* Head gasket failure: This is a major problem. A blown head gasket allows coolant to leak into the cylinders or oil, or vice-versa, causing overheating and often leading to white smoke from the exhaust, milky oil, or loss of coolant without visible leaks.
* Cracked engine block or cylinder head: Similar to a head gasket failure, a crack in the engine block or cylinder head allows coolant to escape and the engine to overheat. This is often catastrophic and requires extensive repairs.
* Water pump failure: While a failing water pump is a common cause of overheating, it's sometimes missed. A water pump that's failing might still move *some* coolant, preventing immediate catastrophic failure, but insufficient circulation will lead to overheating, especially under load.
* Clogged heater core: A severely restricted heater core can restrict coolant flow, leading to overheating. This is less common as a primary cause of overheating but can contribute if other issues are also present.
* Faulty radiator cap: A faulty radiator cap can't maintain the proper pressure in the cooling system, leading to boiling and overheating.
* Problems with the cooling fan(s): The cooling fan might not be turning on at the right time, or at all, due to a faulty fan relay, sensor, or the fan motor itself.
* Air in the cooling system: Air pockets can prevent efficient coolant flow and cause localized overheating. This is sometimes caused by improper bleeding of the system after maintenance.
* Thermostat stuck open (rare but possible): While a stuck *closed* thermostat is much more common, a stuck *open* thermostat can cause overheating if the coolant flow isn't sufficient to handle the heat load under strenuous conditions.
* Low compression in one or more cylinders: Low compression leads to increased heat generation in that cylinder, which can contribute to overheating the whole engine. This is usually accompanied by other symptoms, like loss of power.
It's important to note that these are *in addition* to the typical overheating causes. If your car is overheating and you've checked the obvious things (coolant level, thermostat, radiator), it's crucial to take it to a qualified mechanic for diagnosis before further damage occurs. Driving a car with an overheating engine can cause severe and costly engine damage.
