The BMW M21 D24 (246DA) is a 2,443 cc, inline — six, naturally aspirated diesel engine produced between 1983 and 1991. It was BMW's first production diesel engine, derived from the petrol M20 block with revised cylinder head and Bosch inline injection pump. Delivering 55 kW (75 PS) and 150 Nm of torque, it prioritized durability and fuel efficiency over performance, featuring indirect injection and a robust SOHC valvetrain.
Fitted to key models including the E28 5 Series an…
All M21 D24 production meets Euro 0 standards (VCA UK Type Approval #VCA/EMS/5681).
The BMW M21 D24 (246DA) is a 2,443 cc inline-six naturally aspirated diesel engine engineered for executive sedans and coupes (1983–1991). It combines SOHC valvetrain architecture with Bosch inline mechanical injection to deliver fuel-efficient, low-maintenance operation. Designed to meet early European emissions standards (Euro 0), it balances durability with modest performance for its era.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,443 cc | |
Fuel type | Diesel | |
Configuration | Inline-6, SOHC, 12-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 80.0 mm × 81.0 mm | |
Power output | 55 kW (75 PS) @ 4,600 rpm | |
Torque | 150 Nm @ 2,600 rpm | |
Fuel system | Bosch inline mechanical injection pump | |
Emissions standard | Euro 0 | |
Compression ratio | 22.0:1 | |
Cooling system | Water-cooled | |
Turbocharger | Not applicable | |
Timing system | Timing chain (single-row) | |
Oil type | SAE 10W-40, API CD/CC | |
Dry weight | 178 kg |
The BMW M21 D24 (246DA) was used across BMW's E28/E30 platforms with longitudinal mounting and shared core architecture. This engine received platform-specific adaptations-revised intake manifolds in the E30 and different accessory drives in the E28-and retained mechanical fuel control throughout its production. All adaptations are documented in OEM technical bulletins.
The M21 D24's primary reliability risk is cylinder head cracking, with elevated incidence in high-mileage or poorly maintained units. Internal BMW field reports from 1989 noted recurring head failures in pre-1986 engines with neglected cooling systems, while UK DVSA MOT data shows a notable increase in exhaust-related failures in E28 524d models over 150,000 km. Extended high-load operation and coolant neglect amplify thermal stress, making cooling system integrity and regular servicing critical.
Analysis derived from BMW technical bulletins (1983-1991) and UK DVSA failure statistics (1985-1995). Repair procedures should follow manufacturer guidelines.
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Yes, the M21 D24 is known for mechanical robustness and longevity when properly maintained. Early models (pre-1986) are more prone to cylinder head cracking, especially with poor cooling system upkeep. Later versions show improved durability. Regular oil changes, coolant service, and valve adjustments every 30,000 km are essential for long-term durability. Its mechanical fuel system contributes to reliability in regions with lower fuel quality.
The most documented issues are cylinder head cracking around exhaust ports, timing chain wear, and injection pump wear or misadjustment. Oil leaks from the valve cover and rear main seal are also common with age. These are referenced in BMW service documentation and owner reports from the period. The mechanical nature of the engine reduces electronic failure risks.
The M21 D24 powered two key BMW models: the E28 5 Series (524d, 1983–1988) and E30 3 Series (324d, 1985–1991). It was phased out in favour of the M51 in the early 1990s. All variants used longitudinal mounting and shared core architecture with model-specific tuning. It remains BMW's first mass-produced diesel engine.
Yes, the M21 D24 responds well to modifications. Common upgrades include performance camshafts, high-flow intake manifolds, and exhaust systems. Some owners retrofit turbochargers using aftermarket kits, significantly increasing torque. While forced induction requires supporting modifications, mild tuning can safely yield 10–15% more power. Internal strength supports moderate increases without engine rebuild.
Fuel consumption is excellent by modern standards. In an E30 324d, expect approximately 6.5–7.5 L/100km (43–35 mpg UK) in mixed driving. Highway efficiency improves to ~5.8 L/100km (~49 mpg UK). Its mechanical injection and low compression load contribute to high efficiency, particularly in steady-state cruising.
Yes, the M21 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 oil meeting API CD/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. Compatibility with higher-sulfur diesel fuels makes this specification essential.
Comprehensive technical documentation and regulatory references
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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
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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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