1. Fan Motor Issues:
* Burned-out motor: The most straightforward reason. The fan motor itself might have failed due to age, overheating, or a short circuit. Testing the motor with a multimeter (to check for power and continuity) is crucial.
* Bad fan switch/relay: The fan might not be receiving the signal to turn on. This could be a faulty relay (a small electrical switch) that controls the fan or a problem with the temperature switch in the radiator or thermostat housing that sends the signal to activate the relay.
* Wiring problems: Broken, corroded, or loose wires in the fan circuit can prevent power from reaching the motor. A thorough visual inspection of all wiring is necessary.
* Fuse blown: A blown fuse in the fan circuit will also prevent the fan from operating. Check the fuse box for a blown fuse related to the cooling fans.
2. Fan Clutch Issues (if applicable):
The '85 DeVille *might* have a viscous fan clutch (though some models used electric fans only). If it has a clutch:
* Clutch failure: The clutch might be seized or worn out, preventing the fan from spinning at the proper speed. A seized clutch will feel stiff when you try to turn the fan blades manually.
3. Thermostat Issues:
* Stuck closed thermostat: If the thermostat is stuck closed, coolant won't circulate properly through the radiator, leading to overheating and potentially not triggering the fan.
4. Coolant Level and Condition:
* Low coolant: Insufficient coolant reduces the system's cooling capacity.
* Contaminated coolant: Rust, scale, or other contaminants can impede heat transfer.
5. Radiator Issues:
* Clogged radiator: A radiator clogged with debris reduces its cooling efficiency.
* Radiator leaks: Leaks prevent proper coolant flow.
6. Water Pump Issues:
* Failed water pump: A malfunctioning water pump doesn't circulate coolant effectively, leading to overheating and a greater demand on the cooling fans.
Troubleshooting Steps:
1. Check coolant level: Add coolant if low (ensure engine is cool before opening the radiator cap).
2. Check for leaks: Look for visible leaks around hoses, radiator, water pump, etc.
3. Check fuses: Inspect the fuse box for any blown fuses related to the cooling fans.
4. Check fan operation: With the engine running and warmed up, observe whether the fan turns on. If not, use a multimeter to test the fan motor, wiring, relay, and temperature switch.
5. Inspect the radiator: Look for clogs or damage.
6. Check the thermostat: Ensure it opens when the engine reaches its operating temperature.
7. Inspect the water pump: Listen for unusual noises; a failing water pump often makes a whining or gurgling sound.
If you're not comfortable working on your car's electrical system or cooling system, it's best to take it to a qualified mechanic for diagnosis and repair. Improperly addressing these issues can lead to severe engine damage.
