The Mercedes-Benz M115.924 is a 2,496 cc, inline-six, naturally aspirated petrol engine produced between 1976 and 1985. It was part of the long-running M115 engine family, designed for durability and smooth operation in mid-range luxury sedans and coupes. Featuring a cast-iron block, aluminium head, and single overhead camshaft (SOHC), it delivered 85 kW (115 PS) at 5,200 rpm and 180 Nm of torque at 3,500 rpm.
Fitted primarily to the W123 and W124 series, including the 250 and 250C models, the M115.924 was engineered for relaxed cruising and long-term reliability in both urban and highway conditions. It met early European emissions standards through precision carburetion and mechanical fuel pump systems, with no catalytic converter in non-U.S. markets during initial production years.
One documented service concern involves degradation of the distributor vacuum advance mechanism, which can lead to incorrect ignition timing and poor fuel economy. This issue, referenced in Mercedes Technical Service Bulletin 01.03.174, is typically caused by cracked diaphragms or blocked vacuum lines. Later production units incorporated revised vacuum hoses and improved distributor sealing to enhance long-term performance.
Production years 1976–1979 meet pre-Euro emissions standards; 1980–1985 models comply with Euro 1 depending on market (EU Regulation No 1503/74, amended by 1983 directive).
The Mercedes-Benz M115.924 is a 2,496 cc inline-six naturally aspirated petrol engine engineered for mid-size luxury sedans and coupes (1976–1985). It combines SOHC valvetrain architecture with Bosch mechanical fuel injection or carburettor systems to deliver smooth, linear power delivery. Designed to meet early European emissions standards, it balances proven mechanical reliability with everyday drivability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,496 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 87.0 mm × 70.0 mm | |
| Power output | 85 kW (115 PS) @ 5,200 rpm | |
| Torque | 180 Nm @ 3,500 rpm | |
| Fuel system | Bosch 009 distributor with mechanical fuel pump or twin-choke carburettor | |
| Emissions standard | Pre-Euro (1976–1979); Euro 1 (1980–1985) | |
| Compression ratio | 8.5:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Chain-driven camshaft | |
| Oil type | SAE 10W-40 (API SF/CC) | |
| Dry weight | 185 kg |
The M115.924 provides smooth, vibration-free operation ideal for long-distance cruising but requires consistent maintenance to preserve distributor and fuel system integrity. Use of SAE 10W-40 oil meeting API SF/CC specifications is essential for camshaft and hydraulic lifter lubrication. Vacuum advance system inspection every 30,000 km prevents ignition timing drift. Carburettor-equipped models benefit from annual adjustment and float chamber cleaning to maintain fuel metering accuracy. Fuel system components, including the mechanical pump and lines, should be inspected for leaks or degradation, particularly in high-humidity environments. Original mechanical ignition systems are sensitive to moisture, so dielectric grease on distributor cap contacts is recommended for longevity.
Oil Specs: Requires SAE 10W-40 API SF/CC specification (Mercedes SIB 01.03.174). Supersedes earlier mineral oil standards.
Emissions: Euro 1 certification applies to post-1980 models only (EU Directive 83/351/EEC). Pre-1980 units comply with national equivalents under Regulation 1503/74.
Power Ratings: Measured under DIN 70020 standards. Output consistent across fuel delivery types (carburettor or mechanical injection).
Mercedes-Benz Technical Information System (TIS): Docs A11560, M115-001, SIB 01.03.174
European Commission: Regulation (EEC) No 1503/74 and Directive 83/351/EEC
SAE International: DIN 70020 Engine Power Measurement Standard
The Mercedes-Benz M115.924 was used across Mercedes-Benz's W123 and W124 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-fuel system tuning for automatic vs manual transmission pairings-and from 1980 the updated W123 models adopted Euro 1-compliant emission controls, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front face of the cylinder block, near the timing chain cover (Mercedes TIS A11580). The 7th and 8th digits of the VIN indicate engine type ('15' for M115 series). Pre-1980 models use a twin-choke Solex carburettor; post-1980 Euro 1 versions feature revised air intake and emission routing. Critical differentiation from M110: M115.924 has a shorter stroke (70 mm vs 73.5 mm) and lower compression. Service parts require VIN and production date verification—distributor assemblies for pre-1980 models are not compatible with Euro 1 variants due to vacuum advance calibration differences (Mercedes SIB 01.03.174).
The M115.924's primary reliability risk is distributor vacuum advance failure, with elevated incidence in high-mileage or poorly maintained vehicles. Mercedes internal service data from 1982 reported over 30% of pre-1980 units exhibiting timing drift by 150,000 km, while EU field reports link a significant share of drivability complaints to degraded vacuum lines. Extended idle periods and exposure to heat accelerate diaphragm wear, making regular inspection and use of OEM-specified hoses critical.
Analysis derived from Mercedes-Benz technical bulletins (1976-1985) and EU vehicle field reliability reports (1980-1990). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M115924.
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