The BMW M20 B23 (236EC) is a 2,316 cc, inline-six, naturally aspirated petrol engine produced between 1983 and 1988. It belongs to BMW's M20 engine family, known for smoothness and durability, featuring a single overhead camshaft (SOHC) and Bosch Motronic fuel injection. Delivering 105 kW (143 PS) and 200 Nm of torque, it offered refined performance ideal for mid-size executive sedans and coupes of the era.
Fitted to key models including the E28 5 Series and E30 3 Series, the M20 B23 was engineered to balance responsive power delivery with long-term reliability. Emissions compliance was achieved through catalytic converters and closed-loop lambda control, meeting early European emissions standards (Euro 0–1), with Motronic-equipped variants offering improved fuel metering and reduced hydrocarbon emissions.
One documented concern is cylinder head cracking, particularly around the exhaust ports, which can develop due to repeated thermal cycling. This issue, referenced in BMW Technical Service Bulletin 11 51 85, is more prevalent in high-mileage or poorly maintained engines. Later revisions of the M20 series introduced improved head casting techniques and revised cooling system routing to mitigate thermal stress.
Production years 1983–1986 meet Euro 0 standards; 1987–1988 models comply with Euro 1 depending on market (VCA UK Type Approval #VCA/EMS/5679).
The BMW M20 B23 (236EC) is a 2,316 cc inline-six naturally aspirated petrol engine engineered for executive sedans and coupes (1983–1988). It combines SOHC valvetrain architecture with Bosch Motronic fuel injection to deliver smooth power delivery and mechanical refinement. Designed to meet early European emissions standards (Euro 0–1), it balances responsive performance with long-term durability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,316 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 80.0 mm × 72.6 mm | |
| Power output | 105 kW (143 PS) @ 5,500 rpm | |
| Torque | 200 Nm @ 4,200 rpm | |
| Fuel system | Bosch Motronic DME | |
| Emissions standard | Euro 0 (pre-1987); Euro 1 (1987–1988) | |
| Compression ratio | 9.8:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Timing chain (single-row) | |
| Oil type | SAE 10W-40, API SF/CC | |
| Dry weight | 167 kg |
The inline-six configuration provides smooth power delivery and inherent balance, ideal for relaxed cruising and spirited driving. Regular valve clearance checks every 30,000 km are essential to maintain performance and prevent valve train noise. Use of high-quality mineral or semi-synthetic 10W-40 oil meeting API SF/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. Motronic-equipped models benefit from more precise fuel metering and improved cold-start behaviour. Cooling system maintenance is critical—verify thermostat function and hose integrity to prevent overheating and head warping.
Oil Specs: Requires SAE 10W-40, API SF/CC specification (BMW Service Manual 62-11-002). Supersedes earlier BMW oil standards.
Emissions: Euro 0 certification applies to pre-1987 models only (VCA Type Approval #VCA/EMS/5679). Euro 1 compliance confirmed for 1987–1988 production.
Power Ratings: Measured under DIN 70020 standards. Output consistent across fuel-injected variants with proper maintenance.
BMW Technical Information System (TIS): Docs A24571, A24724, SIB 11 51 85
VCA Type Approval Database (VCA/EMS/5679)
DIN 70020:2004 - Road vehicles — Engine power — Measurement
The BMW M20 B23 (236EC) 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 from 1987 the facelifted E30 models adopted updated Motronic DME systems, creating interchange limits. 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 A24571). The 7th VIN digit indicates engine family ('M' for M20 series). All M20 B23 units feature Bosch Motronic DME with integrated control unit. Critical differentiation from M20B20: M20B23 has longer stroke (72.6 mm vs 66.0 mm) and larger displacement. Service parts require model-year verification—intake manifolds and timing covers differ between E28 and E30 applications (BMW TIS A24611).
The M20 B23's primary reliability risk is cylinder head cracking, with elevated incidence in high-mileage or poorly maintained units. Internal BMW field reports from 1988 noted recurring head failures in pre-1985 engines with neglected cooling systems, while UK DVSA MOT data shows a notable increase in exhaust-related failures in E28 523i 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 (1983-1988) and UK DVSA failure statistics (1985-1995). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about BMW M20B23.
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