* Faulty Thermostat: The thermostat controls coolant flow. If it's stuck open, coolant constantly circulates without reaching a high enough temperature to properly heat the cabin. This is the most likely culprit.
* Low Coolant Level: Insufficient coolant means less heat transfer, leading to cold air even if the engine isn't overheating. Check your coolant reservoir.
* Coolant Leak: A slow leak can deplete coolant over time, resulting in reduced heating capacity. Look for any signs of leaks around hoses, the radiator, or the engine block.
* Worn Water Pump: A weak or failing water pump might not circulate coolant effectively, even if the thermostat is working correctly.
* Bleeding the Cooling System: Air pockets in the cooling system can hinder proper coolant circulation and heating. The system might need to be bled.
* Faulty Heater Core or Hose: A problem within the heater core itself (the radiator inside the car) or its associated hoses could restrict hot coolant from reaching the vents.
* Faulty Heater Blower Motor Resistor: While this wouldn't directly affect coolant temperature, a malfunctioning resistor could cause the fan to run at low speed, making the already-cool air seem even colder. This is less likely given you mention "cold air from the engine."
What to do:
1. Check the coolant level: This is the easiest first step. Top it up if low (using the correct type of coolant for your Fiesta), but be cautious of adding coolant to a hot engine.
2. Inspect for leaks: Look carefully around all components of the cooling system for any signs of leaks.
3. Feel the radiator hoses: When the engine is running, feel the upper and lower radiator hoses. The upper hose should be hot; if both are cool, the thermostat might be stuck open.
4. Consult a mechanic: If you're not comfortable inspecting the cooling system yourself, take your car to a trusted mechanic. They have the tools and expertise to diagnose the problem accurately.
Ignoring this could lead to more serious issues later, especially if there is a leak or a faulty water pump. Don't drive long distances with a potentially faulty cooling system.
