The BMW M30 B25 is a 2,494 cc, inline-six naturally aspirated petrol engine introduced in 1977 as part of BMW's long-running M30 engine family. It features a cast-iron block, aluminium head, single overhead camshaft (SOHC), and Bosch L-Jetronic electronic fuel injection. In standard tune it delivers 105–110 kW (143–150 PS), with torque output of 210 Nm, offering smooth and refined performance typical of BMW's inline-six heritage.
Fitted across BMW's E12, E24, and E28 platforms, the M30 B25 was engineered for longitudinal mounting and rear-wheel drive layouts. Emissions compliance was achieved through early catalytic converter systems in later models, meeting Euro 1 standards from 1986. The engine is renowned for its durability and mechanical simplicity, supporting decades of enthusiast ownership and restoration.
One documented concern is fuel injector clogging and airflow meter drift in older units due to aging components and modern fuel chemistry. This issue, referenced in BMW Service Information Bulletin 13 07 87, is linked to varnish buildup in L-Jetronic injectors and degraded airflow sensor seals. From 1985, BMW revised fuel system calibration and introduced improved sealing components to enhance long-term reliability.
Models from 1986–1988 meet Euro 1 emissions standards (VCA UK Type Approval #VCA/EMS/7896).
The BMW M30 B25 is a 2,494 cc inline-six naturally aspirated petrol engine engineered for executive sedans and grand tourers (1977–1988). It combines electronic fuel injection with a smooth inline-six design to deliver linear power delivery and driver engagement. Designed to meet evolving emissions standards, it balances refinement with mechanical reliability and serviceability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,494 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 80.0 mm × 78.0 mm | |
| Power output | 105–110 kW (143–150 PS) @ 5,800 rpm | |
| Torque | 210 Nm @ 3,500 rpm | |
| Fuel system | Bosch L-Jetronic electronic fuel injection | |
| Emissions standard | Euro 1 (1986–1988) | |
| Compression ratio | 9.0:1 – 9.5:1 | |
| Cooling system | Water-cooled with mechanical thermostat | |
| Turbocharger | None | |
| Timing system | Chain (single-row, front-mounted) | |
| Oil type | SAE 10W-40 mineral or 5W-40 synthetic | |
| Dry weight | 185 kg |
The M30 B25's L-Jetronic fuel injection system offers improved drivability over carbureted variants but requires attention to aging sensors and fuel quality. The system is sensitive to vacuum leaks, degraded airflow meters, and clogged injectors, which can cause idle instability and poor fuel economy. Oil changes every 7,500–10,000 km are recommended to maintain chain and bearing longevity. From 1986, catalytic converters were fitted to meet Euro 1 standards, requiring unleaded fuel. Timing chain wear is uncommon but possible in neglected engines; inspection is advised during major service. The engine tolerates lower-octane fuel but performs best on 95 RON. Modern ethanol-blended fuels can degrade old rubber components; use ethanol-compatible hoses for long-term reliability.
Oil Specs: No BMW Longlife specification; use high-quality mineral or synthetic 10W-40 meeting API SL/CF standards (BMW SIB 13 07 87).
Emissions: Euro 1 certification applies to 1986–1988 models (VCA Type Approval #VCA/EMS/7896). Pre-1986 models are non-catalyst.
Power Ratings: Measured under DIN 70020 standards. Output varies by model year and market (BMW TIS Doc. A20005).
BMW Technical Information System (TIS): Docs A20000, A20001, A20002, SIB 13 07 87
VCA Type Approval Database (VCA/EMS/7896)
DIN Deutsches Institut für Normung: DIN 70020 Power Measurement Standard
The BMW M30 B25 was used across BMW's E12, E24, and E28 platforms with longitudinal mounting and RWD layout. This engine received platform-specific adaptations—revised intake manifolds in the E28 and dual-exhaust setup in performance variants—and from 1986 the facelifted E28 models adopted catalytic converters to meet Euro 1, creating interchange limits. No licensed or shared-production partnerships existed for this engine. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the front timing cover near the oil filter housing (BMW TIS A20010). The 7th VIN digit indicates engine family ('M' for M-series). All M30 B25 units use Bosch L-Jetronic fuel injection with a prominent airflow meter. E28 models (1981–1988) have revised valve covers and intake plumbing. Critical differentiation: This variant is an inline-six with 2.5L displacement and is specific to 525 and 625 models. Service parts are generally interchangeable, but catalytic converter-equipped models (post-1986) require compatible exhaust manifolds.
The M30 B25's primary concerns are age-related: fuel system degradation, vacuum leaks, and cooling system failures. UK DVLA and MOT records indicate that poorly maintained examples often fail on emissions or idle quality, while well-serviced engines regularly exceed 200,000 km. Cold-start performance and idle stability are most affected by neglected fuel and ignition systems.
Analysis derived from BMW technical bulletins (1980s), UK DVSA MOT failure statistics (2018-2024), and restoration guides. Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about BMW M30B25.
Comprehensive technical documentation and regulatory references
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EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
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DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
Vehicle Certification Agency (VCA)
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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.
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