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How long does it take to get air bubbles out of a coolant system?

For most passenger cars, purging air from the cooling system generally takes about 15 minutes to an hour, depending on the vehicle and how stubborn the air pockets are. In many straightforward cases, a careful bleed runs 15–30 minutes, while more complex systems or stubborn pockets can stretch toward 45–60 minutes or longer. Some modern vehicles with sealed or electronically controlled cooling loops may require specialized procedures or professional service.

Air in the coolant can cause overheating, lose heater performance, and lead to long-term engine damage if not cleared. Bleeding involves venting air at bleed points, ensuring the heater core and radiator are filled, and verifying the system remains properly topped up. The following sections outline the factors that influence timing, a practical step-by-step bleeding guide, and typical timelines by engine type.

What influences how long it takes

Several factors determine the speed of a successful bleed. These include the design of the cooling system (how many bleed points it has and where they are located), whether the heater core and radiator are being vented, the position of the thermostat, the type of water pump (mechanical vs. electric), and whether the system was drained completely or only partially. Ambient temperature, driving conditions after bleeding, and any leaks or damaged hoses can also extend the process.

Bleeding the cooling system: a step-by-step guide

Before listing the steps, note that you should work safely and patiently. Always allow the engine to cool before opening the radiator cap or any bleed screws, use the correct coolant, and follow your vehicle manufacturer's guidelines. If you’re unsure, consult a repair manual for your exact make and model.

Safety and setup: Park on a level surface, engage the parking brake, and wear eye protection. If your vehicle has a radiator cap, plan to loosen it only when the system is cool; have a spill tray ready for any coolant that may escape.

Fill the system and locate bleed points: Fill the reservoir and/or radiator to the indicated level. Locate any bleed screws or valves near the radiator, thermostat housing, or water pump housing as described in your manual.

Set the heater to hot and run the engine: Start the engine and set the heater to the hottest setting. With the cap loosened or the bleed screws opened slightly, run the engine and bring it to operating temperature so the thermostat opens and coolant circulates.

Vent air and top off: As air is purged, coolant may bubble or spit from bleed screws. Open the bleed screws slightly to vent air until a steady stream of coolant (no air) flows, then close the screws. Keep the reservoir topped to the recommended level.

Cycle and check: For systems with multiple bleed points, repeat the venting process at each point. Gently squeeze hoses to help dislodge trapped air. After the engine reaches operating temperature and the coolant circulates steadily, turn off the engine and let it cool, then recheck and top off as needed.

In practice, many people complete the bleeding process in a single session, but some vehicles require a second pass or a short drive to ensure the thermostat opens and any lingering pockets are purged. If you notice persistent overheating, a heater that won’t get hot, foamy coolant, or continual coolant loss, stop and seek professional service to avoid engine damage.

Estimated timelines by engine type

Times below are general guidelines for typical bleed procedures after a coolant change or a coolant-related repair. Real-world results vary based on vehicle design and condition.

Simple four-cylinder engines (common passenger cars): typically 15–30 minutes to complete a bleed if following standard steps and no leaks are present.

Six- and eight-cylinder engines or those with multiple heater-core bleed points: roughly 30–60 minutes; may require a second pass or a specialized procedure to purge all pockets.

Modern engines with electric water pumps or sealed/canister-style cooling loops: about 20–60 minutes, depending on how easily air clears and whether the system can be bled through standard points or requires dealer tools.

Diesel engines and motorcycles: commonly 15–45 minutes for straightforward bleeding, with longer times if air pockets are stubborn or the system has been drained extensively.

Most drivers will complete the process in under an hour, but complex or high-performance applications can take longer. After a successful bleed, you may still need to drive the vehicle a short distance to reach optimal thermostat operation and to ensure the temperature gauge stays steady.

Signs there is still air in the cooling system

Be aware of indicators that air is still present after a bleed attempt. These symptoms suggest you should recheck the system or consult a professional:

Persistent or rising engine temperature after a bleed attempts

Heater output remains cool or only lukewarm

Foamy or discolored coolant in the reservoir

Visible coolant bubbling from the reservoir or near bleed points

Leaks around hoses, fittings, or the radiator cap

If any of these signs appear, stop driving the vehicle if overheating occurs and have the cooling system inspected for leaks, failed water pump, or clogged passages.

Summary

Air removal from a cooling system is a common maintenance task with a typical time frame of 15–60 minutes, depending on vehicle design and how aggressively air pockets are purged. A careful, methodical bleed—focusing on heater core and bleed points, plus topping off coolant and verifying operation—yields the best results. For stubborn systems or modern vehicles with advanced cooling loops, professional procedures may be necessary to ensure reliable cooling and heater performance.

Do air bubbles in coolant go away?

No, air bubbles in a cooling system don't always go away on their own and often need to be manually removed, a process called bleeding, to prevent engine overheating and other issues. Some newer vehicles can self-bleed over time, but many require a manual process like using a special funnel or a bleeder valve, which can take 10-15 minutes or longer. If the bubbling is constant and persistent, it could indicate a more serious problem like a blown head gasket.

This video explains how to manually bleed air from a car's cooling system: 53sCashedOutCarsYouTube · Sep 23, 2020
How to remove air bubbles

Use a spill-free funnel: Attach a funnel that fits into the radiator or reservoir cap. Fill the funnel with coolant and start the engine.
Use a bleeder valve: Some systems have a small bleeder screw on the thermostat housing. Open this valve to let air escape, while the funnel keeps the coolant level topped off.
Turn on the heater: Set your car's heater to its highest temperature and the fan speed to low to open the heater core and help air escape.
Let it run: Allow the engine to idle for 10-15 minutes until the thermostat opens and the bubbles stop rising through the funnel.
Monitor coolant level: Top off the funnel with coolant as needed while the engine is running.
Finish the process: After the bubbles stop, turn off the engine. Squeeze the top radiator hose, then remove the funnel and cap, and top off the fluid one last time before replacing the cap.

Signs of a problem

Constant bubbling: If you see a steady stream of bubbles, especially at idle, this could be a sign of exhaust gases entering the cooling system from a faulty head gasket.
Overheating: A system with air pockets is less efficient at cooling the engine, which can lead to overheating.
Poor heat from the vents: Air trapped in the heater core can prevent the cabin from getting warm air.

If you suspect a blown head gasket or are uncomfortable performing a manual bleed, it is best to take your vehicle to a professional mechanic for diagnosis and repair.

How do I get trapped air out of my coolant system?

To get air out of a coolant system, raise the front of the car, turn the heater to its highest setting, and then slowly fill the radiator with coolant while the engine is running. Allow the engine to reach operating temperature to open the thermostat and circulate the coolant, which will help push out trapped air bubbles. You can also squeeze the radiator hoses to help dislodge air pockets and continue to top off the coolant as needed until no more bubbles emerge.

Step 1: Prepare the car

Park the car on an incline or use a jack to raise the front end to help air move towards the highest point (the radiator cap).
Turn the vehicle's heater to the highest temperature and fan speed.
Remove the radiator cap slowly and attach a funnel to the radiator neck to prevent spills.
Begin to add coolant to the funnel, but don't fill it completely yet.

This video demonstrates how to prepare your car and a funnel for bleeding the cooling system: 58sGearheadbryanYouTube · Mar 23, 2025
Step 2: Bleed the system

Start the engine and let it idle.
As the engine warms up, the thermostat will open, and the coolant will begin to circulate, pushing air out through the funnel.
Monitor the funnel and top it off with coolant as the level drops, keeping the funnel from emptying completely.
Gently squeeze the upper and lower radiator hoses to help dislodge trapped air bubbles.
Once no more air bubbles are seen coming out of the funnel, and the heater is blowing hot air, the system is likely bled.

This video shows the process of bleeding air from the cooling system while the engine is running: 57sChrys GainesYouTube · Feb 2, 2023
Step 3: Finish the process

With the engine still running, carefully remove the funnel, using a rag or a plug to prevent spills.
Top off the coolant in the overflow reservoir to the "full" line if necessary.
Turn off the engine and let it cool down before fully replacing the radiator cap.
After the engine has completely cooled, check the coolant level one last time and top it off if needed.

How long does it take to get air out of a coolant system?

It takes about 15 to 30 minutes of idling and revving to bleed most of the air from a coolant system, but it can take up to a few days of driving and topping off to get all the air out. The process involves running the engine with the radiator cap off (or using a bleeder valve) and the heater on high, allowing air bubbles to escape. You'll know you're close when bubbling and gurgling stops, but you should still monitor your temperature gauge and top off the coolant as needed for a couple of days after the initial bleeding.
The bleeding process

Prepare the vehicle: Park the car on an incline with the front end higher to help air rise to the radiator cap. Ensure the engine is cool before starting.
Open the radiator cap and turn on the heater: Once the engine is running and has been warmed up, turn your vehicle's heater to the highest setting.
Watch and wait: Leave the radiator cap off and let the engine run. You will see the coolant level drop as air escapes and hear gurgling. Continue to fill the radiator with coolant as the level drops.
Rev the engine: Occasionally rev the engine to about 1000-3000 RPM to help push air out of the system and dislodge any trapped bubbles.
Check the temperature: Monitor the temperature gauge to ensure it remains in the normal range. You may need to repeat the process until the bubbling and gurgling stops.

After the initial bleeding

Top off the overflow reservoir: Fill the overflow reservoir to the "cold" fill line with the correct coolant mix.
Monitor for a few days: Keep an eye on the coolant level in the reservoir for a couple of days and top it off as needed.
Re-check and top off: After a few days of driving, when the engine is cool, check the level in both the radiator and overflow reservoir and top them off if necessary.

Will air work itself out of a cooling system?

No, air will not automatically work its way out of most cooling systems; you must manually "burp" or bleed the system to remove trapped air pockets, especially after a coolant flush or repair. While small bubbles may eventually dissipate, large air pockets can cause serious engine overheating and damage by preventing coolant from reaching key components.

Why air gets trapped and why it's a problem

Air can get into the system when the cooling system is opened for maintenance.
It can get trapped in high points of the system, like the heater core, preventing proper circulation.
These pockets create areas of the engine that are not cooled, which can lead to overheating and damage like warped cylinder heads or a blown head gasket.

How to manually bleed the system

Use a special funnel: A spill-free funnel that fits into the radiator or reservoir opening can make the process easier. Fill the funnel with coolant.
Raise the front of the vehicle: Jacking up the front of the car can help trapped air move to the highest point, allowing it to escape.
Turn the heater on: Set your car's heater to the highest heat setting and the fan to full blast. This opens the heater core, creating a path for air to escape.
Start the engine: Once the engine is running, monitor the coolant level in the funnel and top it off as needed.
Squeeze hoses and rev the engine: Gently squeezing the radiator hoses can help dislodge bubbles. You can also rev the engine, which can help move air through the system.
Continue until no more bubbles appear: Keep the engine running until the cooling fans cycle on and off twice, indicating proper circulation. You should be able to tell all the air is out when no more bubbles come out of the funnel and the coolant level is stable.

You can watch this video for a demonstration of the process of bleeding a coolant system: 48sChrys GainesYouTube · Feb 2, 2023

Kevin Bennett

Company Owner

Kevin Bennet is the founder and owner of Kevin's Autos, a leading automotive service provider in Australia. With a deep commitment to customer satisfaction and years of industry expertise, Kevin uses his blog to answer the most common questions posed by his customers. From maintenance tips to troubleshooting advice, Kevin's articles are designed to empower drivers with the knowledge they need to keep their vehicles running smoothly and safely.