Bulletin
Engine code

IA Technical Bulletin

BMW M50 Engine Guide

Engine: M50

Bulletin text

The M50 is BMW's inline-6 for the E34 5 Series and E36 3 Series, a chain-driven engine that replaced the belt-driven M20. Wikipedia lists the original M50 for 1990-1992 and the M50TU, the first BMW engine with variable valve timing (a single VANOS on the intake camshaft), for 1992-1996. BMW service information supports the split: a BMW bulletin refers to the M50B25 'without VANOS' built from 5/89 to 8/92, and BMW repair documents treat the M50 and the M50 with VANOS as separate variants.

BMW sold the M50 in US-market cars. The M50 is a separate engine from the M52 that followed it and from the S50 used in the M3, which are not covered here.

Quick read

Ownership position: Not established yet. We are still researching this engine.
Reliability: Not established yet. BMW's recalls and service bulletins below cover specific, dated items; none of them is an engine-wide rating.
Cost to own: Not established yet. We are still researching this engine.
Power potential: Not established yet. No BMW document we opened gives a tuning limit; factory output is in Technical Specifications.
Main watch item: The idle control valve on the M50 built from 5/89 (BMW service bulletin 13 01 96).

M50 At a Glance

Question	Practical answer
Sold in US-market BMWs?	Yes. BMW's US-specification parts data lists the M50 in the cars under Where you find it.
Generations	Original M50 without VANOS and the M50TU with VANOS.
Factory output	Wikipedia lists the M50B25 at 141 kW (192 PS) at 6,000 rpm and 245 Nm at 4,700 rpm, and the M50B25TU at 141 kW at 5,900 rpm and 250 Nm at 4,200 rpm.
Block	Wikipedia lists a cast iron block with an aluminum head. BMW's cylinder head bolt table puts the M50 in the same tightening group as the M52 with a cast iron engine block.
Engine oil	BMW's February 2017 oil chart (SI B11 01 15) lists 5W-30 LL01 or 0W-30 LL01FE for all BMW gasoline engines of model year 2011 and older.
Oil capacity	BMW's fluid data lists 6.5 liters for the US E36 320i and 325i and 5.75 liters for the US E34 525i.
Oil consumption allowance	BMW's SI B11 03 13 says all BMW engines except Motorsport engines can use up to 1 quart of oil per 750 miles at any time.
Recalls tied to M50 cars	NHTSA lists a 1998 cooling system recall (98V-178) and a 1997 throttle and cruise control cable recall (97V-131) that include the 325i, 325is and 525i of the M50 years; neither is specific to the M50.
Reliability profile	Not established yet. We are still researching this engine.
Typical annual planning budget	Not established yet. We are still researching this engine.
Common tuned street range	Not established yet. We are still researching this engine.
Before buying	Confirm whether the car has the original M50 or the M50TU with VANOS, then ask a BMW dealer to check your VIN for open recalls.

Where you find it

BMW's US-specification parts data lists the M50 in the chassis below. The parts data ends in December 2019 and shows catalog build dates, which can start before US sales.

Chassis	US model, body and build dates (BMW parts catalog)
E34	525i sedan, built 6/1990-12/1995
E34	525i wagon, built 10/1991-1/1996
E36	320i sedan, built 10/1992-5/1995
E36	325i convertible, built 12/1992-9/1995
E36	325i sedan, built 10/1990-10/1995
E36	325is coupe, built 1/1991-9/1995

BMW's service bulletin 13 01 96 gives the M50 production start as 5/89, while Wikipedia dates the original M50 to 1990 and the parts catalog starts its US entries in 6/1990.

Technical Specifications

Specification	Detail
Configuration	Wikipedia lists a dual overhead camshaft layout with four valves per cylinder, chain-driven.
Displacement and bore x stroke	Wikipedia lists the M50B25 at 2,494 cc (84 x 75 mm) and the M50B20 at 1,991 cc (80 x 66 mm).
Compression ratio	Wikipedia lists 10.0:1 for the M50B25 and 10.5:1 for the M50B25TU.
Valvetrain	Wikipedia says the M50TU adds a single VANOS system on the intake camshaft that works as an on/off system.
Engine management	Wikipedia lists Bosch Motronic 3.1 on the M50 and 3.3 on the M50TU.
Block and head	Wikipedia lists a cast iron block and an aluminum alloy head. BMW's cylinder head bolt table groups the M50 with the M52 with a cast iron engine block.
Timing drive	BMW's parts catalog lists a timing chain (11 31 1 432 176) for the M50.
Engine oil	5W-30 LL01 or 0W-30 LL01FE (BMW February 2017 oil chart, model year 2011 and older).
Oil capacity	See At a Glance.
Firing order	Not established yet. We are still researching this engine.

Factory Deep Dive

Original M50 and M50TU

BMW's idle control valve bulletin splits the early M50: M50B20 built from 5/89, and M50B25 without VANOS built 5/89 to 8/92. Wikipedia gives the M50TU introduction as September 1992.

Wikipedia says the M50TU head is recognizable by a distinctive bump on one side.

Iron block

Wikipedia calls the M50TU the last non-M BMW engine with a cast iron block for worldwide use. BMW's cylinder head bolt table puts the M50 in the same tightening group as the M52 with a cast iron engine block; we did not find a BMW document that states the M50 block material directly.

Idle air control

BMW's bulletin says dirt can make the early M50 idle speed control valve (types EWD1 and ZWD2) stick at times. It rules out the later EWD3.2 and ZWD5 types as the cause, even when they show black deposits.

Service Parts at a Glance

Part	BMW part number (current)	Note
Spark plug, High Power	12 12 0 037 607	Current; BMW's replacement for 12 12 9 071 003; listed for M50, M52, M54 and M56 cars.
Spark plug	12 12 9 064 617	Current; listed for M50 cars built to 1/1993 and M52 cars.
Spark plug (later M50)	12 12 9 063 428	Current; listed for M50 cars built from 1/1993.
Ignition coil	12 13 7 599 218	Current; listed for US E36 M50 cars (320i, 325i, 325is) built 10/1990-10/1995; not listed for the E34 525i.
Coolant pump (mechanical)	11 51 7 527 799	Current; listed for M50 and M52 cars.
Thermostat	11 53 7 511 083	Current; listed for M50 and M52 cars.
Cylinder head cover (to 9/1992)	11 12 1 738 171	Current; listed for M50 cars built to 9/1992.
Cylinder head cover (from 9/1992)	11 12 1 738 410	Current; listed for M50 cars built from 9/1992.
Timing chain	11 31 1 432 176	Current; also listed for M52, M54 and M56 cars.
Air filter element	13 72 1 730 449	Current; listed for US E36 M50 cars, not the E34 525i; also listed for M52, M54 and M56 cars.

A matching part number locates a part; it does not confirm that it fits a specific VIN.

Known Failure Points and Service Items

Recall information on this page was checked against NHTSA on October 1, 2026. Recalls are added and closed over time. Whether a specific car is covered is a VIN check with BMW or NHTSA.

01 Idle control valve soiling (service bulletin 13 01 96)

BMW's bulletin covers the M50B20 built from 5/89 and the M50B25 without VANOS built 5/89 to 8/92. It describes idle speed that stays at 1000-1200 rpm after starting, stalling when a load such as the A/C compressor cuts in, and idle speed that dips or hunts, caused by a soiled idle speed control valve; BMW's fix is an optimized valve and a modified air hose with a dirt trap.

Watch for a high or hunting idle after a cold start and stalls when the A/C or steering is loaded on a car in that window.

02 Long cold starts, US models (service bulletin 12 01 97)

BMW's bulletin covers US E34 and E36 cars with the M50, with and without VANOS, built from September 1990 to January 1996. It describes long cranking when cold-starting at ambient temperatures of about -3 to +7 degrees C, sometimes with dark exhaust smoke and damp spark plugs, attributed to fuel with too many low-boiling components, and BMW's fix is an engine control software update.

Watch for long cranking on cool mornings, dark exhaust smoke on a cold start and damp spark plugs.

03 Valve train rattle after a cold start (service bulletin 11 10 98)

BMW's bulletin 11 10 98 covers the M50 and other engines with hydraulic valve clearance elements and says rattling right after a cold start is traced to the higher viscosity of cold oil. BMW says these noises do not shorten engine life.

Watch for rattling that stays after the engine is warm or follows a very low oil level.

04 Cooling system recall (98V-178)

NHTSA lists recall 98V-178 (August 1998, 340,000 vehicles) for 1988-1995 BMW models including the 325i, 325is and 525i. NHTSA's record says a failure of a coolant system component such as the thermostat, water pump or fan belt can raise coolant temperature and pressure, and that a crack or separated seam in the heater core end piece could expel hot coolant and injure an occupant. The remedy is a new-design radiator cap.

Watch for a temperature warning, coolant loss or a cap that no longer holds pressure.

05 Throttle and cruise control cables (97V-131)

NHTSA lists recall 97V-131 (August 1997, 410,000 vehicles) for BMW models including the 1992-1995 325i and 325is and the 1989-1995 525i. NHTSA's record says a plastic bushing on the throttle or cruise control cable can break, the cable housing can separate, and the throttle valve could stay partly open so the car may not slow as expected. The remedy is a spring steel clip on the outer tube of each cable.

Watch for a throttle that hangs open or a car that does not slow when the pedal is released.

06 Oil consumption and crankcase ventilation

BMW's oil consumption bulletin SI B11 03 13 says all BMW engines except Motorsport engines can use up to 1 quart of oil per 750 miles at any time. It lists maintenance, external leaks, overfilling, oil viscosity, engine speed and load, and a malfunctioning crankcase ventilation system among the causes to check before engine repairs.

Watch for oil use beyond that allowance, with an engine that is otherwise leak-free and correctly filled.

Reliability Verdict

Not established yet. We are still researching this engine. The bulletins and recalls above are narrow, dated items and none of them rates the M50 as a whole.

Power Potential

Not established yet. We are still researching this engine. No BMW document we opened gives a tuning limit for the M50.

Cost of Ownership

Not established yet. We are still researching this engine. No BMW document gives repair costs or a service reserve.

Common Questions

What BMW has the M50 engine?

BMW's US-specification parts data lists the M50 in the E34 525i sedan and wagon and the E36 320i, 325i sedan, 325i convertible and 325is coupe.

What is the difference between the M50 and the M50TU?

Wikipedia says the M50TU, introduced in September 1992, added a single on/off VANOS system on the intake camshaft, and BMW's service information treats the M50 and the M50 with VANOS as separate variants.

Does the M50 have an iron block?

Wikipedia says both the M50 and M50TU have a cast iron block with an aluminum head, and BMW's cylinder head bolt table puts the M50 in the same tightening group as the M52 with a cast iron engine block.