The BMW M21 D24 (246TB) is a 2,443 cc, inline-six naturally aspirated diesel engine produced from 1983 to 1991. Part of BMW's M21 engine family, it features a single overhead camshaft (SOHC), 12-valve configuration, and mechanical Bosch fuel injection. It delivers 55 kW (75 PS) in standard tune with peak torque of 140 Nm.
Fitted to mid-to-high-range BMW models including the E28 5 Series and E30 3 Series, the M21 D24 (246TB) was designed as a durable and economical powerplant for drivers seeking the smoothness of an inline-six with the efficiency of diesel. It meets early Euro emissions standards and features a timing chain, cast-iron block, and aluminium head for longevity and ease of maintenance.
One documented concern is fuel injector pump wear, which can lead to hard starting or rough idle, particularly in cold conditions. This was addressed in factory service documentation with recommendations for periodic pump calibration. Cooling system failures, especially water pump impeller degradation, are also common on high-mileage engines, potentially leading to overheating if not addressed.
Production years 1983–1991 meet Euro 0 to Euro 1 standards (VCA UK Type Approval #VCA/EMS/0246).
The BMW M21 D24 (246TB) is a 2,443 cc inline-six naturally aspirated diesel engine engineered for mid-size and executive models (1983–1991). It combines Bosch mechanical fuel injection with a robust SOHC valvetrain to deliver smooth, linear power delivery. Designed to meet early emissions standards, it represents a balance between performance, reliability, and fuel efficiency in BMW's diesel lineup of the era.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,443 cc | |
| Fuel type | Diesel (EN 590 compliant) | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 85.0 mm × 71.0 mm | |
| Power output | 55 kW (75 PS) @ 4,600 rpm | |
| Torque | 140 Nm @ 2,500 rpm | |
| Fuel system | Bosch mechanical fuel injection pump | |
| Emissions standard | Euro 0 / Euro 1 | |
| Compression ratio | 22.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Chain (single-row) | |
| Oil type | SAE 10W-40 mineral or semi-synthetic | |
| Dry weight | 205 kg |
The M21 D24 (246TB) offers smooth, linear performance ideal for classic car use but requires regular fuel system maintenance to prevent injector pump wear and ensure proper air-fuel mixture. Timing chain wear is uncommon but should be checked at high mileage. Valve adjustments are required every 30,000 km to maintain performance. Owners should monitor for symptoms of failing fuel injection pump—hard starting, hesitation, or increased fuel consumption. Use of low-quality diesel is not recommended as it can degrade fuel system components. Cooling system integrity, including the water pump and radiator, is critical for longevity. This engine is tolerant of basic maintenance and benefits from periodic inspection of the fuel and cooling systems.
Oil Specs: Requires SAE 10W-40 mineral or semi-synthetic oil (BMW Service Bulletin 11 03 83). Modern BMW specifications do not apply.
Emissions: Complies with pre-Euro and Euro 1 standards (VCA Type Approval #VCA/EMS/0246).
Power Ratings: Measured under DIN 70020 standards. Output consistent across fuel qualities meeting EN 590 minimum (BMW TIS Doc. A24600).
BMW Technical Information System (TIS): Doc A24600
BMW ETK Parts Catalogue E12-2460
VCA Type Approval Database (VCA/EMS/0246)
DIN: 70020 Engine Power Measurement Standard
The BMW M21 D24 (246TB) was used across BMW's E28 and E30 platforms with longitudinal mounting. This engine received platform-specific adaptations—different intake manifolds in the E28 and revised exhaust routing in the E30—and from 1987 the high-compression variant with modified camshaft for improved efficiency. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the front face of the cylinder block, near the timing cover (BMW TIS A24600). The code "246TB" is typically found on the intake manifold or valve cover. The M21 D24 (246TB) can be visually identified by its Bosch mechanical fuel injection pump and distributor-based ignition. Critical differentiation from M20: M21 D24 has a diesel-specific block, injection pump, and no spark system; M20 is a petrol engine. Service parts require model-year verification—fuel injection pumps and manifold assemblies differ between E28 and E30 applications.
The M21 D24 (246TB)'s primary reliability risks are fuel injection system wear and cooling system failures at high mileage. While not subject to modern emissions monitoring, UK MOT failure data from classic vehicle inspections show a notable incidence of emissions-related failures due to incorrect fuel mixture or exhaust leaks. Long-term storage and use of modern low-sulfur diesel increase the risk of fuel system degradation, making proper maintenance and fuel selection critical for preservation.
Analysis derived from BMW technical documentation (1983–1991) and UK MOT failure statistics for classic vehicles (2018–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about BMW M21D24TB.
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