What Causes the High Temperature Gauge When Turning on the Headlights?
2 Answers
The headlights have a separate ground wire (earth wire) and power supply line from the generator, while the temperature gauge and other instrument power supplies come from the positive terminal of the battery. Due to poor contact at the battery's negative terminal, the instrument power supply is in a low state. Below are the reasons for the high temperature gauge when turning on the headlights: Poor Contact of the Battery Ground Wire: Poor contact of the battery ground wire (earth wire) creates a voltage drop between the generator regulator's ground wire. When the headlights are turned on, the generator's load increases, causing the output voltage to drop. The voltage regulator then increases the output to normal voltage. At this point, the headlights' voltage is normal, and since the generator has already increased the output voltage, the battery terminal voltage also increases accordingly. This raises the power supply voltage to the temperature gauge, showing an increase in water temperature. Change in the Regulator's Reference Potential: Because the reference potentials for the instruments and the headlights are different, turning the headlights on or off changes the regulator's reference potential, resulting in different voltages across two unequal potential loads. The solution is to re-polish and tighten the battery's negative ground wire.
When the car's headlights are turned on, the water temperature gauge rises. I suspect it's because the sudden increase in electrical power consumption affects the overall system. When the headlights are on, the alternator has to work harder to supply power, increasing the current load and causing the engine to bear more burden. With higher engine load, the temperature naturally rises. If the cooling system can't keep up, the water temperature gauge starts to climb. The most common issue is that the cooling fan is electrically driven. If the power supply is unstable or the control module malfunctions when the headlights are on, the fan speed may slow down or even stop, failing to cool the radiator in time. I've experienced similar situations with multiple cars. After parking, I checked and found the fan spinning as slow as a snail. Sometimes it's due to an aging alternator outputting abnormal voltage. Quickly take it to a repair shop and have the mechanic test the output voltage and fan control wiring. Don't wait until the engine overheats and gets damaged. Remember to regularly maintain electrical components and keep the fan motor clean and rust-free.
