Car Maintenance

What does an autothermostat do?

When you turn on your car engine, it spontaneously builds up heat. This is a normal gradient (a good sign that it’s working). When you drive your car for a period of time, the engine heats up. The moment you shut it down, it also gradually cools down.

Depending on the activity, your engine would heat up or cool down. However, your engine alone does not “know” when it is overheating. To maintain the optimal temperature suitable for your engine, you need an autothermostat.


Thermostats are located between your vehicle’s engine and radiator. Most often found in kits fitted to modern cars, the autothermostat’s primary function is as a “control center” that regulates the amount and flow of coolant entering the engine.

cooling system

Your car engine operates based on an optimal temperature range (typically around 2000F). As the saying goes, “Too much of anything is bad.” If your engine overheats, it will perform poorly or, worse, be damaged. Because of this, coolant helps regulate the optimal engine temperature. Once your engine gets hot, the autothermostat will allow coolant to flow and cool the engine.

allow heat to build up

Aside from that, the autothermostat also ensures that your engine reaches the ideal operating temperature as quickly as possible (so it blocks the flow of coolant any time your engine is still building up heat). This is an important feature to maximize the performance and potential of your engine. It also reduces emissions of other harmful chemicals and unwanted engine wear.

How do car thermostats work?

The magic of your car thermostat is the tiny cylinder (with a rod that connects to the coolant valve) that is placed on the side of the engine. This device acts as your temperature sensor. It is filled with a wax pellet that melts when the temperature reaches around 1800F. Each time it melts, it expands and pushes the rod, which in turn opens the coolant valve. This device is basically the backbone of your entire cooling system.

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What are the most common car thermostat problems?

Although not always the case, car thermostat problems do occur from time to time. One of the earliest signs would be that your engine is overheating shortly after running.

In general, two problems arise from a stuck thermostat – be it in the closed or open position.

Stuck in open position

The continuous uncontrolled flow of coolant, which leads to a drastic reduction in engine temperature. This prevents wear and tear on your engine. If you find that your engine is taking a long time to warm up, a bad thermostat is likely one of the reasons for the excessive coolant flow.

Stuck in closed position

This is the opposite of the first. If stuck in the closed position, it would not release coolant, which would then lead to overheating (and worse, self-destruct).

Cause of erratic engine temperature

Aside from your car thermostat, erratic engine temperature can also be due to other issues. Below are some of the most common reasons for this problem.

  • Clogged radiator and defective radiator fan
  • Leaks in the cooling system
  • Low coolant level
  • Defective water pump / bad water pump belt
  • Defective radiator hose

How to check your car thermostat

If you’re still unsure of the reasons for your erratic engine temperature, you can always perform a quick thermostat check to spot any potential problems.

  1. Check if your engine and radiator are cool enough to be checked. You don’t want to get any first degree burns.
  2. Find the thermostat under your hood. Just follow the upper radiator hose towards the engine as its end connects to the thermostat housing. In general, the car thermostat is also located in the housing.
  3. Check your thermostat. You can easily do this by removing the radiator cap to see the coolant flow. Crank the engine for a few minutes to start it. Examine the neck of your radiator filler neck to see coolant flow. Since your car has not yet reached its optimal operating temperature, the coolant should not be flowing. If it’s flowing, that just means your valve is open. In most cases, you will need to replace your thermostat to fix this problem.
  4. If the coolant is not flowing, wait longer for your engine to warm up and reach operating temperature. If your temp gauge starts to rise and your coolant is still not flowing, it means your valve is stuck in a closed position.
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How to replace your car thermostat

This is a general guide to replacing your car’s thermostat in the event of a problem.

  1. Double check that your engine and radiator are cool enough to be checked.
  2. Remove the radiator hose from the hood by pulling off the clamp.
  3. Remove the hose. Prepare a rag as excess coolant would likely drip off.
  4. Unscrew the screws that secure the thermostat. Remove the old thermostat.
  5. Remove the remaining gasket from the housing. Wipe everything down with a clean, dry cloth.
  6. Install the new thermostat. You can also add more engine coolant if your levels are low. After that, reinstall all the removed items including the screws, hose and radiator hose clamp.
  7. To determine if your installation is successful, start up your engine and observe its build up until it reaches operating temperature.
  8. If your first test shows no problem, take your car for a test drive. Always check the temperature gauge needle while driving with your new thermostat to see if things remain stable and normal. Don’t forget to enjoy your ride!


All in all, running your car engine when it is too cold or too hot would result in poor performance and damage. It causes engine malfunctions, wear and tear, emission of pollutants to name a few. To solve this problem, your car thermostat maintains the optimal temperature for your car. It regulates the coolant flow and ensures that your engine runs in the optimally set temperature range.

Chloe Rimmer
Tv geek. Content practitioner. Creator. Wannabe beer nerd. Thinker. Passionate explorer. Proud bacon trailblazer. Travel fanatic. Award-winning introvert.

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