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…
Production years 1983–1991 meet Euro 0 to Euro 1 standards .
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 | Refer to vehicle handbook / manufacturer specification | |
Dry weight | 205 kg |
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.
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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.
The most common questions about engine codes, what they mean, how to find them and how this database works
The M21 D24 (246TB) is highly reliable when properly maintained. Its simple mechanical design and robust construction make it one of BMW's most durable engines. Common issues like injection pump wear and cooling system failures are manageable with routine care. With regular oil changes, coolant service, and valve adjustments, these engines can exceed 200,000 km with minimal major repairs.
The most common issues are fuel injection pump wear, cooling system failures (radiator, thermostat, water pump), intake manifold gasket leaks, and valve stem seal degradation. These are well-documented in factory service literature and are largely preventable with proper maintenance, use of quality diesel, and regular inspection of fuel and cooling components.
This 2.4L diesel was used in the BMW 5 Series (E28: 524d, 1983–1988) and 3 Series (E30: 324d, 1987–1991). All applications feature longitudinal engine mounting and were built to meet early Euro emissions standards.
Yes, the M21 D24 responds well to classic tuning. Common upgrades include performance fuel injection pumps, exhaust headers, and upgraded intake manifolds. With these modifications, outputs of 90–100 PS are achievable. Turbocharging conversions are also possible but require significant engineering. Tuning should respect the engine's mechanical limits, particularly the stock crankshaft and connecting rods.
Excellent for its era. In a BMW 524d (E28), real-world consumption averages 7.5–9.0 L/100km (31–37 mpg UK) on mixed driving. Highway efficiency can reach ~6.5 L/100km (~43 mpg UK). Actual economy depends on driving style and engine condition, but it offers a good balance of performance and efficiency for a naturally aspirated diesel inline-six engine.
No. The M21 D24 is a non-interference engine. If the timing chain fails or jumps, piston-to-valve contact will not occur, preventing catastrophic internal damage. This design feature enhances its reliability and makes it a popular choice for restorers and classic car enthusiasts.
BMW originally specified SAE 10W-40 mineral or semi-synthetic oil. Modern high-quality mineral or semi-synthetic oils meeting this viscosity are suitable. Oil should be changed every 10,000–15,000 km or annually to ensure proper lubrication of the timing chain and valvetrain.
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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