Cooling Issues

Hello,

If the gauge is just simply going back and forth as you are just driving or idling, then it could be due to a faulty temperature sensor. It can also be due to a malfunctioning gauge.

The engine coolant temperature sensor is a thermistor (a resistor which changes value based on temperature). With as the temperature changes, so does the internal resistance of the sensor. That information gets sent to the ECM and that gets translated into the gauge readout.
Faulty sensor won't be able to provide correct resistance value and that will impact what the gauge displays.

I have attached the temperature and resistance value list below. Check the resistance between the pins on the sensor. If it does not fall within the specification, it needs to be replaced.

https://www.2carpros.com/articles/how-a-coolant-temperature-sensor-works

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.