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How to Bleed Your Car's Cooling System

Updated on February 21, 2017
Air pockets in the cooling system may cause serious engine damage.
Air pockets in the cooling system may cause serious engine damage. | Source

You need to bleed the air out of the cooling system in your car. Air pockets — or hot spots — are dangerous; they can overheat, crack or warp any part of the engine where air is trapped.

Usually, replacing the coolant or servicing the cooling system in your vehicle can lead to hot spots in the system. But air may also enter the system through the coolant reservoir from time to time on some vehicle models.

A hot spot is nothing more than trapped pockets of air or bubbles inside cooling system passages that prevent coolant from carrying heat away from those areas, causing the engine to overheat and corrosion to start setting in.

To bleed the air out the cooling system you can follow one of three different methods, depending on whether your particular system comes with bleeding screws or not.

If you don't know whether your system comes with a bleeding screw(s), consult your car owner's manual, or check your vehicle service manual. You can buy a repair manual for your particular vehicle make and model in many auto parts stores or online. Still, you may find a copy of the manual in the reference section of your local public library.

Either way, read on. The descriptions provided here may help you determine the method to use in your particular car.

Wait for the engine to cool before bleeding the cooling system.
Wait for the engine to cool before bleeding the cooling system. | Source

How to Bleed a Cooling System Equipped with a Bleed Screw

The bleeding screw is usually located around the top of the engine. The most common place is right on the thermostat housing where the upper radiator hose connects to the engine. If you see an orphaned, single screw, your cooling system has a bleed screw — some systems come with more than one bleed screw, though. Check your car owner's manual or repair manual, if necessary.

Before you begin this procedure, make sure the engine and radiator are cool. If they are hot, wait an hour or more.

1. When ready, remove the radiator cap

2. If necessary, bring the coolant to the proper level by adding a 1-1 ratio mixture of distilled water and antifreeze. Fill the radiator up to the bottom rim of the radiator neck with the mixture.

3. Add coolant to the reservoir as well. Bring the coolant level to the "Cold" mark.

4. Replace the radiator cap.

5. Locate the bleed screw and place a pan on the floor to catch the coolant that will come out through the screw.

6. Start the engine and let it idle for about 20 minutes to bring the engine to operating temperature — when the engine has reached operating temperature, you'll feel the upper radiator hose getting hot.

Warning!

Don't remove a bleed screw while bleeding the cooling system or you may seriously burn yourself with hot coolant.

7. Once the engine has reached operating temperature, turn the coolant bleed screw one to two turns counterclockwise using a wrench of the correct size. But don't remove the screw off the thermostat housing or you'll have a stream of boiling coolant coming out of the valve. You can seriously burn your skin.

8. When you see a stream of coolant free of air bubbles flowing from under the screw, tighten the screw again.

9. Turn off the engine and wait for it to cool.

10. Add more new coolant to the radiator — up to the bottom of the radiator neck — and the reservoir, if necessary.

11. Test-drive your car and see if the temperature stays within the normal parameters. Otherwise, head over to the third section below "How to bleed a radiator using two jack stands."

12. Over the next few days, check the coolant reservoir from time to time to make sure it remains at the correct level.

Hot Pockets of Air in the System Can Cause Severe Damage
Engine overheating
Crack in engine
Warped spots in engine
Increased emissions
Some cooling systems don't have a bleeding screw.
Some cooling systems don't have a bleeding screw. | Source

How to Bleed a Cooling System That Doesn't Have a Bleed Screw

Systems without a bleed screw require a slightly different method to purge trapped air. First, make sure the engine and radiator are cool.

1. Remove the radiator cap.

2. Fill the radiator with a 1-1 ratio mixture of distilled water and antifreeze up to the bottom of the radiator neck. Mix only distilled water with the antifreeze.

3. Add coolant to the reservoir container to bring the level up to the "Cold" mark as well.

4. Leave the radiator cap off and start the engine.

5. Let the engine reach operating temperature. When the engine reaches operating temperature, you'll see through the radiator neck the coolant flowing. Also, the upper radiator hose will become hot.

6. Wait for a few seconds to allow coolant to flow. At this point, air has been purged from the system.

7. Turn off the engine and let it cool.

8. Then, add more coolant to the radiator if necessary, to bring the level up to the bottom of the radiator neck.

9. Squeeze the upper radiator hose to expel air after adding more coolant, and add more coolant if necessary.

10. Replace the radiator cap.

11. Start the engine and let it reach operating temperature.

12. Test drive you car and monitor the engine temperature (if the engine still overheats, use the next method to remove the remaining air form the cooling system).

13. Check for coolant leaks and then turn off the engine.

14. Monitor the coolant level on the reservoir over the next few days and add coolant as necessary.

How to Bleed a Cooling System Using Two Jack Stands

Some cooling systems are harder to bleed than others, even if they provide more than one bleeding valve. Try this method to purge the remaining air.

1. Park your vehicle on a level surface.

2. Make sure the engine and radiator are cool.

3. Use a floor jack to jack up the front of your vehicle so the radiator neck is at a higher level than the engine. Then, secure the vehicle with a jack stand on each side.

4. Block the rear wheels using a couple of wooden blocks.

5. Set the parking brake.

6. Remove the radiator cap and start the engine.

7. Wait until the engine has reached operating temperature.

8. When the engine reaches operating temperature, wait for a few seconds for the system to expel the air. Then turn off the engine.

9. When the engine cools, add coolant to the radiator to bring the coolant to the correct level. Squeeze the upper radiator hose to expel any trapped air.

10. Add coolant to the reservoir as well, if necessary.

11. Test-drive the vehicle.

Bleeding the cooling system requires a few simple steps. Still, you may need to try more than one method, besides the one recommended by your car manufacturer, to successfully bleed the cooling system. Follow either one of the previous methods, depending on your particular vehicle model, every time you need to replace the coolant or when adding coolant to the system between service intervals. This will help you get rid of hot spots, and the potential for serious engine damage.

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