5 Symptoms of a Bad Car Thermostat Valve and Replacement Cost

The internal combustion engine requires coolant to absorb its heat and keep its components cooled down. The proper amount of coolant must flow through the engine whenever it’s running in order to make this happen. A car thermostat is what manages the flow of coolant that goes into the engine. As soon as the engine gets warmer, the thermostat opens and allows coolant to enter the engine.

Once the engine has cooled off enough, the thermostat will close to restrict the flow of coolant into the engine. The thermostat also closes whenever your car is parked and the engine is idle because the engine is not working as hard to generate heat. Therefore, there is no need for coolant to enter it because the components of the engine are already cooled down.

5 Bad Symptoms

The car thermostat is basically like a temperature sensor for your engine. Once the thermostat goes bad, it is no longer able to sense the right temperature in your engine. This means it won’t open and close at the appropriate times to allow coolant into the engine. As a result, the engine will experience all sorts of temperature issues which could lead to worse symptoms.

Below are the top 5 symptoms of a bad car thermostat. Once you notice any of these symptoms, get your car thermostat replaced immediately.

1) Overheated Engine

An overheated engine is the most concerning symptom of a bad car thermostat. When coolant can’t reach the engine because the thermostat stays shut, it will cause the engine to overheat. You’ll notice this by looking at the temperature gauge on the dashboard. If the needle is in the red zone, then it means the engine is overheated. Replace the thermostat before the engine suffers permanent damage from this.

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2) Cabin Temperature Changes

When you control the air settings inside your vehicle, the temperature should stay pretty consistent with what those settings are. But when you have a bad car thermostat, the temperature inside the cabin will change suddenly. You might notice a huge drop in temperature and then a huge increase in temperature. These changes won’t even correspond to your air settings either.

3) Coolant Leak

A bad thermostat might stay shut, even when it’s not supposed to be. Coolant cannot enter the engine whenever this happens. Instead, the coolant will start to overflow and leak out of the thermostat housing area. As this problem escalates, the coolant hoses may leak too. You’ll notice the leak if you see green liquid coming out from underneath your vehicle.

4) Bad Heater

A bad car thermostat can cause the heater to malfunction. If your current environment is experiencing cold weather and you’re trying to warm yourself with your car heater, there may not be heat coming out if you have a bad car thermostat. This may be due to the thermostat staying in the open position and continuously allowing coolant to enter the engine.

5) Rumbling Sounds

Rumbling sounds will likely occur when you have a bad car thermostat. You’ll hear these sounds coming from your engine and/or radiator. You may also hear gurgling or knocking noises too. Don’t just ignore these sounds, especially if you’re experiencing any of the other symptoms on this list.

Replacement Cost

The replacement cost of a bad car thermostat should only be about $140 to $210. Of course, the make and model of your vehicle has a lot to do with the cost, but this is typically the average price range. The thermostat part alone costs around $30 to $60, while the labor costs are around $110 to $150. It shouldn’t take more than 1 to 2 hours for the auto technician to complete the replacement job.

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