How do you get air out of a Subaru cooling system?

Air in a Subaru cooling system is purged by filling the system and then venting any trapped air through bleed points while the engine circulates coolant with the heater on, until the coolant level remains steady and the engine maintains normal temperatures.

Why air gets trapped and why it matters

Air pockets can form when the cooling system is opened, refilled, or after repairs. Air does not circulate like coolant, which can lead to overheating, hot spots, and, in extreme cases, head gasket damage. Subarus, particularly some 2.5L engines, are known to require careful bleeding to prevent these issues.

Preparation and safety

Before you begin, ensure the vehicle is on level ground and the engine is completely cool. Use the correct coolant specification ( Subaru-approved or equivalent), wear eye protection and gloves, and never remove the radiator cap while the engine is hot. If you’re unsure about your model’s bleed points, consult the owner's manual or a qualified technician.

Step-by-step bleed procedure

Follow these steps to purge air from the cooling system. The exact steps can vary by model, so consult your owner's manual for bleeder valve locations specific to your engine.

1. Park on level ground and let the engine cool completely. Wear protective gear.


2. With the engine cold, remove the radiator cap (if present) and the expansion/overflow tank cap to vent pressure.


3. Slowly fill the radiator and expansion tank with the correct coolant until coolant begins to flow and the levels approach the recommended marks.


4. If your model has a bleed screw on the thermostat housing or a dedicated bleed port, loosen it slightly to allow air to escape. You should see air bubbles and coolant begin to flow.


5. Reinstall the radiator cap loosely (or keep the expansion tank cap off as needed) and start the engine. Set the heater to HOT with the blower on high to circulate coolant through the heater core and purge air.


6. Let the engine run until it reaches its normal operating temperature and the thermostat opens. Watch the expansion tank; as air is purged, the level may fluctuate. Add coolant as necessary to keep the level near the MAX line.


7. If you opened a bleed screw, retighten it once a steady stream of coolant flows with no air pockets. Recheck and secure both caps.


8. Turn off the engine and allow it to cool, then recheck coolant levels and top off if needed before a test drive.

The goal is a steady, bubble-free flow of coolant and stable levels in the expansion tank, indicating the system is properly purged.

Model-specific notes

Bleed procedures can vary between engine generations. Some Subarus use a dedicated bleed screw on the thermostat housing, others rely on heater-core bleeding and careful filling. If your model lacks an obvious bleed screw, rely on heating the system through the heater and monitoring the expansion tank while the engine runs. Always refer to your specific model’s service manual for exact locations and procedures.

Common bleed locations you may encounter

Locations differ by model, but these are among the points technicians check when purging air from Subaru engines:

• Thermostat housing bleed screw (a small screw on or near the housing).


• Radiator neck bleed port or a dedicated vent near the fill neck.


• Expansion tank/overflow reservoir and associated hoses (to purge air via the reservoir).


• Heater core path through the heater hoses when the heater is set to HOT.

Not every Subaru uses all of these points. If you can’t locate a bleed screw or meaningful vent, consult the owner’s manual or a Subaru service professional for model-specific guidance.

Safety reminders and potential issues

Never remove the radiator cap while the engine is hot. Use caution to avoid scalding, and wear protective gear. If overheating persists after bleeding, or you notice white smoke, a sweet smell, or milky oil, stop and seek professional help, as these can indicate more serious cooling system problems or head gasket issues.

Summary

Bleeding air from a Subaru cooling system focuses on filling the system, venting air via bleed points (if present), and circulating coolant with the heater on until you achieve a stable, bubble-free coolant level. Always follow the specific steps for your model from the owner's manual, and consider professional service if air pockets persist or overheating recurs.

How do I get trapped air out of my cooling 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 to properly bleed air out of a cooling system?

Hot setting. But at a low speed. There we go and now just let it run now as you do this you're going to see the coolant. Level rise up.

How to get air out of a Subaru cooling system?

To burp a Subaru cooling system, fill the system with a coolant mixture, then run the engine with the radiator cap off and the heater on maximum heat. Use a no-spill funnel kit for easier filling and to prevent overflow, and squeeze the radiator hoses to help dislodge air bubbles. Allow the engine to reach operating temperature and rev it to force out any remaining air bubbles until no more bubbles appear in the funnel.
 
Step 1: Prepare the system

• With the engine cold, attach a no-spill funnel kit to the coolant reservoir or radiator cap opening. 
• Fill the funnel with the correct coolant mixture. 
• Turn the vehicle's heater to the highest heat setting and the fan speed to a low setting. 
• If your model has a radiator cap, you may need to jack up the front of the car to make the highest point in the system accessible for bleeding. 

Step 2: Run the engine and bleed the air

• Start the engine and let it idle. 
• As the engine warms up, the coolant level in the funnel will drop and you will see air bubbles rise to the surface. 
• Continue to add coolant to the funnel as needed to keep it full and prevent air from being sucked back into the system. 
• Squeeze the upper and lower radiator hoses to help dislodge trapped air. 

Step 3: Finalize the process

• Allow the engine to run until it reaches its operating temperature, which is indicated by the fans cycling on at least once or twice and the coolant temperature gauge showing a normal reading.
• Rev the engine to 3,0003 comma 0003,000 to 4,0004 comma 0004,000 RPM for a few minutes to force out any deeper air pockets.
• Continue to run the engine until no more air bubbles are seen in the funnel for at least five minutes.
• Turn off the engine and allow it to cool down before carefully removing the funnel.
• Remove the funnel, top off the coolant in the reservoir to the "full" line if necessary, and replace the radiator cap.
• Monitor the coolant level in the overflow tank for the next week, as it may need to be topped off as the system fully settles. 

How to burp a radiator on a Subaru?

Rev the engine between 2500 to 4000 rpm off and on for 5 minutes, this should allow the water pump to force air out of the system.