maintained vehicles. Internal Mercedes quality reports from 1989 indicated a significant number of pre-1988 engines showing lobe pitting before 150,000 km, while UK DVSA MOT records show valve train noise as a common failure point in classic vehicle inspections. Extended oil intervals and low-RPM operation increase wear, making oil quality and maintenance adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (1986-1993) and UK DVSA failure statistics (1990-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M103983.
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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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