BMW 2.5si
Lightweight six-cylinder with magnesium crankcase and Valvetronic. Very smooth; oil filter housing gasket and VANOS solenoids are typical wear items.
Facelift Pick: Light and Eager
218 hp from the modern N52 — deep rumble down low, brilliant above 5,000 rpm. More motor, same Z4 charm, more reliable than the M54. The sweet spot in the Z4 range.
Engine Weaknesses 7
The N52 electric water pump is a known wear item. When it fails the engine overheats quickly. Recommended: preventive replacement when any abnormalities appear or from around 100,000 km.
Symptoms: Coolant temperature gauge rises quickly, coolant loss, audible pump malfunction, engine overheating.
The eccentric shaft sensor on the N52B25 Valvetronic system fails sporadically. Fuel consumption jumps sharply by 30–35%; the sensor costs approximately €315 new from BMW.
Symptoms: Sporadic eccentric shaft sensor fault code; fuel consumption jumps from ~10 to ~13.5 L/100 km; power loss; whistling noise under acceleration
The seals in the oil-coolant heat exchanger inside the oil filter housing become porous and allow oil into the coolant. Affects N52, N53, and N54 equally. Always replace both seals at the same time.
Symptoms: Oil film on the coolant surface; oily-looking oil filler cap; no white smoke or visible fluid loss despite apparent head gasket symptoms
The magnesium alloy cam cover develops hairline cracks from thermal cycling — preferentially at cylinders 5 and 6. Small cracks cause oil leaks resembling a gasket leak.
Symptoms: Oil leak at the rear of the engine, oil smell inside the cabin, crack often only visible after cleaning the engine bay.
The VANOS camshaft adjustment solenoid valves become fouled or wear — fault codes P0011/P0015 (intake/exhaust camshaft), metallic grinding above 2,500 rpm under load.
Symptoms: Rough idle, power loss at low revs, fault code P0012 or P0015, grinding from the cam cover area under load.
The N52 magnesium cam cover has known sealing problems. Oil loss at the cam cover gasket, eccentric shaft sensor, and camshaft adjustment motor are common. Aluminium bolts must not be reused.
Symptoms: Oil loss at the cylinder head, oil smell, visible oil traces at the top of the engine, oil spots on the exhaust manifold.
The CCV is integrated into the cam cover and replaced together with it. A defective membrane valve causes crankcase overpressure and contaminates the throttle body and intake tract.
Symptoms: Rough idle, rpm fluctuations, oil mist on the throttle body, overpressure escapes when opening the oil filler cap on a running engine.
Vehicle Weaknesses 7
The hydraulic pump for the Z4 E85 hood is mounted in a poorly protected position. Blocked drains allow water ingress; the pump corrodes and fails. Replacement is labour-intensive and expensive.
The electric power steering on the Z4 E85 occasionally fails — particularly on short-trip drivers as the battery becomes too weak. Steering angle sensor faults and column defects also occur.
The N46B20 four-cylinder in the 2.0i Z4 E85 suffers from premature timing chain wear due to a weak chain tensioner. Neglected oil maintenance causes the chain to elongate and can lead to engine damage.
Water enters through leaking tail lights or the boot vent. The expansion rivets on the tail lights become porous, seals age and allow moisture in. Can lead to short circuits and mould.
Ignition coil failures are a known issue on the Z4 E85, particularly at higher mileage. Oil from the valve cover gasket into the spark plug tubes is often a contributing factor. Multiple coils can fail in succession.
The sporty suspension setup on the Z4 E85 leads to above-average tyre wear, especially at the rear. Rear tyres can be at the wear limit after just 25,000 km. Broken springs have also been reported.
On the E85 Z4, the rain sensor and window regulator motors fail more often than usual. The rain sensor triggers in sunshine; windows move jerkily or not at all — both are age-related symptoms.
Reports & Tests
1161 owner complaints filed with NHTSA (2002–2008). Most reported: Steering (965), Airbags (86), Electrical (52).