BMW 323i

The plastic impeller of the M52B25 water pump can slip on the shaft at high mileage. The pump appears to spin normally but no longer circulates coolant. Overheating with cylinder head damage follows quickly.

Symptoms: Coolant temperature rises suddenly on motorway runs, heater output drops, overtemperature warning

Early M52B25 with Nikasil-coated cylinder bores are affected by premature corrosion with sulphur-rich fuel. The coating is attacked and oil consumption rises sharply.

Symptoms: Massively increased oil consumption (>1 litre/1,000 km), blue smoke from the exhaust, measurable compression loss

The DISA variable intake valve breaks at the shaft base or the membrane tears. Fragments can be sucked into the engine and cause catastrophic damage.

Symptoms: Power loss in the lower rev range, rattling or clattering from the intake area, in the worst case engine damage from ingested fragments.

The Behr/Mahle electric coolant thermostat fails prematurely. Failure causes overheating or permanent cold running with increased fuel consumption.

Symptoms: Engine does not reach operating temperature or overheats, poor heater output, increased fuel consumption.

The plastic expansion tank of the M52B25 develops hairline cracks with increasing years of service, which open under heat. Coolant loss can be gradual or sudden.

Symptoms: Coolant level drops regularly, visible cracks on expansion tank, coolant puddle under the car after parking

The O-rings in the M52B25 single-VANOS harden and lose their sealing effect. Oil pressure loss in the VANOS system degrades camshaft adjustment performance.

Symptoms: Judder during warm-up, power loss on a cold engine, irregular idle speed when coolant temperature is below 60°C

The cast rear trailing arms (swing arms) of the E36 rear axle are prone to corrosion and pitting near the spring seat. When severely affected the trailing arm must be replaced.

The viscous fan coupling loses its silicone oil over time and can no longer couple the engine fan adequately. In traffic or at low speeds, engine temperature rises rapidly into the red zone.

The rubber-metal barrel bearings (Tonnenlager) of the rear axle become porous and separate. Repair requires special tools and full rear axle disassembly. MOT-relevant when heavily worn.

Sills rust through almost universally — especially through blocked drain holes. Wheel arches rust from the inside along the flange joint, only visible once damage is already severe.

Water pump and thermostat are wear items. A faulty thermostat causes permanent under- or overheating; a failed water pump leads to coolant loss and engine damage.

The alternator voltage regulator and the EWS electronic immobiliser are classic weak points. The voltage regulator fails most often, rarely the whole unit. EWS can cause intermittent start failures.