Cooling fan failure is the primary culprit causing engine overheating. Mastering self-checking skills can prevent significant losses. The following five danger signals require immediate vigilance:

The pointer of the water temperature gauge remains in the red zone continuously
Phenomenon: While driving, the water temperature gauge suddenly soars above 100℃, accompanied by a "boiling over" phenomenon.
Self-inspection steps

Stop the car immediately, turn off the engine and wait for 30 minutes to cool down.
Wear gloves and slowly unscrew the water tank cap to observe if there is any steam coming out.
Check the coolant level. If it is below the MIN line, it needs to be replenished.
Case: A car owner ignored the water temperature alarm and continued driving for 5 kilometers, resulting in the cylinder gasket being washed away. The repair cost exceeded 20,000 yuan.
Second, the cooling effect of the air conditioner drops sharply
Phenomenon: After turning on AC, the temperature at the air outlet is higher than 10℃, and the compressor starts and stops frequently.
Key points for investigation

Observe whether the fan operates synchronously when the air conditioner starts.
Use an infrared thermometer to measure the surface temperature of the radiator. If it exceeds 65℃, it indicates poor heat dissipation.
Check the signal of the air conditioning pressure switch. If the pressure is greater than 2.5MPa, the high-speed fan should be forcibly started.
Iii. Abnormal Noise
Performance

Metal friction sound: Failure of bearing lubrication.
Periodic humming: Blade deformation leads to dynamic balance disruption.
Sharp whistling: Short circuit of the motor winding.
Emergency response: Immediately turn off the engine to prevent the fan from getting completely stuck and causing the belt to break.
Four. The electronic fan operates continuously at high speed
Possible causes:

The temperature-controlled switch is stuck in the closed state.
The ECU received an incorrect temperature signal.
The contacts of the fan relay are burned out.
Testing method: Unplug the fan plug and measure the resistance value with a multimeter (normally it should be 20-50Ω).