What is the function of a thermostat?
3 Answers
The function of a thermostat is to automatically regulate the amount of water entering the radiator based on changes in coolant temperature, while also altering the circulation range of the water. This achieves the adjustment of the cooling system's heat dissipation capacity, thereby ensuring the engine operates within an appropriate temperature range. A thermostat is a valve that controls the flow path of the coolant, serving as an automatic temperature-regulating device. It typically contains a temperature-sensitive component that opens or closes the flow of air, gas, or liquid through thermal expansion or contraction. The thermostat must maintain good technical condition; otherwise, it can severely affect the normal operation of the engine. For instance, if the main valve of the thermostat opens too late, it can cause the engine to overheat. Conversely, if the main valve opens too early, it prolongs the engine's warm-up time, resulting in the engine temperature being too low.
Last time I modified my engine, I did some research on the thermostat. This little gadget acts like a smart switch for the cooling system. Normally, it keeps the coolant circulating in a small loop inside the engine to warm up quickly. Once the coolant temperature reaches around 90 degrees, the valve opens, allowing the coolant to flow through the radiator for a larger cooling cycle. If the thermostat gets stuck in the closed position, you'll see the engine overheating alarm go off in no time, while the radiator stays ice-cold. On the other hand, if it's stuck wide open, you won’t get warm air in winter, and the engine will take forever to warm up. Inside, it has special wax that expands when heated to push the valve open—a pretty clever design. Repair shops often see owners replacing water pumps unnecessarily due to thermostat failure. Before tearing anything apart, always check the temperature difference between the upper and lower radiator hoses to diagnose the issue.
I remember once during a long-distance drive, the temperature gauge suddenly shot up to the red zone. Upon inspection, it turned out that the thermostat valve was stuck and couldn't open due to scale buildup. This component, about the size of a fist, plays a critical role—it monitors the engine temperature like a traffic cop directing the coolant flow. When the engine is cold, it closes the small circulation loop to allow the engine to warm up; once the temperature reaches the optimal level, it opens the large circulation channel. Many people aren't aware that the engine has two sets of coolant passages, all controlled by the thermostat. Diagnosing a faulty thermostat is straightforward: after a cold start, feel the upper radiator hose—if it heats up within five minutes, the valve isn't sealing properly. If the engine runs too cool at highway speeds and the heater doesn't produce enough warmth, there's an 80% chance the valve is stuck open. When replacing it, it's best to opt for a complete assembly with a sealing ring.
