* Low coolant level: This is the simplest and most common cause. The AC compressor puts extra strain on the engine, requiring more efficient cooling. If your coolant level is low, the system can't dissipate the heat effectively, leading to overheating. Check your coolant reservoir and top it off if needed (ensure the engine is cool before doing so!). A low coolant level might indicate a leak somewhere in the system.
* Faulty water pump: The water pump circulates coolant through the engine. A failing water pump might not circulate coolant effectively, especially under the increased load of the AC. This leads to localized overheating.
* Clogged radiator: A clogged radiator restricts coolant flow, reducing its ability to cool the engine. Dirt, debris, and corrosion can all contribute to clogging.
* Failing thermostat: The thermostat regulates coolant flow. A stuck-closed thermostat prevents coolant from circulating, causing overheating. A stuck-open thermostat can also contribute, though less directly, by reducing the engine's ability to reach optimal operating temperature quickly.
* Malfunctioning radiator fan: The radiator fan helps cool the radiator. If the fan isn't working properly (or the fan clutch is bad), the radiator won't be cooled effectively, especially when the engine is working harder with the AC on. This is a very common cause.
* AC compressor issues (indirectly): While not directly causing overheating, a poorly functioning AC compressor can draw excessive power, causing the engine to work harder and generate more heat. This extra heat can overwhelm a cooling system that is already on the verge of failure. A failing compressor isn't usually the primary cause of overheating, but can exacerbate an existing issue.
* Leaking head gasket: A blown or leaking head gasket can allow coolant to leak into the cylinders or oil, leading to overheating and potentially other serious engine problems. This is a more serious and costly problem.
Important Note: Overheating can cause significant engine damage. If your PT Cruiser is overheating, do *not* continue driving it. Pull over to a safe location, turn off the engine, and let it cool down before attempting to diagnose the problem. It's best to have a qualified mechanic inspect the vehicle to determine the exact cause and perform necessary repairs.
