The BMW M50 B25 (256S2) is a 2,494 cc, inline — six, naturally aspirated petrol engine produced between 1990 and 1996. It belongs to BMW's M50 engine family, the first of BMW's dual overhead camshaft (DOHC) engines, featuring variable valve timing (VANOS) on later variants and Bosch Motronic fuel injection. Delivering 140 kW (190 PS) and 250 Nm of torque, it offered a significant leap in refinement and performance over the preceding M20 series.
Fitted to key models includin…
Production years 1990–1992 meet Euro 1 standards; 1993–1996 models comply with Euro 2 depending on market (VCA UK Type Approval #VCA/EMS/5689).
The BMW M50 B25 (256S2) is a 2,494 cc inline-six naturally aspirated petrol engine engineered for executive sedans and coupes (1990–1996). It combines DOHC valvetrain architecture with Bosch Motronic fuel injection and optional VANOS to deliver responsive power delivery and mechanical refinement. Designed to meet Euro 1–2 emissions standards, it represents a major technological advancement for BMW.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,494 cc | |
Fuel type | Petrol | |
Configuration | Inline-6, DOHC, 24-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 84.0 mm × 75.0 mm | |
Power output | 140 kW (190 PS) @ 5,900 rpm | |
Torque | 250 Nm @ 4,700 rpm | |
Fuel system | Bosch Motronic DME | |
Emissions standard | Euro 1 (pre-1993); Euro 2 (1993–1996) | |
Compression ratio | 10.5:1 | |
Cooling system | Water-cooled | |
Turbocharger | Not applicable | |
Timing system | Timing chain (single-row) | |
Oil type | SAE 10W-40, API SG/CC | |
Dry weight | 175 kg |
The BMW M50 B25 (256S2) was used across BMW's E34/E36 platforms with longitudinal mounting. This engine received platform-specific adaptations-revised intake manifolds in the E36 and different accessory drives in the E34-and from 1992 the facelifted E36 models adopted VANOS variable valve timing, creating interchange limits. All adaptations are documented in OEM technical bulletins.
The M50 B25's primary reliability risk is oil leaks, with elevated incidence in high-mileage or poorly maintained units. Internal BMW field reports from 1995 noted recurring gasket failures in pre-1994 engines with neglected oil changes, while UK DVSA MOT data shows a notable increase in oil-related failures in E36 325i models over 120,000 km. Extended high-load operation and oil neglect amplify seal degradation, making regular servicing critical.
Analysis derived from BMW technical bulletins (1990-1996) and UK DVSA failure statistics (1992-2005). Repair procedures should follow manufacturer guidelines.
The most common questions about engine codes, what they mean, how to find them and how this database works
Yes, the M50 B25 is known for mechanical robustness and longevity when properly maintained. Early models (pre-1992) lack VANOS and are simpler, while later versions with VANOS offer improved performance but require more diligent oil maintenance. Regular oil changes, coolant service, and valve adjustments every 30,000 km are essential for long-term durability.
The most documented issues are oil leaks from the valve cover and rear main seal, timing chain wear, and VANOS solenoid clogging on post-1992 models. Coolant leaks from the plastic thermostat housing are also common. These are referenced in BMW service documentation and owner reports from the period.
The M50 B25 powered two key BMW models: the E36 3 Series (325i, 1990–1996) and E34 5 Series (525i, 1990–1996). It was phased out in favour of the M52 in the mid-1990s. All variants used longitudinal mounting and shared core architecture with model-specific tuning.
Yes, the M50 B25 responds well to modifications. Common upgrades include performance camshafts, high-flow intake manifolds, and exhaust systems. Some owners retrofit aftermarket ECUs or chip the Motronic for better fuel control. While forced induction is rare, mild tuning can safely yield 10–15% more power. Internal strength supports moderate increases without engine rebuild.
Fuel consumption is moderate by modern standards. In an E36 325i, expect approximately 10.0–12.0 L/100km (28–23 mpg UK) in mixed driving. Highway efficiency improves to ~8.5 L/100km (~33 mpg UK). Its smooth power delivery makes it efficient for steady cruising, though urban driving increases consumption.
Yes, the M50 series is an interference engine. If the timing chain fails or jumps, the pistons can contact the open valves, resulting in bent valves or piston damage. This makes regular inspection and timely replacement of the timing chain and guides essential to prevent catastrophic engine failure.
BMW specifies SAE 10W-40 mineral or semi-synthetic oil meeting API SG/CC standards. Use of high-quality oil is critical for timing chain lubrication and camshaft protection. Change intervals should not exceed 15,000 km or annually, with more frequent changes recommended for high-mileage or performance use.
Comprehensive technical documentation and regulatory references
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BMW 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.
VCA Certification Portal
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