Plastic cooling-system parts (M52TU / M54)

Engine / equipment

M52TU and M54 six-cylinder petrol (320i–330i E46, 520i–530i E39, 520i–530i E60 up to 2005, X3 2.5i/3.0i, X5 3.0i, six-cylinder Z3 and Z4)

Period mentioned

1998–2006

Symptoms

Coolant loss without an obvious puddle, sweet smell, low-level warning, steam in the engine bay, heater stops warming and the temperature needle rises. Expansion tank failure is usually sudden; the water pump can fail with no visible leak.

Possible cause described

Many cooling parts are plastic and become brittle with heat and age: expansion tank, radiator neck, thermostat housing and the water pump impeller, which can crack or come off its shaft and stop pumping. The electric auxiliary pump is also a frequent failure.

Check for the garage

With the engine cold, check the level and look for cracks or dried coolant on the tank, radiator neck and thermostat housing. At a garage: pressure-test the system and inspect the pump. If the temperature rises, stop somewhere safe: a single overheat can warp the aluminium head. Never open the system hot.

Cost cited in the source

No verifiable estimate in the sources; ask for a quote. The sources recommend replacing tank, pump (preferably with a metal impeller), thermostat and hoses together on high-mileage engines.A rough figure from the original database, not an up-to-date quote.

Sources from the original database