What is the reason for the normal temperature gauge but the red light is on?
2 Answers
The normal temperature gauge but the red light is on is caused by a false alarm of the 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, a compressed air column forms in the damping tube, causing the liquid level in the damping tube to be much lower than that in the expansion tank and near the sensor alarm point. The vibration during driving can easily trigger a false alarm. Here is some information about the temperature gauge: Normal temperature: The temperature gauge shows the coolant temperature, typically displaying 70-90 degrees after the engine warms up, which is normal. When the water level in the coolant tank 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 temperature warning light comes on in severe cases, it indicates that the engine coolant temperature is too high. Working principle: The sensor of the temperature gauge is a thermistor-type sensor, fixed with threads on the engine coolant passage. The thermistor determines the current flowing through the coil winding of the temperature gauge, thereby driving the pointer to swing.
The car's temperature gauge shows normal but the red warning light is on. I've encountered this strange situation a few times. Usually, it's not that the engine is actually overheating, but rather a malfunction in the warning system. Possible causes include issues with the signal wire of the coolant temperature sensor—it sends normal data to the gauge, but the part connected to the warning light may have a short circuit or poor contact, triggering a false alarm. It could also be a fault with the warning light bulb itself, such as aged wiring causing intermittent connections when driving on bumpy roads. Additionally, check the coolant level; sometimes the level is low, but the gauge doesn't respond quickly enough, causing the light to warn as a precaution. For safety, as soon as you see the light come on, stop driving and pull over to a safe place to inspect. If there really is a problem, it could damage the engine. It's recommended to first manually check the coolant level and the operation of the cooling fan. If that doesn't resolve the issue, take it to a repair shop to use a diagnostic tool to check the electrical circuits.
