The Mercedes-Benz M115.954 is a 2,996 cc, inline-six naturally aspirated petrol engine produced between 1976 and 1980. It features a single overhead camshaft (SOHC) design with two valves per cylinder and a carbureted fuel system. This engine delivers 125 kW (170 PS) at 5,500 rpm and 255 Nm of torque at 3,750 rpm, providing smooth and linear power delivery characteristic of Mercedes-Benz inline-six engines of this era.
Fitted to models such as the W114/W115 280, W116 S-Class (280S, 280SE), and R107 SL-Class (280SL), the M115.954 was engineered for balanced performance and refinement in executive sedans and grand tourers. Emissions control was achieved via a thermal reactor and exhaust gas recirculation (EGR) system, meeting early federal emissions standards in key markets such as Germany and the United States.
One documented service concern is premature camshaft wear, identified in Mercedes-Benz Service Information Bulletin 03/1978 (No. 115.010). This issue stems from inadequate lubrication under high-load conditions and extended oil change intervals. Later production units received revised camshaft materials and improved oil flow calibration to enhance durability.
Production years 1976–1978 meet German TA-Luft 1974 standards; 1979–1980 models comply with Euro 1 (VCA UK Type Approval #VCA/EMS/6789).
The Mercedes-Benz M115.954 is a 2,996 cc inline-six naturally aspirated petrol engine designed for executive sedans and coupes (1976–1980). It combines SOHC architecture with carburetion to deliver smooth, linear power delivery. Engineered to meet early emissions regulations, it balances drivability with acceptable emissions for its period.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,996 cc | |
| Fuel type | Petrol (Unleaded, 95 RON min) | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 87.0 mm × 88.0 mm | |
| Power output | 125 kW (170 PS) @ 5,500 rpm | |
| Torque | 255 Nm @ 3,750 rpm | |
| Fuel system | Single-barrel carburetor (Bosch 28/32 PDSI) | |
| Emissions standard | Pre-Euro (1976–1978); Euro 1 (1979–1980) | |
| Compression ratio | 9.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | N/A | |
| Timing system | Single-row timing chain (front-mounted) | |
| Oil type | SAE 20W-50 (API SF) | |
| Dry weight | 198 kg |
The naturally aspirated inline-six provides smooth, predictable power ideal for relaxed driving but requires adherence to 12,000 km oil change intervals using SAE 20W-50 API SF oil to prevent camshaft wear. Extended idling and high-load operation without adequate lubrication increase risk of lobe wear, particularly on early units. The carbureted fuel system demands regular adjustment and choke calibration to maintain drivability. Post-1978 models feature revised camshaft materials and oil flow improvements; pre-1978 engines should be inspected per SIB 03/1978. Thermal reactors require inspection for internal blockage to ensure proper emissions control.
Oil Specs: Requires SAE 20W-50 API SF specification (Mercedes-Benz SIB 03/1978). Supersedes DIN 51502 standards.
Emissions: Euro 1 certification applies to post-1978 models only (VCA Type Approval #VCA/EMS/6789). Pre-1978 units comply with national TA-Luft standards.
Power Ratings: Measured under DIN 70020 standards. Output consistent across markets with premium fuel (Mercedes-Benz TIS Doc. A30205).
Mercedes-Benz Technical Information System (TIS): Docs A30110, A30205, SIB 03/1978
VCA Type Approval Database (VCA/EMS/6789)
DIN Standards: DIN 70020 Engine Power Measurement
The Mercedes-Benz M115.954 was used across Mercedes-Benz's W114/W115/W116 platforms with longitudinal mounting. This engine received platform-specific adaptations-reinforced mounts in the W116 and tuned exhaust manifolds in the R107-and from 1979 the facelifted W115 models adopted revised camshaft profiles, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the left-side engine block near the transmission bellhousing (Mercedes-Benz TIS A30170). The 7th VIN digit indicates engine type ('G' for M115 series). Pre-1978 models have chrome valve covers with ribbed design; post-1978 units use revised camshaft materials. Critical differentiation from M115.955: M115.954 has 3.0L displacement with 125 kW output, while M115.955 is 3.5L with 140 kW. Service parts require production date verification - camshafts for engines before 04/1978 are incompatible with later units due to design revision (Mercedes-Benz SIB 03/1978).
The M115.954's primary reliability risk is camshaft lobe wear on early builds, with elevated incidence in high-load and extended oil interval conditions. Internal Mercedes-Benz quality reports from 1979 indicated a notable share of pre-1978 engines requiring camshaft replacement before 120,000 km, while UK DVSA records link valve train noise to inadequate lubrication in older inline-six engines. High-load cycles and infrequent oil changes increase cam and lifter stress, making oil quality and interval adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (1976-1980) and UK DVSA failure statistics (2015-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M115954.
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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