* Increased Load: The air conditioner puts an extra load on the engine. A slightly weakened cooling system, perhaps due to low coolant, a failing water pump, or a partially clogged radiator, might only show its weakness under this added stress. Overheating *could* be caused by these issues, which are less serious than a blown head gasket.
* Head Gasket's Role: A blown head gasket can allow coolant to leak into the cylinders, reducing cooling efficiency and potentially leading to overheating, especially under load (like when the AC is on). However, a head gasket failure often presents with other symptoms, such as white smoke from the exhaust, milky oil, or loss of coolant without visible leaks.
In short: Overheating with the AC on is a red flag that warrants investigation, but it's not diagnostic of a blown head gasket. You need to have a mechanic diagnose the cause. They will likely check:
* Coolant level: Is it low?
* Radiator and hoses: Are they clogged, leaking, or damaged?
* Water pump: Is it functioning correctly?
* Thermostat: Is it opening and closing properly?
* Coolant pressure: Is there excessive pressure in the system?
* Exhaust for signs of coolant: White smoke indicates combustion of coolant.
* Oil for signs of coolant: Milky or frothy oil suggests coolant mixing with oil.
* Compression test: To check for leaks between cylinders and the cooling system (indicative of a head gasket failure).
Don't ignore overheating. Continue driving with an overheating engine can cause significant and costly engine damage. Get it checked out promptly.
