* Low coolant: This is the most basic and important check. Low coolant means the system can't effectively absorb and dissipate heat. Check the coolant level in the radiator's overflow reservoir (when cold) and look for leaks.
* Radiator issues: A clogged radiator restricts coolant flow, reducing its ability to cool the engine. A damaged radiator (leaks, holes) will also cause overheating.
* Water pump failure: The water pump circulates coolant. A failing pump won't circulate coolant effectively, leading to overheating, especially under load (like the AC compressor).
* Thermostat stuck closed: The thermostat regulates coolant flow. If it's stuck closed, coolant won't circulate properly until the engine reaches a dangerously high temperature.
* Cooling fan issues: The cooling fan helps dissipate heat, especially at idle when the car's speed isn't providing airflow. A non-functioning fan, a fan clutch that doesn't engage, or a faulty fan relay will all cause overheating while idling, especially with the AC on (which adds heat load).
* AC condenser issues: The AC condenser is located in front of the radiator. If it's clogged with debris or damaged, it reduces airflow through the radiator, hindering cooling.
* Head gasket failure: While less likely as a primary cause of *only* idling overheating with AC on, a failing head gasket can allow combustion gases to leak into the cooling system, causing pressure buildup and overheating. This would usually be accompanied by other symptoms like white exhaust smoke, milky oil, or loss of coolant without visible leaks.
Why idling with AC makes it worse:
The AC compressor adds significant load to the engine. This increases the engine's heat production. At idle, the engine speed is low and the airflow through the radiator (from the vehicle's speed) is minimal. This combination makes it much harder for the cooling system to manage the extra heat generated by the AC.
Troubleshooting steps:
1. Check coolant level: This is the first and easiest check.
2. Check for leaks: Carefully inspect all hoses, the radiator, and the water pump for leaks.
3. Inspect the cooling fan: Ensure it turns on when the engine gets warm, both at idle and with the AC on. Listen for it.
4. Check the radiator: Look for clogs or damage.
5. Consider a thermostat replacement: Relatively inexpensive and common cause of overheating.
If you're not comfortable performing these checks yourself, it's best to take the Caravan to a mechanic for diagnosis and repair. Ignoring overheating can lead to serious engine damage.
