Why is the temperature gauge fluctuating?

[DiValeria]

The unstable fluctuation of the temperature gauge is caused by a faulty coolant temperature sensor or a damaged thermostat. The engine coolant temperature, also known as the engine water temperature, may show erratic readings if the cooling system is malfunctioning. The main reasons for the temperature gauge's instability include: dirt accumulation on the contact surface between the coolant temperature sensor and the coolant; aging of the thermistor; abnormal operation of the voltage regulator; short circuit in the temperature gauge's heating coil; or an unstable thermostat that intermittently opens and closes, leading to fluctuating temperature readings. Specific explanations are as follows: Coolant temperature sensor failure: If the coolant temperature sensor fails or malfunctions, the engine ECU will detect an unreliable output signal and use a substitute value to protect the engine. This results in an unstable temperature gauge reading, often accompanied by difficulties in cold starts and poor acceleration. Thermostat damage: The thermostat automatically adjusts the flow of coolant into the radiator based on the coolant temperature, altering the coolant's circulation range to regulate the cooling system's efficiency and maintain the engine within an optimal temperature range. A damaged thermostat disrupts the engine's normal operating temperature, causing the temperature gauge to fluctuate.