What Causes Fluctuating Car Engine Coolant Temperature?

[OEverly]

Fluctuating car engine coolant temperature may be caused by faulty coolant temperature sensor; damaged thermostat; or cooling system malfunction. Below are relevant details about automotive coolant temperature sensors: 1. Introduction: The internal component of an automotive coolant temperature sensor exhibits higher resistance at lower temperatures and lower resistance at higher temperatures. Installed in the engine block or cylinder head water jacket, it directly contacts coolant to measure engine coolant temperature; 2. Working Principle: The Engine Control Unit (ECU) detects this resistance variation to determine coolant temperature. Higher resistance indicates lower temperature while lower resistance indicates higher temperature. The ECU uses this data to adjust fuel injection and ignition timing parameters.