Water Pump Impeller Slippage (Plastic Impeller Separation)
SeriousCooling SystemEarly 2.5-litre Duratec V6 engines were fitted from the factory with water pumps featuring a molded plastic (phenolic) coolant impeller. Over thousands of heat cycles, the plastic hub becomes brittle and cracks, losing its press-fit grip on the rotating steel drive shaft. While the external belt pulley spins normally, the internal impeller slips and ceases to circulate coolant effectively at higher engine speeds, leading to sudden, severe cylinder head overheating and potential head gasket failure.
Coolant temperature gauge spikes rapidly towards the red zone when accelerating under load, Heater blowers blow cool air into the cabin despite high engine temperature due to lack of circulation, Coolant boiling and venting past the expansion tank pressure cap into the engine bay
- Check if the water pump has been replaced with a revised unit featuring a metal or brass impeller
- Monitor the temperature gauge on a sustained motorway climb to verify consistent coolant cooling