Test Car Thermostat Without Removing, The Symptoms of a Bad Thermostat

A bad thermostat is surely big trouble for the car owner. The reason why it is very exhausting to test a thermostat is that it is commonly concealed below the other engine parts. And even if you exert more effort digging your way to its location, removing it simply implies messy work and splashing some antifreeze during the process. You may wonder – is there a better way to do it? Can you test car thermostat without removing it?

Well, many have learned from old technicians that there is a better way of testing the thermostat and it does not involve removing it.


A thermostat is one of the most essential components when running a car. It plays an important role as it takes charge in controlling the flow of the coolant when operating the vehicle. The thermostat can either be in the open or close phase.

If the engine is shut off and it is in cooled condition, the thermostat is set into a close phase. However, if the engine is running and reaches a specific temperature, it is set into an open phase. The thermostat will be in the open phase once the coolant circulates and from the car’s radiator as it reduces the temperature. This particular circulation guarantees that the engine is functioning at its anticipated temperature.

If the thermostat becomes faulty, you cannot expect the coolant to effectively flow. It is either set in an open or close position. If it occurs in an open position, the coolant will continually circulate causing the temperature to not reach its ultimate heat level. Else ways, if it occurs in a close position, the coolant cannot traverse through the radiator to the engine. Either it occurs in an open or close position; they are both bad and may lead to developing issues.

You can determine a bad thermostat by knowing its symptoms. Below are indications that you must watch out for:

Overheated Temperature Gauge

An overheated temperature gauge is the first thing you should watch out for. If you notice the temperature of the gauge to be extremely high when running your car, then it could mean that your thermostat is faulty.

Variations in Temperature

When starting the car, you should see the gauge in the Cold part if the vehicle has been put into the park for a while. While you are driving, you will usually see the gauge slowly gains on until such time that it reaches the midway section in the gauge, which is considered to be the best temperature for the engine operation.

When the thermostat is in a stuck closed position, the coolant is prevented from circulating into the engine. This implies that that temperature gauge will keep on going higher until it reaches the Hot end. If you keep on driving the car in that particular condition, there would be a greater chance of engine damage.

This is the reason why you should always check the engine temperature gauge. The moment you notice that the temperature gets higher than usual, it would be best if you pull over to let the engine cool down.

In the event that the thermostat is in a stuck open position, you will see that the temperature goes up more gradually than usual and seemingly stops before it returns to its midpoint status. If you happen to see this, consider cranking up the heater. If it will not rush warm air from the vents, it is certain that your thermostat is broken.

Cracks around the Thermostat

One of the bad thermostat symptoms is a leaking coolant. You will commonly notice the leak close to the thermostat’s housing. If the thermostat is closed, it will begin leaking on the ground beneath the car.

Malfunctioning heater

If you are driving during winter or you are living in a place with a cooler climate, you may experience a contradicting temperature issue in your car. Rather than being stuck closed, the thermostat will be stuck open. This implies that it will allow the coolant to continuously circulate in the engine even if the engine does not require it. Thus, if you turn on the heater and the thermostat is in an open position, then the cool air keeps on coming out of the vents despite turning up the heater.

Abrupt changes in air temperature

One indication that you will frequently feel is once the air temperature in the car abruptly changes. It may begin by falling to an extremely low temperature, then abruptly goes up to an extremely high temperature.

Any shift in air temperature that does not emulate your existing HVAC settings will normally signify that there is a problem with the thermostat.

Roaring noises

If changes in temperature were not that bad, you will start hearing weird roaring noises. These sounds can come from the engine, radiator, or both. The noises may also be similar to a boiling sound, gurgling sound, or knocking sound. Essentially, if you notice these weird noises, then there is a good chance that your thermostat is faulty.

How to Test Car Thermostat without Removing?

You can test the car thermostat without removing it by familiarizing the following tips:

  • Put your car into the park and lift the hood. Set the brake-in emergency. Closely monitor the gauge as you warm up the engine. After several minutes, you will see that the temperature goes high while the engine is operating.

    Once the engine light is on and at the same time the temperature reaches a warning in your gauge, the thermostat is closed. If the temperature begins going high and you notice that the top portion of the engine creates steam, the thermostat is stuck closed.
  • The moment the engine has cooled down, detach the radiator cap and run it again. Check the opening part of the radiator cap to check the coolant and temperature gauge. The choke opens once the engine achieves its anticipated temperature. Circulation within the radiator happens. That is evidence that the thermostat is allowing circulation to occur. However, if the circulation does not properly occur, then it could mean that there is a problem with the thermostat.
  • Lift the hood and set the break-in emergency. When the temperature gauge is extremely hot and you notice any swirling sound coming from the radiator tank, it could imply that the thermostat is taking the opening and closing phase. It is allowing the coolant to circulate back and forth the tank.
  • Run the engine of the car to make it reach its normal temperature. Then allow the dashboard heater control to attain its highest temperature while having the fan on its complete power. Wait for several minutes to normalize the temperature. During this time, the heat coming from the vents becomes obvious. The temperate is either a bit warm or hot. Nevertheless, after a few minutes if the air is warm or cool and the gauge sets below the usual, then you should know that it is stuck open. This implies that the circulation of the coolant is quicker than usual. You have to replace it.

FAQ

Can a bad thermostat be fixed?

  • Unfortunately, you cannot fix a bad thermostat. And if ever you could, it would be non-sense to do it because they are more affordable to purchase than fix.

Is it difficult to replace a thermostat?

  • The level of difficulty in replacing a thermostat relies on the kind of car and the added steps required in reaching the thermostat. If the thermostat is accessed easily, then replacing it quite easy and will not exceed 30 minutes to finish.

Final Thoughts

A thermostat serves as the car’s cooling system; thus it is very important that it functions efficiently. A vehicle that is either stuck in the open or close phase can lead to inconvenience not just to you but also to the driver and the passengers. it is essential that you make sure that the car is in good condition.

One way of maintaining the condition of your car is by monitoring the status of your thermostat. To easily do it, you should learn how to test car thermostat without removing it.


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