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 including the E34 5 Series and E36 3 Series, the M50 B25 was engineered for responsive driving dynamics and smooth power delivery. Emissions compliance was achieved through catalytic converters and closed-loop lambda control, meeting European emissions standards (Euro 1–2), with the introduction of VANOS in 1992 improving low-end torque and idle stability.
One documented concern is oil leaks from the valve cover gasket and rear main seal, particularly on high-mileage units. This issue, while not critical, is prevalent due to the engine's aluminum construction and thermal cycling. Later revisions introduced improved gasket materials and revised sealing surfaces to enhance long-term reliability.
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 DOHC 24-valve design provides strong high-RPM power delivery ideal for spirited driving. Regular valve clearance checks every 30,000 km are essential to maintain performance and prevent valve train noise. Use of high-quality mineral or semi-synthetic 10W-40 oil meeting API SG/CC standards is recommended to ensure longevity of the timing chain and camshafts. Engines produced after 1992 benefit from VANOS, which improves low-end torque and idle quality but requires regular oil changes to prevent solenoid clogging. Cooling system maintenance is critical—verify thermostat function and hose integrity to prevent overheating.
Oil Specs: Requires SAE 10W-40, API SG/CC specification (BMW Service Manual 62-11-011). Supersedes earlier BMW oil standards.
Emissions: Euro 1 certification applies to pre-1993 models only (VCA Type Approval #VCA/EMS/5689). Euro 2 compliance confirmed for 1993–1996 production.
Power Ratings: Measured under DIN 70020 standards. Output consistent across all markets with proper maintenance.
BMW Technical Information System (TIS): Docs A24580, A24733
VCA Type Approval Database (VCA/EMS/5689)
DIN 70020:2004 - Road vehicles — Engine power — Measurement
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.
Locate the engine code stamped horizontally on the front-facing surface of the cylinder block, near the exhaust manifold (BMW TIS A24580). The 7th VIN digit indicates engine family ('M' for M50 series). Pre-1992 models lack VANOS and have a simpler intake manifold; post-1992 units feature VANOS solenoids on the camshaft covers. Critical differentiation from M50B20: M50B25 has longer stroke (75.0 mm vs 66.0 mm) and greater displacement. Service parts require model-year verification—intake manifolds and timing covers differ between E34 and E36 applications (BMW TIS A24624).
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.
Find answers to most commonly asked questions about BMW M50B25-256S2.
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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