What are the symptoms of a faulty car thermostat switch?
3 Answers
The symptoms of a faulty car thermostat switch: Due to the inability of the high-temperature engine coolant to dissipate heat, the water temperature will continue to rise. When it reaches a certain temperature, it can cause engine cylinder scoring, cylinder head deformation, and ultimately lead to the engine automatically shutting down. The thermostat switch is installed at the temperature-sensitive part of the radiator to dynamically collect the temperature changes of the water inside the radiator. It utilizes the principle of a bimetallic disc deforming under temperature and transient jumping at specific temperature points to provide safety protection for the car engine. When the coolant temperature continues to rise to 105 degrees, the high-speed contacts close due to the continued expansion of the wax, causing the radiator fan motor to operate at a high speed of 2400 rpm to increase cooling intensity. When the coolant temperature drops, the wax volume contracts, and the push rod retracts under the pull of the contacts, causing the contacts to open, thereby controlling the radiator fan motor.
In my twenty years of car repair experience, a faulty thermostat is particularly easy to spot. The most obvious sign is the erratic behavior of the coolant temperature gauge on the dashboard—today the needle stays stuck at the bottom, and tomorrow it suddenly jumps into the red zone. The radiator gurgles alarmingly, while the fan works overtime, spinning loudly right after starting the engine and failing to stop even after shutting it off. Once, I encountered a customer complaining that the heater blew cold air like an icebox—touching the radiator inlet hose revealed it was scalding hot, while the outlet hose was ice-cold, a sure sign the thermostat was stuck closed. If you notice abnormal coolant temperatures or no heat from the AC, check this little component immediately—engine overheating is no joke.
Last month I ran into this exact issue! While driving on the highway, I noticed the coolant temperature gauge kept hovering at the lowest mark, and the heater blew cold air even after running for half an hour. During the repair, the mechanic said the thermostat was stuck in the fully open position, causing the coolant to circulate continuously without allowing the engine to reach operating temperature. The funniest part was when the cooling fan suddenly went into overdrive while parked in the garage, draining the battery completely. The mechanic taught me a DIY diagnostic trick: After a cold start, feel both upper and lower radiator hoses - if they both get warm within five minutes, it's certain the thermostat has failed. After the repair, my fuel consumption dropped by nearly 0.5L/100km.
