Most Likely Causes:
* Thermostat Stuck Closed: This is the most common culprit. The thermostat regulates coolant flow. If it's stuck closed, the coolant doesn't circulate properly, preventing the engine from warming up. Replacement is relatively inexpensive and easy.
* Low Coolant: Check your coolant level in the overflow reservoir. If it's low, you've got a leak somewhere in the cooling system. This could be a hose, the radiator, the water pump, or even a cracked engine block (less likely). Low coolant will prevent proper heat transfer.
* Faulty Water Pump: The water pump circulates the coolant. If it's failing, coolant won't flow properly, leading to no heat. You'll often hear a whining noise if the water pump is failing.
* Bleeding the Cooling System: Air bubbles trapped in the cooling system can prevent proper heat transfer. The system might need to be bled to remove these air pockets. This is a relatively simple procedure, often outlined in your owner's manual.
Less Likely, but Still Possible Causes:
* Faulty Heater Core: The heater core is a small radiator inside the car that warms the air. If it's clogged, leaking, or otherwise malfunctioning, you won't get heat, even if the engine is getting hot.
* Heater Control Valve: This valve controls coolant flow to the heater core. If it's stuck closed, you'll have no heat.
* Faulty Blower Motor or Resistor: While these don't affect engine heat, a malfunctioning blower motor or resistor will prevent warm air from reaching the cabin, even if the engine is properly heated. You'll likely feel no air movement at all, or only from certain fan speeds.
* Head Gasket Leak: A blown head gasket is a serious issue and can lead to coolant loss and prevent the engine from warming up properly. This is less likely if you're not seeing other symptoms like white smoke from the exhaust, oil in the coolant, or coolant in the oil.
Troubleshooting Steps:
1. Check Coolant Level: This is the first thing you should do. Add coolant if needed, but be careful as the system might be pressurized and hot.
2. Check for Leaks: Visually inspect all hoses, the radiator, and the water pump for any signs of leaks.
3. Feel the Upper and Lower Radiator Hoses: If both hoses are cold when the engine is running, the thermostat is likely stuck closed. If the upper hose is hot and the lower hose is cold, the thermostat might be working, but there could be another problem (like a clogged radiator or water pump issue).
4. Check the Heater Core Hoses: These are usually found behind the dashboard. If they're both cold when the engine is warm, the heater core or heater control valve could be the issue.
5. Try Bleeding the Cooling System: Consult your owner's manual for instructions on how to bleed your specific vehicle's cooling system.
If you're not comfortable working on your vehicle yourself, take it to a qualified mechanic for diagnosis and repair. Ignoring a lack of engine heat can lead to more serious damage.
