How to bleed a car radiator

Our safe DIY method to ‘burp’ the air out of your radiator

Watch our video to see us top up and burp a car radiator.

Read our guide below for even more detail.

Bleeding your radiator is the absolutely critical last step in topping it up. If you’re interested in learning how to safely and properly bleed your radiator by yourself, this will involve topping up the coolant correctly.

You should read our article about how to top up your car’s radiator coolant yourself first.

Of course, bleeding the radiator is actually a common solution for a host of seemingly unrelated problems, too. Say, for example, your RPMs constantly jump while your car’s idle. It might be worthwhile checking if the issue lies with trapped air inside your car’s cooling system.If this doesn’t resolve the issue, seek help from a qualified professional.

Learning how to bleed the air out of your radiator is a useful skill to learn. It is also fairly straightforward to understand.

What does it mean to bleed a car radiator?

Bleeding a car radiator means removing air pockets trapped within the cooling system.

Your car’s cooling system circulates coolant through the radiator and engine block to prevent overheating. Air pockets in the cooling system allow heat to build up causing extreme hot spots which can damage your engine.

Air can get into your radiator, especially if the coolant level is too low or if you’ve recently drained it. Bleeding your radiator is necessary to remove the air.

If, after reading these steps, you’re still not confident to tackle this yourself, you can always call our car radiator specialists to do it for you. We’ll gladly help you out and give your coolant system a thorough check as well.

How long does it take to bleed a radiator?

The radiator bleeding process takes a few minutes.

What you’ll need to do the task

• Coolant (correctly diluted and compatible with your existing coolant)
• A funnel (ideally a spill-proof radiator filling kit)
• A wrench the same size as your bleed valve (this is optional)

5 steps to bleed the air from your car radiator

1. Turn off the engine

Your engine needs to be completely cool before you begin. The last thing you want is to suffer burns from hot coolant.

2. Remove the radiator cap

The radiator cap is typically located at the top of the radiator. In most modern cars, this cap is situated at the highest point of the coolant system so air bubbles naturally accumulate there.

To remove the radiator cap, first wrap it with a thick rag and give it a half-turn anticlockwise. This will allow any residual pressure to escape.

Your radiator may have an overflow tank

Some vehicles have an overflow (also called expansion) tank connected to the radiator. If yours does, remove the cap from the overflow tank using the same method as above. If you have an overflow tank, you’ll be bleeding air from the tank rather than from the radiator directly.

3. Top up your coolant system

Place the funnel into the radiator filler neck or overflow tank. Use the correct adaptor to ensure a tight seal so the funnel is secure.

Slowly pour the coolant into the funnel. Pour with a steady, slow stream to avoid adding any air bubbles.

Keep pouring until the coolant level reaches the ‘full’ marker on the inside of the overflow tank or until it brims the radiator. Leave the funnel in place.

You can try squeezing the top radiator hose to expel any air trapped inside it.

You can use your bleed valve to ensure the engine cooling system is full

This is an optional step since a bleed valve is not included on all radiator types. It looks like a little screw sticking out of the radiator, but its location differs by make and model. You may be able to use your owner’s manual to locate your car’s bleed valve.

The purpose of the bleed valve is to bleed air and release pressure from the cooling system. 

To use the bleed valve, loosen it (but do not remove it completely) and then begin to top up your coolant. As the added coolant enters the system, you may hear air escaping from the valve. Then, coolant will start to sputter out of it. Keep topping up slowly.

When the coolant starts to pour out of the bleed valve in a steady stream, tighten the valve again. At this point, your system is full and has little or even no air in it.

4. Run your engine and burp the coolant

Clear away any tools or rags from around the engine, leaving the funnel in place and secure.Turn on your car’s engine and set the A/C to its hottest setting.

This will allow the coolant to cycle through the engine and entire cooling system while bringing any trapped air to the top.

Any air in your system should bubble up and ‘burp’ out of the funnel.

You will need to keep your engine running for a few minutes. Rev your engine to about 3,000 RPMs occasionally to help dislodge and push out any trapped air.

Keep a close eye on the coolant level in the funnel. It may rise, as coolant expands under heat and pressure, or it may drop as it cycles and air bubbles escape.

If your coolant level drops below full, top it up with more coolant and continue the burping process.

5. Shut off the engine and top upof the coolant

Your coolant level should stop fluctuating and even out. Once that happens, turn off the car engine and let it cool down completely.

Once your engine is cool, your coolant level might drop. Top it up taking care not to overfill.

Remove the funnel and replace the radiator cap.

Pro tip: If you’re using a professional radiator funnel kit, it should come with a funnel stop. You can use it to block the funnel before removing it from your radiator, so that no fluid spills. If you don’t have a funnel stop, be ready to catch any spills.

Take it for a test drive!

You’re done! If you’ve followed these steps correctly, you’ve now refilled and burped the air out of your car’s radiator.

If you feel like you may have made a mistake or have some concerns, you can give us a call for advice. You can also, bring your vehicle to your local Natrad workshop and let one of our radiator specialists get the job for you.