How To Prevent Air Bubbles From Getting Into Your Car’s Cooling System


A car’s cooling system ensures that the engine and other components do not overheat. After all, a combustion engine generates so much heat that it can destroy itself were it not for the cooling system. But, unfortunately, that system is put at risk when air bubbles find their way inside.

You can prevent air bubbles from getting trapped in a car’s cooling system by topping-up coolant regularly and changing it when it gets old. It’s also crucial to bleed out any trapped air after pouring coolant in. Faulty components like thermostats must be replaced quickly, and the occasional system flushing helps. Above all, regular inspections keep your cooling system healthy and bubble-free.

This guide will walk you through several ways you can prevent air bubbles from getting into your car’s cooling system. Plus, you’ll learn how that air got in there in the first place and what happens if you don’t get them out.

Related: Why Radiator Keeps Pushing Water Out?

How Does Air Get Into The Car’s Cooling System?

Air bubbles are a significant threat to your car’s cooling system. So, it’s crucial to understand how they find their way inside the system in the first place.

Here’s how air bubbles get into a car’s cooling system:

  • Leaks: Your car’s cooling system consists of a reservoir, several hoses or pipes, and the necessary components. The system is sealed to prevent air from getting in, but leaks in parts like the hoses are common. Air will enter the system through those leaks.
  • Faulty Components: The cooling system has components that regulate air flow outward. Unfortunately, defective parts fail to regulate that airflow, allowing air to remain trapped inside the system.
  • During Servicing: Another source of air in the cooling system is a human error during servicing. For instance, when the system isn’t appropriately bled, or coolant is incorrectly filled into the reservoir, air will get trapped and remain in the cooling system.

Being mindful of the above reasons will help prevent air from entering your car’s cooling system.

How Do You Keep Bubbles Out Of Your Car’s Cooling System?

Prevention is always better than the cure, as they say. That’s certainly true when it comes to bubbles in your car’s cooling system.

Here are 5 ways you can prevent air bubbles from getting into your car’s cooling system.

#1 Top-Up Or Change Coolant Regularly

Coolant is the lifeblood of the car’s cooling system. It’s also one of the many fluids in your vehicle that must be topped up regularly and changed when necessary.

When the coolant in your system is left for too long, plenty of its moisture will evaporate. But, unfortunately, that makes the remaining coolant incredibly thick and unable to displace any air inside the system.

In simpler terms, dried-out coolant leaves plenty of room for air to enter the system’s lines and get trapped inside.

You can prevent this by topping up coolant regularly to ensure little room for air to enter the system. Besides that, the old coolant should be drained out and replaced with fresh fluids instead

#2 Bleed Air After Pouring Coolant

In the previous section, you read that air bubbles get trapped in the cooling system after servicing. That’s quite normal as the reservoir is opened to refill with coolant.

The key preventive step here is to bleed the air out of the system after pouring coolant in. Preventing that is pretty straightforward.

After you pour fresh coolant into the reservoir, keep the radiator cap off while you run the engine. Let that continue for at least 15 minutes so any air trapped inside the system will escape through the opening.

You can replace the radiator cap after that time passes, as the system will be air-free.


Always be careful with hot engines, especially when removing the radiator cap. Because when the engine is hot and the coolant starts boiling, it can spray out, seriously burning you.

#3 Replace Faulty Thermostat

The thermostat is a critical component of the cooling system. It’s designed to ensure coolant flows at the correct times, particularly when a specific temperature is reached.

Unfortunately, a faulty thermostat will restrict coolant from flowing correctly. That will lead to the coolant boiling and creating air bubbles directly inside the cooling system.

Replacing the thermostat prevents that from happening by correctly regulating coolant flow. Of course, you must also bleed out any retained air after replacing that thermostat.

#4 Flush Reservoir And Radiator

Old coolant causes many different problems for the car’s cooling system. The older it gets, the more it becomes saturated with grime, dirt, and other impurities. Those things quickly clog the cooling system, indirectly causing coolant to boil and trapping air inside.

So, occasionally flushing the reservoir and radiator will clean the system and prevent that from happening.

It’s an excellent idea to flush the radiator and reservoir once every 5 years or after driving 100,000 miles.

#5 Regular Inspections

Steps #1 to #4 are excellent for preventing air bubbles from getting into your car’s cooling system. However, they’ll only happen if you notice those cooling system problems early enough to solve them quickly.

That’s why the #5 and the most essential way to prevent air bubbles from getting into your car’s cooling system is to inspect it regularly.

Regular inspections will ensure you catch leaks while they’re small or notice when the coolant starts to get thick or dirty.

Typically, inspecting the cooling system each time you get an oil change or perform other regular maintenance tasks is an excellent idea.

However, if it’s something that you’re particularly concerned about, you can also perform inspections more regularly.

What Happens If Air Bubbles Get Into The Cooling System?

Air bubbles are not to be taken lightly regarding your vehicle’s cooling system. They can cause significant issues in the long run, including:

  • Overheating engine: Firstly, remember that the cooling system is crucial to keep your car engine within safe temperatures. Unfortunately, air bubbles prevent the cooling system from functioning correctly, quickly leading to an overheating engine.
  • Steam from radiator: Aside from an overheating engine, the cooling system will become too hot to operate safely. Bubbles and overheating will cause steam to build up in the radiator and spew through leaks or a radiator cap blown off.
  • Thick or burnt radiator fluid: The many problems caused by air bubbles in a cooling system will cause the coolant or radiator fluid to become excessively thick as moisture evaporators. That will cause the system to clog and the fluid itself to burn.

As you can see, a few bubbles in the cooling system aren’t too bad. But the problem will gradually worsen if left untreated.

Thankfully, those problems can be prevented by keeping your car’s cooling system filled with enough coolant and free from any air bubbles.

Final Thoughts

Car owners have plenty to worry about to keep their vehicles in their best shape. But, unfortunately, the cooling system is an unsung hero that’s easy to overlook for many people.

Still, you should be mindful of yours, especially when it comes to keeping air bubbles out. The most minor air bubbles can accumulate and cause problems for the system and other parts in the engine bay.

A healthy cooling system keeps everything within safe operating temperatures so you can get the best performance from your vehicle.

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