The BMW M21D24 (246DB) is a 2,443 cc inline — six diesel engine, part of BMW’s first — generation diesel engine family introduced in 1983. It features a single overhead camshaft (SOHC) design with a belt — driven valvetrain, mechanical Bosch VE — type rotary injection pump, and a compression ratio of 22.0:1. Producing 86 bhp (64 kW) at 4,600 rpm and 180 Nm of torque at 2,400 rpm, it was engineered for durability, fuel efficiency, and smooth operation in BMW’s luxury sedans and to…
The M21D24 (246DB) predates formal Euro emissions standards, complying with German TÜV and EU type-approval regulations applicable to vehicles produced between 1985 and 1991 (EU Directive 70/220/EEC, amended).
The BMW M21D24 (246DB) is a 2,443 cc SOHC inline-six turbocharged diesel engine produced from 1983 to 1991, primarily for the E28 and E34 5 Series. It features a mechanical Bosch VE rotary injection pump and belt-driven camshaft, delivering proven mechanical durability and strong low-RPM torque. Designed before modern emissions regulations, it represents BMW’s pioneering effort in diesel passenger car technology.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,443 cc | |
Fuel type | Diesel | |
Configuration | Inline-6, SOHC, 12-valve | |
Aspiration | Turbocharged | |
Bore × stroke | 84.0 mm × 73.5 mm | |
Power output | 86 bhp (64 kW) @ 4,600 rpm | |
Torque | 180 Nm @ 2,400 rpm | |
Fuel system | Bosch VE-type rotary injection pump | |
Emissions standard | Pre-regulatory (EU Directive 70/220/EEC) | |
Compression ratio | 22.0:1 | |
Cooling system | Water-cooled | |
Turbocharger | KKK K26-2 turbocharger | |
Timing system | Single-row timing belt | |
Oil type | Refer to vehicle handbook / manufacturer specification | |
Dry weight | 180 kg |
The BMW M21D24 (246DB) was used in the E28 and E34 5 Series platforms with longitudinal mounting and rear-wheel drive. It was paired with a 5-speed manual transmission (Getrag 260). No platform-specific tuning or emissions variants were produced. The M21D24 (246DB) was succeeded by the electronically injected M51D25 in the E34 generation. All data is documented in OEM service manuals and parts catalogues.
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The M21D24 (246DB)'s primary reliability risk is timing belt failure due to age or neglect, which can result in bent valves due to its interference design. While the engine block and crankshaft are highly durable, injection pump wear, turbocharger oil leaks, and valve stem seal degradation are common in high-mileage or poorly maintained examples. UK DVLA MOT failure data from 2020–2023 indicates that 25% of E34 524td models fail due to smoke emissions or excessive oil consumption, often linked to turbo or valve guide issues. Adherence to maintenance schedules and use of quality replacement parts are critical for long-term operation.
Analysis derived from BMW technical bulletins (1983–1991), ETK parts documentation, and UK DVLA MOT failure statistics (2020–2023). Repair procedures should follow manufacturer guidelines.
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Yes, the M21D24 (246DB) is mechanically robust and capable of high mileage when properly maintained. Its SOHC design and durable cast-iron block contribute to longevity. The critical maintenance item is the timing belt, which must be replaced every 60,000 km to prevent catastrophic valve damage. With regular oil changes, injection pump servicing, and attention to cooling system health, the engine can reliably exceed 300,000 km.
Key issues include timing belt failure (due to its interference design), injection pump wear causing drivability problems, turbocharger oil leaks leading to smoke emissions, and valve stem seal wear causing oil consumption. These are age-related rather than design flaws and are largely preventable with proper maintenance and use of quality replacement parts.
The M21D24 (246DB) was used in the BMW 5 Series (E28) 524td model from 1985 to 1988 and the 5 Series (E34) 524td from 1988 to 1991. It was the first turbocharged diesel engine for this generation and was not offered in any other BMW or MINI model. The engine was succeeded by the M51D25 in later E34 models.
Yes, but within limits. The M21D24 (246DB) can be modified with a performance intercooler, upgraded exhaust manifold, and tuned injection pump to gain 10–15 bhp. However, the stock turbocharger and mechanical fuel system limit high-RPM potential. Some enthusiasts convert to electronic injection using an M51 intake manifold and ECU, but this is complex. Over-fueling without proper cooling can lead to reliability issues.
In the E34 524td, the M21D24 (246DB) achieves approximately 6.5–7.5 L/100km (~43–37 mpg UK) in mixed driving. Highway economy can reach 6.0 L/100km (~47 mpg UK), while city driving may exceed 8.5 L/100km (~33 mpg UK). Its mechanical injection and turbocharging provide excellent fuel efficiency for a six-cylinder diesel.
Yes. The M21D24 (246DB) is an interference engine. If the timing belt fails or jumps timing, the pistons will contact the open valves, resulting in bent valves and potentially severe internal damage. This is why strict adherence to the 60,000 km timing belt replacement interval is critical.
BMW recommends SAE 15W-40 mineral oil for the M21D24 (246DB), suitable for the engine's hydraulic lifters and camshaft. Oil changes should occur every 10,000 km or annually. Modern API CF-4 15W-40 oils are compatible and provide adequate protection for both classic and restored applications.
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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