How to know if thermostat is bad in car – A guide

How to Know Thermostat is Bad in Car

What does a thermostat do, you ask? The thermostat of your car works in conjunction with the radiator and coolant to keep your engine at an appropriate temperature. Temperature sensors are an integral part of the radiator system flow when the thermostat is working properly. The thermostat permits warm coolant to enter the radiator to keep the engine from overheating. Your thermostat may be to blame if you’re experiencing overheating troubles. 

How to Know if Vehicle Thermostat Is Bad

The question is, how to test if the thermostat is bad in the car? The following are warning signals that it’s time to get a new one:

Above Normal Temperatures of 

Above normal temperature is one of the bad thermostat symptoms. If the temperature inside your car is consistently rising, it’s possible that your car thermostat needs to be replaced. Cars can get hot and possibly overheat; this is not unheard of. Having the automobile serviced or re-filling the coolant usually fixes or alleviates the overheating problem. You have a problem when the temperature rises quickly and doesn’t go down no matter what you try.

High temperatures can be a low coolant symptom of a tiny leak in the coolant tank or a malfunctioning thermostat. One approach to tell if the thermostat is the problem is to look for sudden temperature changes. The thermostat may be to blame if, when you start the automobile, the engine temperature is low but quickly rises.

Freezing Engine 

If your car’s thermostat has failed, it is widely believed that your engine is always overheating. This is not the only case. One clue that something’s wrong with your thermostat is that it could simply start running cold. As a result, your car’s performance might get affected by a malfunctioning thermostat.

Maintaining a constant flow of hot coolant to the radiator is the primary purpose of the thermostat. The thermostat aids in the cooling of the coolant to prevent the engine from overheating. However, even if the coolant is cold, if the thermostat is left open, it will continue to flow. Because of this, the car’s engine might freeze over time, which might lead to mechanical problems.

 How to Know if Thermostat is Bad in Car

Temperature Gauge Problems  

The quickest approach to determine whether or not your thermostat needs to be replaced is to check the temperature gauge yourself. To remove the thermostat, you’ll need a pair of needle-nose pliers.

Make sure the water in the bowl you’re going to put the thermostat in is hot before you do anything else to avoid scorching the thermostat. As soon as you submerge your thermostat in water, keep a close eye on its temperature. You may require a new thermostat if the temperature gauge does not rise, or if it spikes or rises well over the real water temperature.

Coolant Level Problems

The coolant levels should be checked if you begin to experience problems with the thermostat. When you add coolant to the tank, take note of where the coolant level drops. There should be a fill line on the side of the coolant tank, or some other means to see how much coolant is left in the tank. Make a note of when you last refilled the coolant and the current level.

Your thermostat may be malfunctioning if the coolant levels fluctuate significantly. You should notice a gradual drop in your blood pressure. If the tank is empty, you may have a leak or a thermostat problem. If you don’t see any change, it’s possible that your thermostat is stuck closed.

Visit an Automotive Center if you suspect that your car’s thermostat isn’t operating properly. You need to perform a comprehensive diagnostic on your vehicle, including the thermostat, to find out what is wrong and what needs to be repaired or replaced.

thermostat in car

Changing or Testing a Thermostat’s Settings

It’s not difficult to check (and, if necessary, replace) a thermostat. However, you should take a few measures first. 

  • Never attempt to open your car’s cooling system while the engine is running; doing so will leave you with permanent scars. 
  • There is a gasket that seals the housing and we strongly advise against re-using it because it may not even come out in one piece. Wait for the engine to cool down, have rags on hand, and check if it needs a sealant. This shouldn’t take more than a few minutes of your time to order the correct gasket. 

The thermostat is usually positioned around the top of the engine on most automobiles. In other cases, you may have to crawl under the car to get to it, especially if you drive a Subaru. To get to the thermostat, begin by removing the hose from the thermostat housing, loosening and then removing the bolts that hold the top half of the housing in place. Once this is done, you’ll be able to see the thermostat. Remove it and carefully scrape off any remaining gunk from the gaskets. It’s as simple as replacing the thermostat with a new one, installing the new gasket, tightening the bolts, and reinstalling the hose. Make a beeline for the kitchen if you’re unsure.


  • How long does it take a car to cool down?

An overheated engine must be left to cool down for at least 30 minutes before it can be inspected and perhaps repaired.

  • How does a car act when the thermostat is bad?

A damaged thermostat will cause odd temperature fluctuations when the engine is running. However, even if the thermostat does not become stuck, incorrect readings will continue to cause problems with the control system. Instabilities in engine temperature and radiator coolant flow will occur.

  • How can I test my thermostat without removing it?

Start the engine of your car and let it run for a few minutes. See if the coolant is flowing through the radiator filler neck. Until your car reaches a temperature where the thermostat opens, it should not be flowing. The thermostat valve is open if you see coolant flowing.

  • How do I know if my coolant is circulating?

Touch the bottom radiator hose after the engine has warmed up. It’s safe to assume that coolant is circulating if you can feel the lower hose getting warm. The radiator may be inhibited if the bottom hose is not hot.

  • Can low coolant affect acceleration?

In cold weather, the thermostat remains closed, preventing the coolant from being recirculated. It keeps the car warm. Overheating, which can damage the engine, can cause a lack of acceleration in some situations.

  • Does the car need to be running when adding coolant?

Yes, you need to start the engine. After draining the coolant, you will either have a precise procedure for removing air from the cooling system or you will simply run the engine. If you don’t, as the engine heats up, the gasses (air) will expand at a rate greater than liquid.

Final Word

And that’s a wrap on how to diagnose a bad thermostat in a car. Make sure to keep your thermostat up to date; otherwise, it might cause problems.