What Causes the Thermostat to Fail to Open?
3 Answers
The reasons why the thermostat fails to open: 1. The thermostat is damaged and cannot open, which is the most common and serious issue; 2. The coolant temperature is too low to reach the opening temperature, leading to failure to open, which is also relatively common; 3. Prolonged disuse causes rust and sticking, though this is less frequent. Here are the relevant details: Function of the thermostat: It automatically adjusts the amount of coolant entering the radiator based on the coolant temperature, altering the circulation range to regulate the cooling system's capacity, ensuring the engine operates within the appropriate temperature range. Maintenance status: The thermostat must be kept in good technical condition; otherwise, it will severely affect the engine's normal operation. For example, if the main valve opens too late, it can cause engine overheating; if it opens too early, the engine's warm-up time will be prolonged, resulting in the engine temperature being too low.
Last time my car's temperature gauge suddenly spiked into the red zone, and I found out it was due to a stuck thermostat. This component acts like the goalkeeper of the cooling system—when it fails to open as it should, the coolant can only circulate within the engine's small loop, completely bypassing the radiator. Common causes include jammed mechanical parts, failed thermal sensing wax pellets, or water pipe scale clogging the valve. Never force the engine to run under these conditions—engine temperatures above 90°C can cause deformation! Once when this happened to me on the road, I immediately pulled over, turned off the engine, and opened the hood to let it cool for half an hour before daring to add water. This issue can also cause collateral damage to the water pump and cylinder head gasket, so it's best to replace the coolant during repairs.
A thermostat that fails to open will directly cause engine overheating. I've seen too many cars in repair shops that ended up needing major overhauls due to neglecting this small component. There are mainly three reasons: the internal spring of the thermostat breaks or the wax actuator gets stuck; the temperature-sensing element ages and can no longer detect temperature changes; or the water passage gets blocked, preventing the valve from moving. In daily use, you can judge by feeling the temperature difference between the upper and lower radiator hoses—if the lower hose doesn't get hot after idling for ten minutes, you've got a problem. In an emergency, try gently tapping the thermostat housing; with luck, you might dislodge a stuck valve. However, the permanent solution is to replace it with a new part, and when doing so, make sure to clean the water passages.
