A stuck-open engine cooling system thermostat could cause all of the symptoms.
- Poor heater operation
- Below-normal engine operating temperature
- Increased fuel consumption: A stuck-open thermostat would cause increased fuel consumption because the engine would take longer to build engine temperature and could not sustain normal operating temperature; especially in colder climates.
Can a car overheat if the thermostat is stuck open?
Engine overheating: A stuck-open thermostat would not cause overheating. An open thermostat would be the normal position for a warmed-up engine. The engine thermostat speeds engine warm-up by restricting coolant flow until a predetermined temperature is reached. Poor heater operation and excess fuel consumption would be caused by slow warm-up. The thermostat also serves to regulate coolant flow, which keeps the engine at an acceptable and efficient operating temperature.