The M20B25 – 2.5 liter engine without catalytic converter. It was originally released with a carburetor, and over time it was equipped with a fuel injection system – Bosch. The engine management system was used by Bosch Motronic 1.1/1.3. In 1987, the B25 was upgraded after which the capacity was increased.
In 1987, a catalyzed model with Motronic 1.3 engine management was introduced. The compression ratio was reduced to 8.8:1 but thanks to the more sophisticated electronics power remained nearly as before, at 125 kW (170 PS; 168 hp). The uncatalyzed engine was kept in production for Southern Europe and other markets where unleaded petrol was not regularly available.
Specifications
| Manufacturer | Munich Plant |
| Family | M20 |
| Production years | 1986-1993 |
| Cylinder block alloy | cast iron |
| Fuel system | injector |
| Configuration | inline |
| Number of cylinders | 6 |
| Valves per cylinder | 2 |
| Piston stroke, mm | 75 |
| Cylinder bore, mm | 84 |
| Compression ratio | 9.7 9.7 8.8 |
| Displacement, cc | 2494 |
| Power output, hp | 163/5800 171/5800 170/5800 |
| Torque output, Nm / rpm | 215/4000 226/4000 222/4300 |
| Fuel type | petrol |
| Weight, kg | ~117 (dry) |
| Fuel consumption, L/100 km (for E30 325i) — city — highway — combined |
12.9 7.2 9.0 |
| Oil consumption, gr/1000 km | up to 1000 |
| Recommended engine oil | 5W-30 / 5W-40 / 10W-30 / 10W-40 / 10W-50 / 15W-40 / 15W-50 |
| Engine oil capacity, liter | 4.75 |
| Normal engine operating temperature, °C | ~90 |
| Engine lifespan, km | ~300 000 |
Frequent problems
- Temperature rise. Due to a malfunction in the cooling system, the cylinder head overheats and leads. Check for air blockages, general condition of the radiator, thermostat and pump functionality.
- Camshaft pastels worn out. A characteristic feature is the knock of the camshaft when passing more than 200 thousand km. Repair – installation of a new cylinder head.
- The cylinder head is cracked. Typical ailment M20. The reason is overheating. The crack usually occurs between the 4th and 5th cylinder. Cylinder head needs to be replaced.
In the M20B25 unit, the condition of the timing belt and the condition of its tensioner roller also needs a thorough inspection. If the belt breaks, the valve bends cannot be avoided, and sometimes even the complete destruction of the pistons. As they age (it should be borne in mind that they have been produced since 1986), the engines of this series exhibit characteristic aging defects. For this reason, buying a car equipped with this unit is not a very promising undertaking, in terms of its trouble-free further service.
