Air Lock in Cooling System: Reasons and Common Ways to Fix

Airlock in the cooling system increases the risk of overheating. The cooling system cannot function optimally with trapped air pockets. It is advisable to bleed out the trapped air quickly to protect your car engine. This practical guide explains how the cooling system and the symptoms of an airlock in the system. The guide also outlines the causes of air pockets in the cooling system and different fixes.

Coolant circulation problems highlights

• Level of urgency:medium
• Commonreasons:bad coolant, air lock, thermostat issues
• DIY diagnostics:complicated
• DIY repair:impossible
• Price of repair:$250 - $650
• Time for repair:2 - 7 hours
• If ignored:fatal overheating and engine damage

How Does the Cooling System Work?

The cooling system has several parts that cool the engine and maintain the correct operating temperatures. The system has a thermostat, which is a temperature-sensitive valve that allows the coolant to flow when the engine is hot.

The water pump has an impeller that controls the coolant flow. The coolant flows through the engine block, absorbs the heat, and flows into the radiator. Air passes through the coils in the radiator to disperse the heat in the coolant.

The cool coolant flows through the radiator hose back to the water pump to start the cooling cycle again. Air trapped within the cooling system interrupts the coolant flow into the engine block.

Symptoms of Air Lock in the Cooling System

The air pockets in your car's cooling system will produce strange sounds and increase the overheating risks. A failing heater core and low coolant levels may also indicate an airlock in the cooling system.

1. Overheating

Your car will overheat when air is trapped in the cooling system. The temperature sensors report inaccurate readings because of the air bubbles. Consequently, the car system does not turn on the cooling system or fan.

Air bubbles in the thermostat interfere with its function. The valve will only open for the coolant to flow once the temperatures are extreme. A functional cooling system prevents temperature fluctuation.

Temperature fluctuations indicate cooling system issues, including airlock.

2. A Failing Heater

An airlock in the cooling system causes the car heater to malfunction. Heat does not flow through the vents when you switch on the heater. The air pockets prevent the hot coolant from flowing through the heater core.

3. Dashboard Sounds

You may hear a strange gushing sound coming from the dashboard when driving. The air within the system causes the coolant to make a weird noise when flowing through the heater core. The sounds may start when you switch on the engine.

4. Overheating after Repairs

Car parts require repairs and maintenance to maintain their optimal performance. The cooling system is complex to repair. The system may contain air pockets if your car overheats after repairing its parts.

5. Other Symptoms

Air bubbles may lead to reduced performance and leakage in the cooling system. You may notice that you are losing coolant too quickly, or the engine heat is irregular. You need clear the air pockets to protect the engine.

Common Reasons for Airlock in the Cooling System

If you notice one or more signs of air bubbles in the cooling system, you need to determine the cause. The process involves identifying the broken part of the system that allows air or gases from outside to flow into the system.

1. A Bad Radiator Cap

The radiator cap prevents coolant leaks and maintains the required pressure for the coolant to flow easily. A damaged or loose cap allows air into the system and reduces the fluid pressure.

2. A Blown Head Gasket

A blown head gasket leads to air bubbles in the radiator. A leaking gasket allows combustion gases from the cylinder engine into the coolant system. A radiator with trapped gases or air cannot efficiently lower the coolant's temperature.

3. Radiator Hose Leaks

When coolant leaks out of a broken radiator hose, it allows air from outside to flow into the system. Coolant leaks under a parked car indicate a leaking radiator hose.

4. Poor Flushing

Flushing the cooling system is necessary to remove air bubbles and other contaminants. However, improper flushing may introduce new airlock problems instead of pushing the air bubbles out.

If you choose to flush the system instead of involving a mechanic, ensure that you follow the proper procedures.

5. Improper Coolant Refill

The coolant level must be sufficient to regulate the engine temperature effectively. A bad refill when the coolant is low may form air pockets. You will incur an extra cost and the inconvenience of flushing the system again.

Why Should You Remove Air in the Cooling System?

Is driving a car with an airlock in the cooling system dangerous? Yes. The high temperatures due to reduced performance may lead to an overheating engine. You will incur high repair costs if the components fail due to overheating.

An overheating engine can cause cracks in the engine blown, a leaking head gasket, and a blown radiator cap. Other consequences are warped pistons and cylinders, poor engine performance, and reduced fuel economy.

How to Flush Air Out Of the Cooling System

The proper way to flush or bleed out air bubbles in the cooling system depends on your car model. The process is easy if your car has a bleeding screw or valve. We will also discuss alternative ways to drain the air without a bleeding valve.

The bleeding screw is located on top or in front of the radiator. Consult your car manual to determine if the car has a bleeding screw and its location. Opening the bleeding screw allows the trapped air to escape.

Flushing through the Radiator Cap

The method is applicable with and without a bleeding valve. Here is the procedure:

1. Prepare the coolant

The engine coolant consists of equal parts of antifreeze and water. You do not need to drain the system if the old coolant is clean. Instead, add a new coolant to bleed out the air bubbles.

Ensure that the coolant mixture is the same as the coolant in the system.

2. Add the coolant and start the engine

Remove the radiator cap and pour the coolant all the way to the top. Pour some of the coolant into the coolant reservoir. Close the radiator and turn off the engine for a few minutes.

The coolant will flow through the engine block, pushing the trapped air out. 

3. Switch off the engine

Turn off the engine and open the radiator cap. The air will flush through the radiator as the engine cools to its right temperature. The trapped air may release a gurgling sound as it escapes.

Check the temperature gauge as the air bleeds. The additional coolant in the radiator should cool the engine down to its average temperature or close.

4. Add coolant to the radiator

The coolant level will decrease after all the air bubbles escape. Your risk overheating problems if you leave the radiator half empty. Add more coolant to the maximum level mark.

Refill the overflow tank as well to ensure that all the trapped air has escaped from the system. You can also squeeze the radiator hose gently to push the air bubbles.

5. Close the radiator

Put the radiator cap back on and screw it tight. A loose cap will let the air back in again. In addition, consider replacing a worn-out or damaged cap. Order the right radiator cap from a reliable auto shop for your car model

6. Test drive

Testing a car after fixing the airlock is important to verify that the cooling system works. A short drive will show if the system cools down the engine and maintains the appropriate temperature effectively.

Flushing Using Jack Stands

Lifting your car with jack stands is an alternative method of draining trapped air. If you have been driving, park the car and turn off the engine. Wait until the engine and radiator cool down.

Use a floor jack to lift the car so the radiator's neck is above the engine. Use jack stands to secure both sides of the car and engage the parking brake.

Remove the radiator cap when the car is in this position and start the engine. Keep the engine running until it reaches the perfect temperature for the coolant to flow.

The process flushes the air pockets thoroughly. Turn off the engine when you are sure that all the air is drained. Squeeze the radiator hose a bit to bleed out any remaining bubbles.

Allow the engine to cool down before refilling the coolant level. Test-drive the car while checking for previous airlock symptoms. The cooling system should function optimally if the flushing process is effective.

Seek Professional Help

Seek a qualified mechanic's help if the airlock symptoms persist after attempting to flush out the air bubbles. The cooling system may have damaged parts that require repair or replacement.

Regular car service is advisable for the mechanic to inspect the system and solve issues quickly. You can also prevent overheating issues by cleaning the cooling system regularly and maintaining the required fluid levels.

Conclusion

Air trapped in the cooling system reduces the system's performance, increasing the risk of overheating. The common symptoms of airlock are a failing heater core, overheating while driving, strange dashboard sounds, and overheating after repairs. The parts prone to allowing air pockets into the cooling system include the radiator cap, head gasket, and radiator hose.

Ignoring the airlock symptoms is risky. You can bleed out the air bubbles with new coolant before your mechanic replaces any broken cooling system parts.