M50 BMW — E36/E34 platform Petrol 1990-1996

M50 engine — BMW 2.5 (2.5L I6 24V DOHC)

2.5L I6 24V DOHC · 150-192 hp · 245-245 Nm

The M50 is BMW's six-cylinder petrol with twin overhead cams and 24 valves, built 1990-1996 as the 2-litre M50B20 and the 2.5-litre M50B25 with 150-192 hp. It is found in the E36 320i and 325i and the E34 520i and 525i; the later M50TU added single VANOS. Typical visits are hardened VANOS solenoid O-rings on TU engines, brittle plastic cooling parts, valve cover gasket and spark plug tube seal leaks, a carbon-fouled idle control valve, crankshaft position sensor failures causing hot no-starts, and leaking lower intake manifold gaskets, front crank seals and injector O-rings. The duplex timing chain is robust, though the plastic guides can crack at high mileage. Torque figures cover the head bolts, crank pulley, camshaft sprockets, VANOS central bolt, main bearing caps and connecting rod bolts.

For a hot no-start or random stall, check the crankshaft position sensor connector at the bellhousing first and back-probe for a signal while cranking. Low-end torque loss with rough idle on a TU engine points to the VANOS seals. Burning oil smells usually come from the valve cover gasket, plug tube seals or lower intake gaskets, and the cooling system should be pressure-tested before the car leaves.

Check first

Crankshaft position sensor connector for internal corrosion.
VANOS solenoid and piston seals on TU engines with P1519/P1523.
Valve cover gasket and spark plug tube seals together.
Rear coolant pipe connections under pressure for hidden leaks.
Sump and pickup screen for guide debris during any chain job.
Idle control valve for carbon on hunting idle.

Values cited from a licensed workshop database. On the M50, the head bolts: 30 Nm + 90° + 90° (TTY, new bolts).

Engine overview

Manufacturer

BMW — E36/E34 platform

Displacement

2.5 L

Configuration

I6 24V DOHC

Power

150-192 hp

Torque

245-245 Nm

Production years

1990-1996

Fuel type

Petrol

Vehicles with this engine

BMW E36 320i (M50B20) BMW E36 325i (M50B25) BMW E34 520i (M50B20) BMW E34 525i (M50B25)

Known failures & weak points

M50B25TU single-VANOS: solenoid O-rings harden and crack around 120,000–180,000 km, causing loss of low-end torque, rough idle, and VANOS-related fault codes (P1519/P1523). Repair is a reseal of the VANOS unit's solenoid and piston seals.

Plastic cooling-system parts (thermostat housing, expansion tank, radiator end-tanks) become brittle with age on E34/E36 M50 cars and can crack, causing coolant loss and overheating risk. This is a general weakness of BMWs of this era, not unique to the M50.

Lower intake manifold gaskets can weep oil onto the block over time, causing a burning-oil smell; inspect and replace as a set during valve cover service.

The crankshaft position sensor, mounted near the bellhousing, can fail intermittently from heat soak and connector corrosion, causing a hot no-start or random stalling with no spark/injection pulse.

Oil leak from camshaft cover (valve cover) gasket at 60,000–100,000 km: rubber gasket hardens and shrinks, leaking oil onto exhaust manifold. Root cause is prolonged heat exposure. Symptoms: burning oil smell, visible oil on exhaust, potential smoke. Also inspect spark plug tube seals simultaneously as they fail at same interval.

Idle control valve (ICV) carbon fouling at 80,000–120,000 km: Bosch rotary ICV accumulates carbon deposits from crankcase ventilation gases, causing rough idle, hunting idle, and stalling at warm-up. Root cause is PCV system routing blow-by through the ICV.

The front crankshaft seal can wear and leak, contaminating the serpentine belt and dripping onto the subframe; avoid hammering the harmonic balancer off, as it can damage the pulley hub or seal surface.

Fuel injector O-ring degradation at 100,000–150,000 km: lower injector O-rings harden and crack, causing fuel smell in intake manifold, rough running, and lean misfires. Root cause is Buna-N O-rings degrading from ethanol-blended fuels (E10). Symptoms: fuel odor from engine bay, P030X misfire codes, rough idle. Consider ultrasonic injector cleaning at same interval.

Common torque specifications

Head Bolts	30 Nm + 90° + 90° (TTY, new bolts)
Crank Pulley Bolt	410 Nm — NOT TTY, reusable. Requires flywheel locking tool (BMW 11-2-160) to prevent rotation. Impact gun acceptable for removal only; torque wrench mandatory for installation. unconfirmed
Camshaft Sprocket Bolts	20 Nm — apply Loctite 243 (medium strength) to threads; do not over-torque or strip aluminum cam nose unconfirmed
VANOS Central Bolt (M50TU)	60 Nm — requires camshaft holding tool (BMW 11-3-240); verify VANOS timing marks aligned before final torque unconfirmed
Main Bearing Cap Bolts	Stage 1: 20 Nm; Stage 2: +70° angle — TTY, replace on reassembly unconfirmed
Connecting Rod Bolts	Stage 1: 20 Nm; Stage 2: +70° angle — TTY, replace on reassembly unconfirmed
Connecting Rod Cap Bolts	20 Nm + 70° (TTY, new bolts)

Figures marked unconfirmed could not be cross-checked against a workshop source. Verify against the vehicle’s own documentation before tightening.

Service intervals

Timing Chain	Duplex chain — inspect at 150,000 km; no mandatory replacement interval but replace if slack exceeds 3 links of travel on tensioner or cold-start rattle persists beyond 3 seconds
Oil Change Km	10000
Oil Spec	5W-30 ACEA A3/B4 (BMW Longlife-98 compliant) — OEM BMW Twin Power Turbo or Castrol Edge 5W-30 LL
Oil Capacity L	6.5
Coolant Spec	BMW HT12 (blue) ethylene glycol, 50/50 premix — do NOT use OAT or universal green coolant; silicate-free formula required

Pro tips from the field

Distinguish M50 from M50TU by the presence of the VANOS unit and solenoid at the front of the cylinder head — non-TU M50 (pre-1992) has no VANOS hardware, while M50TU does.

When diagnosing a no-start or intermittent stall, always check the crankshaft position sensor connector FIRST before condemning the DME. The 2-pin connector at the bellhousing corrodes internally while appearing clean externally. Backprobe with a multimeter for 0–5V square wave signal during cranking — no signal with good connector tension means sensor replacement.

The M50 timing chain is robust, but the plastic guide rails can crack and shed fragments into the oil pan at high mileage. When doing a chain job, always drop the pan to check for debris and clean the oil pump pickup screen if any is found.

On coolant system rebuilds, pressure-test the system before returning the car — small leaks at rear coolant pipe connections can be invisible without pressurizing the system.

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Who makes these pages, and how

TorqFix was built by a mechanic — after a 2,700 km drive with five roadside repairs that no diagnostic tool could explain.

The figures on this page come from manufacturer workshop documentation and are shown as they are. The page is assembled automatically from that data — it is not written by an AI. The AI works in the chat, where it answers for your specific car. It writes nothing here.

Variants of the same model differ. Cross-check torque against the factory manual for your engine before final tightening.

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Workshop data on this page last updated 22 Aug 2026.