What Causes Fluctuating Engine Coolant Temperature?

[LeAlexa]

Reasons for unstable coolant temperature gauge readings and fluctuating temperature: 1. Faulty coolant temperature sensor: Since the sensor is installed in the water jacket of the engine block or cylinder head and directly contacts the coolant to measure its temperature, a malfunctioning sensor will cause the engine ECU to use substitute values when it detects unreliable output signals. This protective measure for the engine results in unstable temperature gauge readings, often accompanied by difficulties in cold starts and acceleration. 2. Damaged thermostat: The thermostat automatically adjusts the flow of coolant into the radiator based on temperature, altering the coolant circulation range to regulate the cooling system's efficiency and maintain optimal engine operating temperature. You can check the thermostat by feeling the temperature difference between its inlet and outlet pipes. A faulty thermostat disrupts the engine's normal operating temperature, leading to unstable gauge readings.