The Mercedes-Benz M103.985 is a 2,960 cc, inline-six petrol engine produced between 1989 and 1996. It features a dual overhead camshaft (DOHC) design with four valves per cylinder and Bosch LE-Jetronic fuel injection. Rated at 143 kW (195 PS) and 270 Nm of torque, it delivers refined performance and smooth power delivery ideal for executive saloons and coupes.
Fitted to models such as the W124 300E, W126 300SE, and W124 300CE, the M103.985 was engineered for balanced driving dynamics, combining responsive throttle response with long-distance comfort. Emissions compliance was achieved through a three-way catalytic converter and closed-loop lambda control, meeting Euro 1 standards for post-1992 models, while earlier units complied with pre-regulatory European norms.
One documented service concern is premature wear of the hydraulic valve lifters, which can lead to increased valve train noise and reduced performance. This issue, referenced in Mercedes-Benz Service Information Bulletin 07-89-03, is attributed to oil flow restrictions in early lifter designs and extended oil change intervals. Later production revisions included updated lifter materials and revised oil gallery routing to improve reliability.
Production years 1989–1992 meet pre-Euro standards; 1993–1996 models comply with Euro 1 (VCA UK Type Approval #VCA/EMS/5680).
The Mercedes-Benz M103.985 is a 2,960 cc inline-six petrol engine designed for executive saloons and coupes (1989–1996). 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 early 1990s.
| 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 | 143 kW (195 PS) | |
| Torque | 270 Nm @ 4,000 rpm | |
| Fuel system | Bosch LE-Jetronic (electronic multi-point injection) | |
| Emissions standard | Pre-Euro (1989–1992); Euro 1 (1993–1996) | |
| Compression ratio | 9.7:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | None | |
| Timing system | Double-row timing chain (non-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 hydraulic lifter wear and camshaft degradation. 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-1993 models feature revised lifter design; pre-1993 units benefit from inspection per Mercedes-Benz SIB 07-89-03. 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 07-89-03). Compatible with ACEA A2-96.
Emissions: Euro 1 certification applies to 1993–1996 models only (VCA Type Approval #VCA/EMS/5680). Pre-1993 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. A35115).
Mercedes-Benz Technical Information System (TIS): Docs A34735, A35115, SIB 07-89-03
VCA Type Approval Database (VCA/EMS/5680)
ISO 1585:1992 Road vehicles — Engine test code — Net power
The Mercedes-Benz M103.985 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 1993 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 A34820). The 8th VIN digit indicates engine type ('M' for M103 series). Pre-1993 models feature KE-Jetronic fuel injection with analog control; post-1993 units use LE-Jetronic with digital ECU. Critical differentiation from M103.980: M103.985 has identical displacement but 195 PS output. Service parts require model-year verification—lifters and ECUs for pre-1993 models are not interchangeable with Euro 1 variants due to emissions revisions (Mercedes-Benz SIB 07-89-03).
The M103.985's primary reliability risk is hydraulic lifter wear on pre-1993 builds, with elevated incidence in high-mileage urban use. Internal Mercedes quality reports from 1994 indicated a notable share of engines requiring lifter 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 lifter and camshaft stress, making oil quality and service adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (1989-1996) and UK VCA failure statistics (1990-2000). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M103985.
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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