Should Your Car Be Running When Bleeding Brakes?

Getting your brakes serviced can be an intimidating process, especially if you’ve never done it before. One of the steps involved in servicing your brakes is “bleeding” them, which removes air bubbles from the brake fluid lines. This ensures your brakes work properly by providing consistent hydraulic pressure.

You may be wondering – should I keep the car running while bleeding the brakes? Or is it safe to do with the engine off? Let’s take a deep dive into proper brake bleeding procedures and when it is and isn’t necessary to have the engine running.

What is Brake Bleeding?

Brake bleeding is the process of removing air bubbles from the hydraulic brake system. It is necessary whenever:

  • The brake fluid is changed
  • New brake components are installed
  • Air has entered the brake system due to a leak

Air reduces braking power and makes the pedal feel soft or spongy. Bleeding purges air and vapor pockets out of the brake lines and calipers. This restores proper hydraulic pressure to allow for smooth, firm brake pedal feel.

Here is the brake bleeding process in a nutshell:

  1. Locate the bleeder valve on each brake caliper. This is where brake fluid exits the system.
  2. Attach a clear hose to the bleeder valve to capture old fluid. Submerge the hose in a container.
  3. Loosen the bleeder valve while an assistant pumps the brake pedal.
  4. Allow fluid and air bubbles to escape until new fluid flows out.
  5. Close the bleeder valve and repeat the process for each wheel.

Proper brake bleeding technique is crucial to avoid introducing more air into the system. That brings us to the key question…

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Should The Car Be Running While Bleeding Brakes?

In most cases, the engine should be switched off while bleeding brakes. Here are some key reasons why:

  • Safety – With the engine off, there is no risk of the vehicle lurching forward if the brakes are accidentally released. This protects the technician working under the car.
  • Battery preservation – Running the engine may drain the battery, especially if the process takes a long time. This can be avoided by turning it off.
  • Noise reduction – The engine noise can make it difficult to listen for air bubbles escaping the bleeder valve. Turning it off allows for better focus.
  • No need for pump – Most brake systems don’t require the engine on to manually pump the pedal and bleed the system.

However, there are some exceptions where having the engine on is recommended.

Some modern vehicles use an electric pump to push brake fluid through the system – this pump needs the engine running to operate, so consult your owner’s manual.

Additionally, older vehicles may use engine vacuum for brake assist and require the engine on to replenish the vacuum reserve during bleeding.

Bleeding ABS brake systems usually requires a scan tool and may need the key in the “on” position rather than fully started. Check your manufacturer’s manual for specifications on your particular braking system.

If in doubt about whether your vehicle needs the engine on for bleeding the brakes, consult a certified mechanic to determine if your specific braking system requires the engine to be running.

Turning it off is the safest bet in most situations, unless specified otherwise.

Signs Your Brakes Need Bleeding

How can you tell when your brakes need to be bled? Here are some common indicators:

  • The brake pedal feels soft or spongy
  • The pedal sinks closer to the floor before slowing the car
  • You need to press harder on the pedal to get the same stopping power
  • Braking distance has increased
  • You hear air bubbles when applying the brakes
  • Brake fluid level has dropped in the reservoir

Any of these symptoms mean air has entered your hydraulic system. Bleeding is the solution to restore maximum braking performance. Don’t put it off!

Tips To Bleed Brakes Safely at Home

While professional brake bleeding is recommended, you can bleed brakes yourself if you’re very careful and have help. Follow these safety tips:

  • Never get under the car if it’s solely supported by a jack – use jack stands!
  • Wear protective gloves and eyewear when handling brake fluid.
  • Check that your helper can reach the pedal before you start.
  • Keep rags handy to soak up spilled fluid.
  • Monitor the fluid level in the reservoir to avoid air entering the system.
  • Follow each step slowly and watch for air bubbles to stop before closing valves.

Patience is key for home brake bleeding. It may take 15-20 minutes per wheel to be sure all air pockets are eliminated. Rushing the job will result in poor pedal feel and require starting over.

Signs of Improper Brake Bleeding

If brakes are bled incorrectly, symptoms will return rapidly. Here’s what to watch out for:

  • Spongy pedal comes back after a day or two
  • Pedal continues sinking lower over time
  • Braking distance is still extended
  • Wheels require re-bleeding often

This means air was reintroduced into the hydraulic system due to a mistake in technique. Common errors include:

✘ Releasing pedal with bleeder open
✘ Not refilling fluid level frequently enough
✘ Closing valves before all air escapes
✘ Forgetting to bleed all four wheels

Incorrect bleeding can actually make braking performance worse. When in doubt, have a professional mechanic double check for air pockets in the system.

Frequently Asked Questions

Can I drive with partially bled brakes?

No, you should never drive a vehicle with brakes that have air trapped in the lines. Partial bleeding can make the pedal extremely soft and unreliable. Only drive once all wheels have been fully bled according to proper procedure.

How often should I bleed my brakes?

Annual brake fluid flushes are recommended to avoid moisture buildup in the fluid. Otherwise, bleed them whenever brake work is performed or symptoms of air in the lines appear. Brakes rarely need bleeding in normal driving conditions.

What brake fluid should I use when bleeding?

Always use fresh, clean DOT 3 or DOT 4 brake fluid from a sealed container. Never reuse old fluid, and avoid mixing DOT 3 and DOT 4 types. Dispose of used fluid properly.

Can I bleed the brakes alone without help?

It’s extremely difficult and unsafe to bleed brakes by yourself at home. You need someone to steadily pump the pedal while you open and close the bleeder screws. Invest in a one-person brake bleeder tool if you have no helpers available.

Proper brake bleeding is vital for safe operation of your vehicle. In most cases, it is best done with the car engine switched off as a precaution. Watch for signs of air in the brake system, and never drive without fully bled brakes. Bleeding at home takes patience – if in doubt, seek professional assistance. Keeping your brakes in top form provides peace of mind on every drive.


Properly bleeding your brakes is a crucial maintenance task for safe driving. Take the time to learn the signs that your brakes need attention, invest in the right tools, and partner with an assistant to remove any trapped air bubbles. In most cases, bleeding with the engine off provides protection without affecting the process.

With patience and care, home brake bleeding can restore your pedal to optimal firmness. However, don’t hesitate to call in a professional mechanic if the DIY method proves ineffective or you lack the knowledge to get the job done right. Maintaining an air-free hydraulic system through thorough bleeding ensures you can count on maximum braking power whenever you need it most.

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