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 p…
Models from 1986–1988 meet Euro 1 emissions standards .
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 | Refer to vehicle handbook / manufacturer specification | |
Dry weight | 185 kg |
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.
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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.
The most common questions about engine codes, what they mean, how to find them and how this database works
Yes. The M30 B25 is mechanically robust and known for longevity when properly maintained. Its electronic fuel injection is more reliable than carburetors, and the inline-six design is inherently smooth and durable. Regular oil changes, cooling system service, and attention to the fuel system ensure decades of reliable operation. Many examples exceed 200,000 km with basic maintenance.
The most common issues are L-Jetronic fuel injection drift, vacuum leaks, and cooling system failures due to age. Oil leaks from the valve cover and rear main seal are also frequent in high-mileage engines. These are well-documented in BMW service bulletins and classic car maintenance guides.
This 2.5L petrol was used in the E12 5 Series (525) from 1977–1981, the E24 6 Series (625) from 1977–1987, and the E28 5 Series (525e, 525i) from 1981–1988. It was phased out with the introduction of the M50 engine family. All late models (1986–1988) meet Euro 1 emissions with catalytic converters.
Aftermarket ECU tuning is common on the M30B25 platform, but increasing boost or altering engine parameters accelerates component wear, impacts emissions compliance, and may void vehicle warranties. Any modifications should be evaluated carefully by a qualified specialist.
Moderate for its era. In a BMW 525i (E28) from 1985, typical consumption is ~11.0 L/100km (city) and ~7.0 L/100km (highway), or about 30 mpg UK combined. Real-world figures depend on driving style and condition, but expect 27-32 mpg (UK) for a well-tuned example.
No. The M30 B25 is a non-interference engine. If the timing chain fails, the pistons will not strike the valves, preventing catastrophic internal damage. This adds to its reputation for durability and makes timing maintenance less critical than on modern engines.
BMW recommends SAE 10W-40 mineral oil for older models or 5W-40 synthetic for year-round use. Change oil every 7,500–10,000 km. Use high-quality oil meeting API SL/CF standards to protect the timing chain and hydraulic lifters.
Comprehensive technical documentation and regulatory references
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Regulatory Stability
EU regulations are referenced using CELEX identifiers for long-term stability.
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
Type-approval guidance and documentation.
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