Should You Bleed Brakes With the Car On or Off? | Answering Your Questions

Your brakes are a very active part of your car and one of the most important. But when it comes to bleeding car brakes, there’s some confusion about how to approach this process. So the big question is, do you bleed your brakes while the car is running or when it’s turned off?

You should not bleed your car brakes while the car is on and running. For the best results that won’t endanger or damage your vehicle, ensure it is turned off before attempting to bleed your brakes.

In this article, we’ve gathered everything you’ll need to know about the process, why it should be done, and how. If you’re keen on learning more about it, continue reading below.

Jump To Section

What is Bleeding the Brakes of a Car?

“Bleeding the brakes” is a process involving the brake system, wherein a small valve is opened at the calliper to release small and controlled amounts of brake fluid from the system. This is done to release trapped air inside and remove any air bubbles.

Air is compressible, so it’s not something you want inside your brake system. Air could be trapped through an issue or leak in a seal or due to a service procedure or an upgrade, such as replacing the stock flex lines with more durable stainless steel braided lines. However, high temperatures can sometimes cause brake fluid to boil and release gases into the brake’s hydraulic system.

Can I Bleed the Brakes of My Car Myself?

Yes, if you are confident with your automotive repair skills and have the right tools for the job, you can bleed your brakes yourself. Although you can do it yourself, we recommend visiting a mechanic if you aren’t completely confident.

Of all the issues you could have with a car, bleeding brakes is one of the few that you can handle yourself with the right experience and tools. You will need the following tools to successfully and properly bleed the brakes by yourself:

Box-end wrench, which is suited for your car’s bleeder screws (offset head designs generally work best)
Roughly 700ml of extra brake fluid. However, if you are completely replacing and not just bleeding, this would be closer to 2 litres
A 12-inch long section of clear plastic tubing, one that is ID sized to fit just right over the car’s bleeder screws

A disposable container for the waste fluid
A can of brake cleaner
Preferably an extra set of hands to pump the brake pedal

Should You Bleed the Brakes With the Car On or Off?

Generally, your car should be off while bleeding the brakes. This is because the front axles may spin and hit your hands or move off the stands, and it noticeably changes the pressure at which the fluid will exit the callipers and decrease the time to close the bleeder screw before the pedal is hit.

How to Bleed Brakes By Yourself

While bleeding your car’s brakes may sound complicated, it’s something you can handle if you are reasonably confident with cars. Follow these steps to bleed your car’s brakes:

Bleeding Order – The bleeding process should begin at the corner farthest from the driver’s area, which is the rear right. From there, you would go on to the rear left. The last two would be the front right and front left, respectively. Although the order isn’t critical to the bleeding process, it allows the system to be bled in a way that minimises the possible cross-contamination between the new and old brake fluids.
Find the Bleeder Screw – Look for the bleeder screw; it’s usually just behind the calliper body. Remove the rubber cap from the bleeder screw. Put the box-end wrench over the bleeder screw.

Align the Hose – Place one end of the clear plastic hose onto the ‘nipple’ of the bleeder screw, then the other end of the hose over the disposable container for waste fluid.
Depress the Brakes – Ask for help to pump the brake pedal three times. Let them know to avoid releasing the brakes for now.
Empty the Fluid into the Waste Line – Loosen the bleeder screw with a brief ¼ turn to allow the fluid to be released into the waste line. The brake pedal should “fall” into the floor of the car right after the bleeder screw is opened, reminding your assistant to avoid releasing the brakes until told to do so.

Close it Up – Close the bleeder screw and instruct the assistant to release the brakes.
Visual Inspection – Inspect the fluid in the waste line for any air bubbles.
Continue the Process Until Air Bubbles Are No Longer Present – Check the brake fluid levels in the reservoir after you bleed each wheel, adding fluid as necessary.

Spray Down the Bleeder Screws – After all four corners have been bled, use brake cleaner to wipe and dry any surfaces that have brake fluid on them. Avoid spraying the brake cleaner directly on parts made of rubber or plastic, as they can become brittle.
Final Visual Inspection – Inspect the bleeder screw and any other fittings that were moved, loosened, or tightened to ensure no leakages.
Dispose of the Waste Fluid Properly – Keep in mind that used brake fluid should under no circumstances be poured back into the master cylinder reservoir.

Why Would I Need to Bleed My Brakes?

Bleeding your brakes pushes fluid out to remove air bubbles which turn the braking “soft” due to its compressible nature, helping ensure the brakes work correctly. The reduction in hydraulic pressure greatly reduces the braking efficiency, leading to a “spongy” feeling brake pedal.

This unintentional softening of the brake throws off a driver’s expected braking distance and could potentially cause accidents.

How Can I Tell If There Is Air in My Brake Line?

The simplest way to determine if the air in your car’s brake line is if the brake is not responding or is not as responsive as it used to be or as you expect it to be. However, the following symptoms can also indicate air in your brake line:

“Spongy” feeling brake pedal when pressing down
Brakes feel too “soft (e.g. takes a couple of seconds more before coming to a full stop)

The brake pedal goes down to the floor too much when pressed

Will Air Eventually Work its Way Out of Brake Lines?

No, air will not work its way out of a brake line and will need to be bled eventually. The air within the brake lines usually starts as small bubbles and eventually comes together to form a large air bubble. Ignoring this will cause the brakes to fail due to the lack of required pressure from the brake fluid.

What Are the Most Common Mistakes When Bleeding Brakes?

Although bleeding your brakes is a process that most people leave to the professionals, it’s technically something you can do yourself, provided you have the right tools and experience. Here are the most common mistakes you should avoid when bleeding brakes:

Mixing Brake Fluid Types – Back in the day, all brake fluids were created equal. However, there are now varying types that should not be mixed in any way.

Introducing Contaminants into the System – Much like air, you don’t want dirt and grime to enter the brake system as they could corrode or negatively alter the brakes to be soft or spongy, worsening the issue you are trying to fix.
Having the Wrong Tools – Arguably the simplest mistake to avoid is to ensure you have all the supplies (such as brake fluid) and tools on hand, ready to go before bleeding the brakes. Forgetting any tool required for the process will only make your task harder and unnecessarily longer.

Why is My Brake Pedal Spongy After Bleeding?

A soft or spongy brake pedal after the brakes have been bled usually indicates an incorrectly or poorly done job. This could be a result of several things, including but not limited to a brake fluid leak or more air trapped within the brake system.

Check your car’s master cylinder; if the fluid levels are low, the cylinder will suck air into the system. Remember, if you are not confident in your ability to bleed your brakes by yourself or at home, it’s best to seek a professional mechanic.

What Happens if There Is Too Much Air in the Brake Line?

If too much air is in the brake line, there will not be enough hydraulic pressure to keep your braking system as responsive and efficient as possible. Unresponsive brakes are one of the leading causes of accidents on the road, and it’s incredibly dangerous to drive with air in your brake line.

Air, unlike brake fluids, is compressible, which means it will not be able to transfer as much energy and pressure whenever you press down on the brakes, potentially putting you and others at risk. Air bubbles within the brake line usually start as small bubbles before eventually combining to become a large bubble. That’s why it’s essential to have your brake lines bled as soon as you notice any issues with the responsiveness of your car’s brake system.