What Does It Mean When the Temperature Gauge Is Normal but the Red Light Is On?
3 Answers
The temperature gauge is normal but the red light is on, which is generally a false alarm of the coolant temperature warning light. When the owner adds antifreeze, due to the excessively low position of the vent hole on the side of the reservoir damping tube, compressed air columns form inside the damping tube. This causes the liquid level in the damping tube to be significantly lower than that in the expansion tank and close to the sensor's alarm point. Vibration during driving can easily trigger a false alarm. Below is an introduction to the temperature gauge: 1. Normal Temperature: The coolant temperature typically displays between 70-90°C after the engine warms up, which is normal. When the coolant level in the radiator is low, the temperature will rise, and water needs to be added. If the temperature gauge approaches the 'H' or the red danger zone, and the coolant temperature warning light comes on in severe cases, it indicates that the engine coolant temperature is too high. 2. Working Principle: The temperature gauge sensor is a thermistor-type sensor fixed with threads on the engine coolant passage. The thermistor determines the current flowing through the coil windings of the temperature gauge, thereby driving the pointer to swing.
Oh, I've encountered the situation where the coolant temperature warning light comes on but the temperature gauge shows normal readings. Last month, my old Corolla had this exact issue: it was most likely a faulty coolant temperature sensor or poor connector contact. The car's computer receives false signals, causing erroneous alarms. You should immediately pull over safely, turn on hazard lights, and feel the upper radiator hose with your hand - if it's not scalding hot, it means the actual coolant temperature isn't really high. Another possibility could be unstable battery voltage causing the ECU to malfunction and give false alarms. In my case, I simply unplugged and firmly reconnected the sensor connector to fix it. Of course, it might also be caused by a short circuit in the instrument panel wiring. If the warning light remains on after restarting, never force the car to keep running.
Last week I personally experienced a similar situation: the temperature gauge needle was steady at the midline, but the red warning light was glaring. Don't panic and call for a tow truck just yet! Upon opening the hood, I found the coolant reservoir level had dropped below the minimum line—the level sensor had triggered the alarm. After topping up with blue coolant, the red light turned off by itself within five minutes. If the fluid level is normal, then check the electrical connectors, especially the wiring harness near the radiator at the front of the car, as it's prone to rodent damage. Also, in some older vehicles, oxidized ground wires can cause the alarm system to act up. Remember to check if the alternator voltage is stable.
