Coolant pump failure
Major $900–$2,000All 991, more commonly on higher-mileage cars.
The coolant pump fails, sometimes shedding impeller material into the cooling system. Caught early it is a routine part; caught late it means flushing debris out of the whole system.
- Coolant temperature climbing in traffic
- Coolant weeping at the pump
- Coolant loss with no obvious external leak
- Overheat warning under sustained load
Replace with the thermostat while the system is open. Many owners treat it as a preventive item at high mileage rather than waiting for it.