What Causes Air Bubbles in Radiator? Symptoms & Fix

Air bubbles in a car’s radiator come with severe consequences if not checked and eliminated. You may be wondering, “What causes air bubbles in radiator?” There’s no one specific reason, as several causes have been unveiled in this article.

The encumbrance that comes with engine damage and the financial implications results from leaving air bubbles in your car’s cooling system.

If you’re experiencing engine overheating and other related challenges possibly damaging your vehicle’s engine, you may want to spare some time to digest this post.

air bubbles in radiator

What Causes Air Bubbles in Radiator?

There is no one-fits-all reason you have air bubbles in your car’s radiator, as several issues may be responsible. Nevertheless, the following are some common causes of air bubbles in coolant system like coolant leaking, low coolant level, faulty radiator cap, damaged head gasket or blocked radiator fins etc.


A leak in the cooling system can allow air to enter the radiator, leading to bubbles in coolant reservoir. Leaks can occur in several different places, such as the radiator itself, hoses, water pump, or engine block.

A visual inspection of the system can help identify leaks, but a pressure test may be needed to pinpoint the exact location.

Low coolant levels 

If the coolant level in the radiator is low, air can find its way into the system and cause bubbles. Therefore, ensure always to check coolant levels and top it off regularly.

Failed radiator cap 

The radiator cap is essential in regulating pressure in the cooling system. If the cap is damaged or worn out, it may not seal properly. It can allow air to enter the system.

Clogged radiator 

A build-up of debris or sediment in the radiator can impede the flow of coolant and cause air bubbles in a radiator. Flushing the radiator periodically can help prevent this issue.

Head gasket failure 

A blown head gasket can allow air to enter the cooling system, leading to bubbles in the radiator. This is a more serious issue that requires professional attention.

Overall,  air bubbles in coolant reservoir can be caused by a various factors. Regular maintenance, including checking coolant levels and inspecting the cooling system for leaks can help prevent this issue from occurring.

If air bubbles are present, it’s important to identify and address the underlying cause to avoid engine damage.

What are Signs of Air in Coolant System?

Air bubbles in a radiator can cause various symptoms that can lead to engine damage if not addressed promptly. Some common symptoms of air bubbles in a car’s radiator include the following.


Overheating is one of the most common symptoms of air bubbles in a car’s radiator. When air bubbles enter the cooling system, they can hinder the coolant from flowing properly through the engine, which can cause the engine to overheat.

Loss of coolant 

Another symptom of air in the radiator is a loss of coolant. When air bubbles enter the cooling system, they can displace the coolant, decreasing the amount of coolant in the system.

Fluctuating temperature gauge 

The temperature gauge on the dashboard of a car can provide a clue that there are air bubbles in the radiator.

If the temperature gauge fluctuates between normal and high, it could be a sign that air bubbles are preventing the coolant from flowing properly.

Gurgling sounds 

When air bubbles enter the cooling system, they can create gurgling or bubbling sounds as the coolant tries to circulate the engine. These sounds can often be heard from the radiator or the coolant reservoir.

Coolant leaks 

Air bubbles in the radiator can cause coolant to leak out of the system. If you usually notice a puddle of coolant under your car or a low coolant level, it could indicate air bubbles in the radiator.

If you notice any of these symptoms, having your car’s cooling system checked by a professional auto mechanic as soon as possible is important to prevent engine damage.

How do I get rid of Air Bubbles in my Radiator?

Air bubbles in the radiator can lead to overheating and potential damage to your car’s engine. Fortunately, there are several methods of getting air out of radiator and ensuring that your car’s cooling system functions properly.

If you have air bubbles in your car’s radiator, here are the steps to follow to remove the bubbles from the cooling system.

Get Rid of Air in Coolant YouTube

Step 1: Turn off the car’s engine

Firstly, turn off your car and let the engine cool down completely before attempting to remove any cooling system components.

Step 2: Locate the radiator and open the cap 

Locate the radiator. If your car has a pressurized coolant recovery or overflow tank, locate it as well. Open the radiator cap or the coolant recovery tank cap, depending on which your car has. 

Be careful when opening the cap; the coolant could be hot and under pressure. Use a towel or rag to protect your hands, and slowly twist the cap to release pressure.

Step 3: Start the car and let it idle

Start the car and let the engine idle for several minutes, allowing the coolant to circulate. Turn on the heat in the car to the maximum temperature setting. This will help circulate the coolant and move any air bubbles out of the system.

Watch the coolant level in the radiator or coolant recovery tank. As the engine runs, you should see the level of the coolant drop as it circulates through the system.

Step 4: Add more coolant 

Now is the time to add coolant as necessary to maintain the proper level in the radiator or coolant recovery tank. 

Then, keep watching the coolant level and checking for air bubbles in the system. You may need to perform the exercise a few times until all the air bubbles have been removed.

Step 5: Reinstall the radiator cap 

Once you’re satisfied that all air bubbles have been eliminated, reinstall the radiator cap or coolant recovery tank cap, and ensure it’s securely tightened.

Step 6: Go for a test drive

Take the vehicle for a short test drive to ensure the engine runs smoothly and the temperature gauge reads normally.

Suppose you find that air bubbles continue to appear in the coolant system after following the steps above. In that case, you may need to seek the help of a professional auto mechanic, as there could be a more complicated problem with the cooling system.


Several causes have been outlined in this article if you were wondering, ”What causes air bubbles in radiator?” So, if you suspect air bubbles in your car’s cooling system, ensure to verify the exact cause of the problem.

Meanwhile, air bubbles in your car’s radiator can cause serious damage to the engine in the long run. Therefore, it is crucial to take preventive measures once you notice engine overheating, low coolant level, temperature gauge instability, etc.

Resolving any issues relating to air in coolant is relatively simple to handle. However, ensure to consult a professional auto mechanic in critical cases.


Mr. Shafiqule Islam is a graduated Mechanical Engineer and has more than 15 years experience of repairing and maintenance of different brand vehicles like Toyota, Mitsubishi, Ford, Mercedes, BMW etc. He is also giving training to Mechanics. He has started writing to share his practical knowledge to Vehicle Owners, Drivers and Mechanics to keep their cars at best fit.

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