How to Bleed Your Cooling System

Bleeding Air From Cooling System

Removing air pockets or air bubbles from an engine is how you bleed your cooling system.  This process can be referred to as bleeding air, purging or burping a cooling system. Cooling system air pockets develop after performing any cooling system service, like a coolant flush, changing a water pump or a radiator repair.  Anytime you lose or remove antifreeze from your vehicle you have the potential of an air pocket forming.  Trapped air, stuck in your engine will prevent you from refilling the cooling system fully and can lead to overheating, engine damage and a breakdown.

Preventing Cooling System Air Pockets

To prevent a cooling system air pocket, you will need to refill your cooling system properly. Using a mixture of 50/50 antifreeze and water, add coolant until the system seems full. Leaving your radiator cap off, you should start your vehicle and turn your heater on high. Let the vehicle idle for about 15 minutes watching the fluid level.

As your vehicle heats up and starts to circulate you will see the coolant rise and fall a little, and you may see air bubbles being released as the thermostat starts to open. You are now purging your cooling system of air as the water pump begins to pump coolant through your system pushing air out. As you are running the vehicle, add coolant as the air is released, and the coolant level drops. Keep doing this until the heater is blowing hot air, all the air bubbles have stopped, and the fluid level stays full and no longer drops.

Some mechanics recommends jacking up the front of the vehicle and making sure the radiator is higher than the engine or putting the front of the vehicle on an incline to help burp the cooling system. We never did this at our shop and I do not think that doing this is necessary most of the time.

When you are filling the cooling system and warming up the vehicle, you will need to open any bleeder valves your vehicle may have and allow the trapped air to be released. Make sure you know if your system has any bleeder valves and where they are located. You will need to open them until all air is released, and until you see fluid coming out. If your cooling system has a bleeder valve it will be important to use it.

Cooling System Air Pocket Symptoms

The best thing you can do to protect yourself from an air pocket is to watch the gauge and double-check your coolant level after any work on your cooling system. Most air pockets will show themselves quickly, and it is key that you check your fluid right after any cooling system service. If you lose heat after any cooling system repair, you probably have an air pocket. Check your coolant level and top off your cooling system.

At our shop, we would always run a vehicle after any cooling system work and “burp” the cooling system of air. We would allow the thermostat to open and circulate the fluid throughout the system making sure the heater was working properly. We would then check and double-check all fluid levels, open any bleeder valves and make sure everything was topped off.

Remember, vehicles will not purge themselves and must be “burped”. To burp a cooling system the thermostat must be open, and the system must be hot and fluid pumping through it. Your heater must be on hot and venting hot air. All bleeder valves must be opened to release air from any high point in the cooling system and then shut securely. Finally, after any cooling system repair, right after driving the vehicle for the first time,  take a minute to check your vehicle and all fluid levels. If you are not comfortable with any of these procedures let your mechanic do this for you. Remember, always check your coolant level after any repair and make sure you bleed your cooling system properly, or you will overheat.

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