Air in Cooling Systems (Causes, Symptoms, and Fixes)

Air in Cooling System

Air is an important aspect of a car’s system as it aids combustion, allows more power delivery, and ensures better fuel economy for your car. However, no matter how important air is to a car, having air in your cooling system is not good.

Air in cooling systems can lead to a lot of damage in your vehicle; your car’s engine will overheat, and at some point, it will damage your engine.

Air in the cooling system can also result in an airlock, making it impossible for the coolant to circulate properly through your engine. As a driver, you must learn to figure out if air is in your cooling system and possible ways of getting it out of your cooling system.

Here's a detailed guide on air in cooling systems, how to prevent it, and quick solutions when it happens.

How Do I Know If I Have Air Trapped in My Cooling System?

You can know if air is trapped in your cooling system in many ways. Understanding these common symptoms makes it easy for you to spot trapped air and rectify the situation before things become complicated.

Here are common symptoms of air in the cooling system:

1.  Overheating

One of the major things that having air in the cooling system will do to your vehicle is that you will experience an airlock. Air in the cooling system will introduce air bubbles, preventing proper coolant circulation around the car’s engine.

This is because air is not as good a heat conductor as water. Hence some passages in the engine will be filled with air, and when coolant is prevented from circulating through the engine, the engine will overheat.

The engine temperature can rise so high that you will notice heat loss in the cabin, especially during winter. If you notice something like this, you should check for any leakage in your air system.

2. Reduced Efficiency and Performance

With air in your cooling system, engine performance is reduced, affecting your gas mileage and power delivery across different internal components of your car’s engine. There are quite a lot of issues that can cause your vehicle to have reduced efficiency and performance, but you can also check if there’s air in your cooling system.

3. Poor Heater Performance

Air in a coolant system can cause poor heater performance because air pockets can form in the coolant system. Aside from causing overheating and engine damage, the air can accumulate at high points of the cooling circuit, making it impossible for air to circulate normally.

Because air is much lighter than antifreeze and poor circulation occurs, heater performance is affected.

The cabin heater's operation is disrupted, which can destroy engine operation. If you, for any reason, notice abnormal conditions in your heater or the presence of cold air at some points, then it is obvious that there is air in the cooling system.

4. Burning Smell

When you have air in your coolant system, there will always be overheating or engine damage which you can identify from the burning smell in your engine bay.

Overheating from air in the cooling system can cause the coolant to boil and create steam. This steam can then escape from the coolant system and create a burning smell.

Suppose you are experiencing a burning smell from your vehicle's engine compartment. In that case, having your vehicle inspected by a qualified mechanic to confirm if there is air in your cooling system is important.

How Does Air Get Into Your Cooling System?

It is common to hear drivers complain about how air enters their cooling system. But how does air actually make its way to your cooling system?

Here is a list of reasons why air is getting into your cooling system.

1. Leakages

Leakages remain one of the major reasons why air is getting into your cooling system. When there are leakages in the radiator hose, coolant will escape, and air will find its way into the cooling system.

This usually happens when there’s a crack in the hose, and the driver decides to ignore it because it doesn’t pose a major threat to his safety at the point of discovery.

2. Low Coolant Levels or Bad Coolant

Just as related to leakages, air will find its way into your cooling system if the coolant levels are low. Fluid has a consistent burn-up as the coolant is reducing or getting old.

This will lead to loss of viscosity, and if you continue driving your car in this condition, air bubbles will form and start getting into the cooling lines and eventually to the engine.

3. Blown Head Gasket

A blown head gasket remains one of the major reasons why air gets into the cooling system. When the head gasket is blown, air bubbles are formed and forced into the cooling system through the combustion cylinder.

4. Improper System Flushing

If the cooling system is flushed improperly, there’s a high chance that air pockets will be left. These pockets will eventually get into the cooling system.

What Happens If You Don't Bleed Air Out of a Cooling System?

Not bleeding air out of your car’s cooling system can pose many dangers to the vehicle.

Here’s a list of things that can happen to your car if you don’t bleed air out of the cooling system:

  • Engine overheating.
  • Reduced engine power and efficiency.
  • Low coolant levels from unrepaired leaks and cracks.
  • Temperature gauge will continue running hot.
  • Increased emissions.

How To Remove Air in Cooling System

There are different ways of removing air from your cooling system. You’ll need to choose the steps that match the design of your cooling system and capture the sets of tools that you have with you.

After removing air from your cooling system, don’t forget to fix any leaks that may have occurred. This will prevent the problem from happening again. You can also decide to check and replace the head gasket if any fault is detected.

The easiest way of removing air in a car's cooling system is by using the bleed point/bleed screw. Most vehicles have bleed points installed in the cooling system. All you have to do is to open the valve and let out the air. After removing the air, don’t forget to close the valve.

Top up your coolant level to the specified point as instructed by the manufacturer, start your car’s engine, and allow it to steam for some minutes. You can decide to raise the engine’s RPM to 3,000 RPM and allow the engine to run idle.

You can also remove air from your cooling system with the radiator cap. Open the radiator cap and fill up the coolant to the specified point as the manufacturer requires. After refilling, start the car’s engine and let it idle for at least 15 to 30 minutes.

You must ensure that your radiator cap is perfectly closed while you do this. After idling, let the car’s engine settle, then you can turn the bleed screw a few turns counterclockwise. Don’t remove the bleed screw completely, just enough to let out some coolant.

You can put a pan beneath the engine to collect the coolant that flows out. As the coolant comes out, you should notice some bubbles in them, especially if there’s air in your cooling system.

Continue the process until all air is out. Wait for the engine to cool down, and then you can top up the coolant to replace the ones that leaked out.

If your car doesn’t have a bleed screw, you can decide to mix your coolant with distilled water and fill it through the radiator. Turn on your engine and let your car steam. After the proper flow of the coolant, the air will be automatically purged from the system.

To stay safer, you should seek professional guidance in removing air from your car’s cooling system. This will also ensure that the root cause is also free.

How To Prevent Air From Getting Into Your Cooling System

Regular inspection is one way to prevent air from getting into your cooling system. Always check your cooling system for increased temperature, overheating, or even leaks.

Always ensure that you have fresh coolant in the radiator when necessary, and don’t forget to bleed out any air when necessary. Confirm that all connection points are properly sealed and that the coolant is properly circulated across all lines.

How Long Does It Take the Air To Get Out of a Cooling System?

Taking air from your car's cooling system should take roughly 15 to 30 minutes. However, you must understand that you might need another 15 or 20 minutes to heat up your car’s engine and idle it before everything is set for proper usage again.

What Does Air in the Cooling System Sound Like?

Air in the cooling system makes a gurgling sound. Most times, you might find it hard to figure out. The gurgling sound usually comes from the heater, and this is because of the air bubbles that are trapped in the cooling system.

Why Does Air in the Cooling System Cause Overheating?

Air in the cooling system causes overheating because when air gets into the cooling system, the air pockets fill different channels and block them. This causes an increase in temperature, hence the overheating.


Air in cooling is not an unrepairable issue. While it is true that you can easily bleed air out of the cooling system, you should locate the source and seal whatever damage that has been done.

This will get the air out of the cooling system and prevent it from happening again.