* Low Coolant Level: The most basic and easiest to check. Open the coolant reservoir (when the engine is cold!) and see if the level is low. If it is, you need to find the leak (see below).
* Water Pump Failure: The water pump circulates coolant through the engine. A failed pump won't circulate coolant, leading to overheating. You'll likely hear unusual noises from the pump if it's failing.
* Thermostat Stuck Closed: The thermostat regulates coolant flow. If it's stuck closed, coolant can't circulate properly, causing overheating.
* Radiator Fan Not Working: The radiator fan helps cool the coolant. If it's not working, the engine will overheat, especially at idle or low speeds. Check the fan fuse and relay.
* Clogged Radiator or Radiator Hoses: Restricted coolant flow due to a clogged radiator or hoses will prevent efficient cooling.
* Head Gasket Leak: A blown head gasket is a serious problem. It can allow coolant to leak into the engine's cylinders or oil, leading to overheating and potentially white smoke from the exhaust. A pressure test is needed to diagnose this.
* Coolant Leak: A leak anywhere in the cooling system (hoses, radiator, water pump, etc.) will cause a loss of coolant and overheating. Look carefully for signs of coolant leakage (greenish or yellowish stains).
* Faulty Coolant Temperature Sensor: While less likely to directly cause the cold air *and* overheating simultaneously, a faulty sensor could give the car's computer incorrect information, leading to improper operation of the cooling system. The cold air could be a secondary effect of the computer trying to compensate for what it thinks is normal temperature.
* Blown Heater Core: A leak in the heater core can result in the loss of coolant, leading to overheating. However, it would more likely cause hot air to be present instead of cold air. A leak causing cold air is less probable but possible if the leak prevents proper pressure in the system.
Why cold air despite overheating?
The cold air is puzzling. Normally, overheating would result in hot air from the heater. The cold air might be a coincidence, a separate issue, or a consequence of:
* Loss of coolant pressure: Low coolant pressure could lead to the heater core not functioning properly.
* Malfunctioning heater control valve: This valve regulates the flow of coolant to the heater core. A malfunction could prevent hot coolant from reaching the heater.
What to do:
1. Check the coolant level: This is the first and easiest step.
2. Inspect hoses and connections for leaks: Look for cracks, bulges, or signs of leakage.
3. Check the radiator fan: Make sure it's working when the engine is running.
4. Have a mechanic check the thermostat, water pump, and head gasket: These require more specialized tools and knowledge to diagnose.
Do not attempt to open the radiator cap or any other high-pressure component of the cooling system while the engine is hot or even warm. The pressurized, super-hot coolant can cause severe burns. If you're not comfortable working on your car yourself, take it to a qualified mechanic for diagnosis and repair.
