M20B25 is a 2.5 L inline-six, 4-cycle naturally aspirated gasoline engine, built on the framework of the M20B20 2.0L motor. Being a part of the series of BMW M20 motors, it was built between 1985 and 1991 at the company’s plant in Munich.
This motor keeps a block of cast iron and head of aluminum with an overhead camshaft and two valves in each of six cylinders. The sizes of the cylinder bore and piston stroke are 84.0 mm (3.31 inches) and 75.0 mm (2.95 inches) correspondingly. Fuel injection is Bosch Motronic 1.1/1.3 Adaptive.
In 1985-1986, the first modifications of the motor featured Bosch Motronic 1.1 injection. The compression index was 9.7:1 while a redline was 6,500 rpm. The capacity was equal to 169 hp at 5,800 rpm and a torque of 226 Nm (23.0 kg-m; 166.8 ft-lb) at 4,000 rpm.
By 1987, the motor was modified with the addition of Motronic 1.3. The compression rate descended to 9.3:1. The motor’s output was 169 hp at 5,800 rpm. Moreover, the motor had a modification with catalytic converters. The compression index was 8.8:1 while the capacity was 168 hp at 5,800 rpm and a torque of 222 Nm (22.6 kg-m; 163.8 ft-lb) at 4,300 rpm.
M20B25 Engine Specs
| Manufacturer | Gunma Oizumi Plant |
| Also called | Subaru EZ30 |
| Production | 1999-2009 |
| Cylinder block alloy | Aluminum |
| Configuration | Flat-6 |
| Valvetrain | DOHC 4 valves per cylinder |
| Piston stroke, mm (inch) | 80 (3.15) |
| Cylinder bore, mm (inch) | 89.2 (3.51) |
| Compression ratio | 10.7 |
| Displacement | 2999 cc (183 cu in) |
| Power output (horsepower) | 164 kW (220 HP) at 6,000 rpm 183 kW (245 HP) at 6,600 rpm |
| Torque output | 289 Nm (213 lb·ft) at 4,400 rpm 297 Nm (219 lb·ft) at 4,200 rpm |
| Redline | – |
| HP per liter | 73.3 81.7 |
| Fuel type | Gasoline |
| Weight, kg (lbs) | 180 (397) |
| Fuel consumption, L/100 km (mpg) -City -Highway -Combined |
Subaru Tribeca 13.3 (18) 9.0 (26) 10.2 (23) |
| Turbocharger | Naturally aspirated |
| Oil consumption, L/1000 km (qt. per miles) |
up to 1.0 (1 qt. per 600 miles) |
| Recommended engine oil | 0W-30, 5W-30, 5W-40, 10W-30, 10W-40 |
| Engine Oil Capacity, L (qt.) | With filter change 4.25 l Without filter change 4.0 l |
| Oil change interval, km (miles) | 5,000-10,000 (3,000-6,000) |
| Normal engine operating temperature, °C (F) | 90 (194) |
| Engine lifespan, km (miles) -Official information -Real |
– 300,000+ (180,000) |
| Tuning, HP -Max HP -No life span loss |
300+ – |
M20B25 contains a cylinder block of cast iron. The size of the bore is 84.0 mm (3.31 inches) and the stroke is 75.0 mm (2.95 in). Pistons are combined with two compression rings and a single oil ring.
Aluminum cylinder head #885 produces a great cooling performance. The motor keeps a single overhead camshaft, controlled by the timing belt. It produces an intake and exhaust duration of 256 degrees.
Valves are operated by rocker arms. The width of the intake valves is 42.0 mm (1.65 inches) while the width of the exhaust ones is 36.0 mm (1.42 inches) and the valve lift is 10.1 mm (0.397 inches). Besides, rocker arms serve to control of camshaft follower valve because one of its edges includes an eccentric nut. In addition, they turn around rocker arm shafts.
BMW M20B25 Engine Modifications
1. M20B25 (from 1986 to 1988) is a catalyst engine with a compression index of 9.7. The output is 163 hp at 5,800 rpm and a torque of 215 Nm at 4,000 rpm.
2. M20B25 (from 1985 to 1987) resembles the previous type but without a catalyst. It reaches 171 hp at 5,800 rpm and a torque of 226 Nm at 4,000 rpm.
3. M20B25 (from 1988 to 1991) is a restyled variation with a short intake manifold. The compression rate is 8.8. The capacity is 170 hp at 5,800 rpm and a torque of 222 Nm at 4,300 rpm.
BMW M20B25 Engine Oil Capacity
The BMW M20B25 engine requires 4.5 quarts of 5W-30 oil with a filter replacement.
What Cars Have A BMW M20B25 Engine?
- 1985–1993 E30 325i
- 1989–1990 E34 525i
- 1988–1991 Z1
BMW M20B25 Engine Problems And Reliability
1. Overheating. The cylinder head may overheat owing to the dysfunction of the cooling system. To avoid airlock emergence, it must be checked. Moreover, overheating may be a consequence of a blocked radiator, water pump, or thermostat.
2. Camshaft bed depreciation. After the car runs 125,000-155,000 miles or 200,000-250,000 kilometers, camshaft may start to clatter. The sole solution is to buy a fresh cylinder head.
3. Cylinder head fracture. The cause for that is constantly overheating and usually concerns the 4th or 5th cylinder. By acquiring a fresh cylinder head, the problem will be resolute.
It’s advisable to take care of timing belts and tensioner pulley. Timing belt failure may cause valve deformation. Besides, motor age and the stage of its depreciation may influence steady engine functioning. Honestly, this motor leaves much to be desired. That’s why have a look at some other variants before acquiring them.
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The information provided in this article is for general informational purposes only. The author and publisher make no representations or warranties of any kind, express or implied, regarding the accuracy, adequacy, validity, reliability, availability, or completeness of any information presented. The reader is advised to consult a qualified professional, such as a mechanic or dealership, before making any decisions related to their vehicle's engine oil or maintenance.
