Symptoms of bad Thermostat
A bad thermostat causes your engine to become too hot. This is because the thermostat is a small "gatekeeper" that decides when to let coolant flow and when to keep it out on the engine; this way, it prevents the engine from becoming too hot or too cold. The thermostat is a small valve-y component between the engine and the radiator, inside a housing. Let's see the most common symptoms of a bad thermostat:
One of the most common signs of a bad thermostat is engine overheating. If the thermostat gets stuck in the closed position, it prevents coolant from flowing to the radiator, causing the engine to overheat quickly. You might notice the temperature gauge climbing into the red zone or even see steam coming from under the hood. Ignoring this can lead to serious engine damage like a blown head gasket or warped cylinders.
2. Engine Running Too Cold
A thermostat stuck in the open position causes the engine to run cooler than normal. While this might sound harmless, it can lead to poor fuel efficiency and increased emissions because the engine never reaches its optimal operating temperature. You may notice the temperature gauge staying low even after driving for a while, and the cabin heater may blow cold air despite the engine running.
3. Fluctuating Temperature Gauge
If your temperature gauge constantly moves up and down, it could be a sign of a failing thermostat that’s opening and closing erratically. The inconsistent flow of coolant can cause the engine temperature to fluctuate unexpectedly, leading to unpredictable performance and potential overheating.
A bad thermostat can cause pressure buildup in the cooling system, leading to coolant leaks around the thermostat housing, radiator, or hoses. You might see puddles of coolant under the car or notice a sweet smell coming from the engine bay. Leaking coolant can quickly lead to low coolant levels, increasing the risk of overheating.
If your car’s heater blows cold air when it should be warm, the thermostat could be stuck open, preventing the engine from warming up properly. Since the heater relies on hot coolant from the engine, a thermostat that doesn’t allow the engine to reach its proper temperature will lead to poor cabin heating.
6. Increased Fuel Consumption
A thermostat stuck open can cause the engine to run colder than designed, forcing it to use more fuel to maintain performance. The engine control unit (ECU) will compensate for the cooler temperature by injecting more fuel, leading to reduced fuel efficiency and increased emissions.
If the thermostat is malfunctioning, you might hear gurgling or rumbling noises from the radiator or engine bay. This can be caused by trapped air in the cooling system or coolant boiling due to improper circulation. These noises usually indicate that the coolant isn’t flowing as it should.
A failing thermostat can trigger the Check Engine Light if the engine temperature is too high or too low for extended periods. Modern vehicles have sensors that monitor engine temperature, and any irregularities can prompt the ECU to log a trouble code related to the cooling system. A diagnostic scan tool can help confirm if the thermostat is the issue.
9. Radiator Hose Temperature Difference
If you suspect a thermostat problem, you can check the temperature difference between the upper and lower radiator hoses. If one hose is hot and the other is cold, it’s a sign that coolant isn’t circulating properly, likely due to a stuck thermostat.
