Symptoms of a Bad or Failing Thermostat

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A car thermostat regulates the flow of coolant through the engine and is an incredibly important player in the operation of your vehicle’s engine. You may hear the phrase “the thermostat was stuck open or closed.” When the engine has been sitting for a while and is not warm, the thermostat will be closed. Once the engine is running and reaches a certain operating temperature, a sensor inside the thermostat will cause it to open, allowing coolant to flow to and from the radiator, decreasing the temperature so it can be recirculated through the engine again. This constant flow (in conjunction with several other cooling system components) keeps your vehicle’s engine functioning at the optimum temperature.

The opening and closing of the thermostat at the correct time are critical to maintaining proper engine temperature. In the event the thermostat happens to become “stuck” closed, there is no way for coolant to be circulated through the radiator and eventually back through the engine, which causes extremely hot engine temperatures. Likewise, if the thermostat is “stuck” open, the flow of coolant is constant, it results in the vehicle’s engine temperature never reaching an optimum level of heat, creating performance problems and accelerating the wear-down of parts. There are 4 common symptoms associated with a bad or failing thermostat.

1. High-Temperature Reading and Engine Overheating

The first and potentially most alarming symptom will be the temperature gauge reading high into the red within the first 15 minutes of your vehicle engine running. This is often the first sign that the thermostat is not functioning properly. It means coolant isn’t entering the engine because the thermostat is stuck closed, and your car can suffer engine damage fast.

2. Low-Temperature Reading and Underheated Engine

A thermostat stuck in the open position constantly pushes coolant into the engine and causes a lower operating temperature. Your temperature gauge will show a needle that barely increases or remains at the lowest setting. This will reduce engine efficiency and increase emisssions over time, as well as accelerate the deterioration of parts.

2. Temperature Changing Erratically

Erratic temperature fluctuations can also occur, causing dramatic spikes and drops in temperature that eventually lead to poor engine performance and reduced gas mileage. In this case, you may see the temperature abnormally low at one point and, shortly after, climb to an abnormally high level. The thermostat itself isn’t stuck in any one position, but it will still produce false readings and cause issues with coolant regulation.

4. Coolant Leaks Around Thermostat Housing or Under Vehicle

Another indication may be leaking coolant, which can occur when the thermostat does not allow coolant to flow when stuck in the closed position. This can be noticeable in a variety of locations, but most commonly around the thermostat housing. It can eventually cause other coolant hoses to leak as well, often resulting in coolant leaking on the ground under your vehicle.

Thermostat replacement is a fairly inexpensive repair to make to your vehicle, preventing potentially thousands of dollars in engine damage due to excessive heat. If any of the above symptoms sound familiar to you, it may be time to have an expert mechanic diagnose your vehicle.


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Thomas

11 years of experience
72 reviews
Thomas
11 years of experience
Ford Mustang - Car is overheating - Titusville, Florida
Thomas was great! Very knowledgeable and honest. Went above and beyond to perform his duties for his job. I will definitely get Thomas again, and trust any car I habe to him.
Ford Fiesta - Car is overheating - Orlando, Florida
Thomas was on time and friendly. He explained his findings in a way that made me feel confident in making a repair decision. I will would absolutely recommend Thomas and I will be using him in the near future.

Gustavo

15 years of experience
44 reviews
Gustavo
15 years of experience
Honda Odyssey - Car is overheating - New Braunfels, Texas
Gustavo was very professional came on time diagnosed our van told us what the problems were and was very kind and professional about definitely recommend him 
Ford Focus - Car is overheating - San Marcos, Texas
He was efficient in checking for the cause of my car overheating. Offered me the best cost friendly solution after the inspection to help me get back on the road.

Chris

16 years of experience
337 reviews
Chris
16 years of experience
Mazda 6 - Car is overheating - Pearland, Texas
I thank Chris for his Professionaal attention that gave to me and my daughter concerning her car repair. Looking forward for him to repair her car and praying that the problem will be fixed.
Ford Edge - Car is overheating - Houston, Texas
Chris was very helpful and thorough in finding out and explaining what was really wrong with my truck.

Lee

36 years of experience
82 reviews
Lee
36 years of experience
Saturn Sky - Car is overheating Inspection - Edmond, Oklahoma
Lee is just fantastic so friendly and so knowledgeable no one is better trust me thank you very much Lee

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