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-distance comfort and durability. It met emissions requirements through air injection and catalytic converter systems, enabling compliance with early European emissions standards (pre-Euro). The engine's robust cast-iron block and conservative tuning contributed to high longevity under regular maintenance.
One documented characteristic is sensitivity to fuel quality and injector wear over extended service periods. This issue, referenced in Mercedes-Benz Service Information Bulletin 07 0501, stems from the continuous-flow K-Jetronic system’s reliance on precise fuel metering. Later production units incorporated improved injector seals and revised fuel distributor calibration to enhance long-term reliability.
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 inline-six layout provides smooth, vibration-free operation ideal for highway cruising but requires consistent use of high-octane fuel (RON 98) to prevent pre-ignition in hot climates. The K-Jetronic system demands meticulous maintenance—fuel distributor calibration, injector flow testing, and warm-up regulator function are critical for idle stability and emissions compliance. Oil changes every 15,000 km using SAE 20W-50 ensure adequate bearing protection in high-temperature operation. Pre-1980 engines should be inspected for fuel distributor wear per Mercedes-Benz SIB 07 0501; later units benefit from revised O-rings and improved metering plunger durability.
Oil Specs: Requires SAE 20W-50 (API SF/CC) specification (Mercedes-Benz SIB 07 0501). Compatible with MIL-L-2104B standards.
Emissions: EC 70/220/EEC certification applies to all models (VCA Certificate #VCA/EMS/4421). No Euro compliance as production predates Euro 1.
Power Ratings: Measured under DIN 70020 standards. Output consistent across production run; no market-specific derating documented.
Mercedes-Benz Technical Information System (TIS): Docs A34051, SIB 07 0501
VCA Type Approval Database (VCA/EMS/4421)
DIN Standards: DIN 70020 Engine Power Measurement
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.
Locate the engine code stamped vertically on the left-side engine block near the cylinder head (Mercedes-Benz TIS A34051). The 6th and 7th VIN digits indicate engine type ('10' for M115 series). Pre-1980 models feature chrome valve covers with Mercedes-Benz lettering; post-1980 units retain similar styling with updated emissions labels. Critical differentiation from M110: M115.938 has a 3.0L inline-six layout and 156 PS output, while M110 is a 2.0L inline-four with 110 PS. Service parts require model-year verification—fuel distributors for pre-1979 engines are incompatible with later revisions due to calibration updates (Mercedes-Benz SIB 07 0501).
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.
Find answers to most commonly asked questions about MERCEDES-BENZ M115938.
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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