How to Determine if a Car's Thermostat is Faulty?
2 Answers
If the engine's warm-up time is significantly slower than before, and you notice a noticeable decrease in the car's power, it's necessary to check whether the fan is operating normally. If the fan is functioning properly, and when the engine temperature is excessively high, the coolant temperature in the radiator is not high, and touching the radiator by hand doesn't feel hot, then it's highly likely that the thermostat is faulty. Symptoms of a faulty thermostat include: 1. The main valve of the thermostat remains closed for a long time. If the main valve of the thermostat remains closed for an extended period, it naturally loses its automatic function of regulating coolant flow. 2. The thermostat remains open for a long time. If the thermostat stays open for a prolonged period, it's equivalent to removing the thermostat, causing the engine's operating temperature to be lower than usual. This affects the engine's thermal efficiency, leading to insufficient car power.
If you have years of hands-on experience tinkering with cars like I do, diagnosing a faulty thermostat is actually quite straightforward. I usually start by keeping an eye on the temperature gauge—if the engine temperature struggles to rise or spikes too quickly after running, there’s definitely an issue. Next, pop the hood and feel the radiator hoses: if the upper hose is scalding hot while the lower one stays ice-cold, it means the thermostat is stuck closed, blocking coolant flow. The heating system can also be affected—weak or inconsistent cabin heat is another red flag. I recommend checking the coolant level regularly; low fluid could indicate a leak caused by a worn thermostat seal. Safety first—an overheated engine blowing up mid-drive is a nightmare, so I make it a habit to do basic checks monthly as prevention. It’s wise to keep an OBD scanner handy to read trouble codes; without professional tools, just drive to a mechanic for testing—DIY fixes often backfire. Bottom line: knowing car maintenance helps your ride last longer.
