How can I check if my car’s thermostat is working?

Yesterday, my car’s engine was making a weird sound, and the temperature gauge was almost in the red zone. Like most college students who don’t know what to do, I called my parents, and they said my car’s thermostat could be broken. How can I check if my car’s thermostat is working?

Your parents are correct that a broken car thermostat could be the cause of your problems. Fortunately, there is a pretty simple way to check, but driving with an overheated engine can lead to severe damage, so avoid driving until you see a mechanic.
The thermostat in your car controls the flow of coolant to your engine, so when broken or faulty, drivers tend to experience:
  • Engine overheating
  • Abnormal changes in the engine or cabin temperature
  • Roaring noises
  • A malfunctioning heater
To check if your car thermostat is working, do the following:
  • Allow your engine to completely cool, open the hood, and remove the radiator cap. The radiator is usually a narrow silver or black box and will have a metal cap on top.
  • Start the engine and let it idle for 10 to 20 minutes.
  • Observe the coolant in your radiator as the engine warms up.
  • If coolant starts flowing immediately, your thermostat is likely stuck open.
  • Once warm, if no coolant is flowing and the temperature gauge passes the midway point, your thermostat is likely stuck closed.
If you’ve determined that the thermostat is not working, you’ll need to replace it. Replacing a thermostat isn’t too difficult but does require some know-how and time, so it may be best to call a professional.
Many aspects of car ownership are best left to professionals, and your car insurance is no different. If you want to save money on your insurance or need some advice on coverage options, download the Jerry app. A licensed broker, Jerry does all the hard work of finding cheap quotes from the top name-brand insurance companies and buying new car insurance. Jerry’s friendly agents are just a text away and will even help you cancel your old policy!
Jack Walsh
Answered on Nov 15, 2021

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