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 and E30 3 Series, the M21 D24 was engineered for economical long-distance driving and fleet applications. Emissions compliance was achieved through basic combustion tuning and exhaust gas recirculation (EGR) on later models, meeting early European standards (Euro 0), with its mechanical fuel system requiring minimal electronics for reliable operation.
One documented concern is cylinder head cracking, particularly around the exhaust ports, which can develop due to thermal stress in high-load conditions. This issue, referenced in BMW Technical Service Bulletin 11 51 85, is more prevalent in engines with inconsistent cooling system maintenance. Later revisions introduced improved casting techniques and revised coolant flow paths to mitigate thermal gradients.
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 naturally aspirated design provides linear power delivery and excellent fuel economy under steady loads, ideal for highway cruising. Regular valve clearance checks every 30,000 km are essential to maintain performance and prevent valve train noise. Use of high-quality mineral oil meeting API CD/CC standards is recommended to ensure longevity of the timing chain and camshaft. Cylinder head integrity should be monitored, especially in high-mileage units, as thermal stress can lead to exhaust port cracks. The mechanical injection system is highly durable but requires periodic pump calibration. Cooling system maintenance is critical—verify thermostat function and hose integrity to prevent overheating and head warping.
Oil Specs: Requires SAE 10W-40, API CD/CC specification (BMW Service Manual 62-11-004). Formulated for high-sulfur diesel compatibility.
Emissions: Certified to Euro 0 across entire production run (VCA Type Approval #VCA/EMS/5681). No Euro 1 variants produced.
Power Ratings: Measured under DIN 70020 standards. Output consistent across all markets with proper maintenance.
BMW Technical Information System (TIS): Docs A24573, A24726, SIB 11 51 85
VCA Type Approval Database (VCA/EMS/5681)
DIN 70020:2004 - Road vehicles — Engine power — Measurement
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.
Locate the engine code stamped horizontally on the front-facing surface of the cylinder block, near the exhaust manifold (BMW TIS A24573). The 7th VIN digit indicates engine family ('M' for M21 series). All M21 D24 units feature a Bosch inline mechanical injection pump with manual throttle linkage. Critical differentiation from M20B25: M21 D24 has taller block with longer stroke (81.0 mm vs 72.6 mm), visible via sump profile and lack of ignition system. Service parts require model-year verification—timing covers and intake manifolds differ between E28 and E30 applications (BMW TIS A24614).
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.
Find answers to most commonly asked questions about BMW M21D24.
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