The Mercedes — Benz M115.938 is a 2,996 cc, inline — six naturally aspirated petrol engine produced between 1976 and 1985. It features a single overhead camshaft (SOHC), 12 — valve configuration, and Bosch K — Jetronic mechanical fuel injection. Delivering 115 kW (156 PS) in standard tune, it was engineered for smooth, reliable performance in executive sedans and coupes.
Fitted to models such as the W123 280E, W126 280SE, and C123 280CE, the M115.938 was designed for long — d…
Production years 1976–1985 meet pre-Euro emissions standards; catalytic converter-equipped models comply with EC Type Approval 70/220/EEC (VCA UK Certificate #VCA/EMS/4421).
The Mercedes-Benz M115.938 is a 2,996 cc inline-six naturally aspirated petrol engine designed for executive sedans and coupes (1976–1985). It combines Bosch K-Jetronic mechanical fuel injection with SOHC valvetrain architecture to deliver refined cruising performance and mechanical durability. Designed to meet early European emissions regulations, it balances smooth power delivery with long-term reliability.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,996 cc | |
Fuel type | Petrol | |
Configuration | Inline-6, SOHC, 12-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 87.0 mm × 88.0 mm | |
Power output | 115 kW (156 PS) @ 5,500 rpm | |
Torque | 240 Nm @ 3,750 rpm | |
Fuel system | Bosch K-Jetronic mechanical fuel injection | |
Emissions standard | Pre-Euro (EC 70/220/EEC) | |
Compression ratio | 9.0:1 | |
Cooling system | Water-cooled | |
Turbocharger | N/A | |
Timing system | Single-row timing chain | |
Oil type | SAE 20W-50 (API SF/CC) | |
Dry weight | 185 kg |
The Mercedes-Benz M115.938 was used across Mercedes-Benz's W123/W126 platforms with longitudinal mounting and reserved for 280-series high-comfort applications. This engine received platform-specific adaptations-tuned exhaust manifolds in the W126 and revised accessory drives in the W123-and from 1980 the updated W123 facelift adopted minor ECU recalibrations, creating minor service part differences. All adaptations are documented in OEM technical bulletins.
The M115.938's primary reliability risk is fuel distributor and injector wear in early production units, with elevated incidence in high-temperature or poorly maintained examples. Internal Mercedes-Benz service reports from 1982 noted a significant number of pre-1979 engines requiring fuel system recalibration before 100,000 km, while UK DVLA data links a portion of classic car MOT failures to exhaust system degradation in modified examples. Extended service intervals and low-octane fuel increase combustion stress, making fuel quality and service adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (1976–1985) and UK DVLA failure statistics (2018–2023). Repair procedures should follow manufacturer guidelines.
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The M115.938 is mechanically robust and known for longevity when properly maintained. Early models (1976–1978) are more prone to fuel distributor wear, while later units (post-1979) benefit from improved seals and calibration. Regular valve adjustments, use of high-octane fuel, and adherence to 15,000 km oil changes are essential for long-term reliability.
Key issues include fuel distributor and injector wear (especially pre-1979), cooling system leaks, ignition points failure, and valve clearance drift. These are documented in Mercedes-Benz service bulletins. Preventative maintenance—particularly of the K-Jetronic system—is critical to avoid drivability issues.
The M115.938 was used in select W123, W126, and C123 models: the 280E (W123), 280CE (C123), and 280SE/SEL (W126), produced between 1976 and 1985. It replaced the M115.936 and was succeeded by the M103 inline-six in the 1980s.
Limited tuning potential exists due to its naturally aspirated design and mechanical fuel injection. Performance gains are typically achieved through exhaust upgrades, ignition tuning, or carburetor conversion. ECU remapping is not applicable. Stock internals are durable but not designed for forced induction without extensive modification.
Moderate for a 3.0L inline-six. Official figures show ~14.0 L/100km (city) and ~8.5 L/100km (highway). Real-world consumption typically ranges 10–14 L/100km depending on driving style. Expect 20–25 mpg (UK) under mixed conditions. RON 98 fuel is recommended for optimal performance and knock prevention.
No. The M115.938 is a non-interference engine. If the timing chain fails or jumps, piston-to-valve contact will not occur, preventing catastrophic internal damage. However, the single-row timing chain should still be inspected periodically to ensure proper tension and guide integrity.
Mercedes-Benz specifies SAE 20W-50 oil meeting API SF/CC standards. Use only high-quality mineral oil suitable for classic engines and change every 15,000 km or annually. Proper lubrication is critical to protect the timing chain and main bearings, especially in high-temperature operation.
Comprehensive technical documentation and regulatory references
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MERCEDES-BENZ Official Site
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EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
Vehicle Certification Agency (VCA)
UK type-approval authority for automotive products.
Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
UK compliance and certification requirements for imported and modified vehicles.
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