Can You Add Brake Fluid While Car Is Running? Warnings & Precautions

Welcome to the necessary instructions for automobile maintenance. This instruction manual will ensure your safe and pleasurable driving on the road. By these guidelines, we can make every component of the braking system, the guardian of your safety at their optimum capacity. If you are navigating the answer to the question, can we add brake fluid while the car is running? Then you have reached the right market of information.

So Simply put, you can’t top up braking fluid in the reservoir tank when the car is running or the engine is hot. If you are adding braking fluid in a hot braking system then you are playing with dangers and along with yourself you are putting your vehicle in hot water.

We are not just saying no to it, but we will show you how this activity can bring your vehicle to ruin. And can make the braking fluid corrosive for the braking system. Let’s uncover the veil of understanding about do you put brake fluid in while car is running, and should car be running when adding brake fluid. After this we also see that how to add brake fluid to your car.

Importance of Braking Fluid

Importance of adding Braking Fluid in car

Braking fluid takes the crucial and fundamental responsibility of transferring the force from brake pedals to heavy brake pistons. By this, it maintains your command over your vehicle and makes you feel like its king. So if it does not work properly, then driving the car will be like flogging the dead horse. Following things, we need to keep in mind for the health of braking fluid:

  1. Not to add braking fluid when the vehicle is running.
  2. Change the braking fluid when it turns the color to dark brown.
  3. Add the recommended type of braking fluid.
  4. Repair the damage to the braking system caused by corrosion

When Do You Need To Change The Braking Fluid?

Change brake fluid of car

According to the experts and many of the manufacturers of the vehicles, following guidelines are prescribed as the indications for the right time to change the braking fluid:

  1. When braking, the fluid’s color is dark.
  2. When braking fluid is excessively exposed to moisture and dust.
  3. After 2 to 3 years or after 35000 miles to 40000 miles.
  4. If you have poured the wrong braking fluid.

What Damages occur if you Add Brake Fluid While Car Is Running?

damages if add brake fluid in running car

Braking fluid seems to be a divine blessing for our vehicle. But if you fail in maintaining its quality it can be proved as a silent enemy who is eating up the lifespan of the vehicle by corrosion. And dragging you and your dear ones into the danger zone by reducing the efficiency of the braking system. 

Let’s dive into the details of the damages caused by adding braking fluid in a running car or hot braking system

Reduced Braking Efficiency Because of Aeration of Braking Fluid.

If you add braking fluid in a running car or hot braking system, it will cause aeration of the braking fluid. This passage of the air through the braking system will make you experience the spongy brake pedal. So the efficiency of vehicles to stop, especially in emergency conditions, will be reduced.

Contamination of Braking Fluid with Moisture.

The most used types of braking fluids are DOT3 and DOT4. Both are hygroscopic fluids. These have a lot of capacity to absorb water from the environment. So if you add the braking fluid to a hot system, it will consequently raise its temperature. With the rise of the temperature, the braking fluid will expand and its capacity to absorb water will increase.

It reduces the fluid’s effectiveness and can lead to corrosion within the braking system, potentially damaging critical components.

Master Cylinder in Huge Risk.

The braking system is like a fine-tuned orchestra. Every component affects the other part of the system. So if we have drained braking fluid in running cars, then we have pushed an unarmed master cylinder on the battlefield against grave danger. 

The seals of the master cylinder will be damaged because of the creation of pressure surges. If it leaks, it will also damage the diaphragm and other components because of its corrosive nature.  

Hiding the Root Problems under the Carpet.

Imagine you have minor defects with your braking system. If you pour the braking fluid into the hot system, then you will not be able to navigate the underlying problems. But if you top up the braking fluid in a cooled system, that will also help you to see the problems in other parts of the system. 

So neglecting the underlying issues used to set the stage for more damage and unsafe driving conditions.

Making the Braking System a Reaction Funnel.

You can also think of the braking system as the blood vessels, so the right blood type match is necessary for the medical procedure.  You need to be more cautious while adding the braking fluid to it. 

Especially when someone is mixing DOT 3 and DOT 4 then running a car can change the nature of the fluids with the help of excessive heat. This reaction will increase the corrosive ability of the braking fluid.

Contamination of Braking Fluid with Foreign Substances.

The quality of the braking fluid should be pure in the mountain stream. Otherwise, it sabotages your expectations on the road in hilarious traffic. With time, braking fluid gets contaminated by both foreign and internal particles. When you add the braking fluid in a running car or heated system, the capacity of absorbing the contamination increases because of the expansion of the braking fluid.

This contamination will decrease the incompressibility of the hydraulic fluid and it can fail the entire braking system. 

Overfilling of Braking Fluid.

Let me make you acquainted with a chaotic condition. Just think, if the reservoir tank bursts and corrosive braking fluid destroys important components. For your kind information, this will only happen when you have filled the braking fluid more than the maximum limit. 

In the hot braking system, the tubes and master cylinder are expanded. So these can fill the braking fluid more than the maximum capacity. And when the fluid is heated up, the master cylinder can’t afford the pressure. So erupting braking fluid causes collateral damage.

Impact Of Adding Brake Fluid To A Running Car On Brake Booster Vacuum.

It is not only our foot and braking fluid working hard when we push the brake pedal, but there is a brake booster vacuum that also lends a helping hand to the whole process. 

If we add the braking fluid in the running car, it can damage the vacuum line. And the brake booster vacuum is falling back upon this vacuum line. To stop the car without a brake booster vacuum is a hard nut to crack 

You Can Put Yourself In Hot Water.

Adding the braking fluid in a running car is like taking the bull by its horns. Even a single drop out of the reservoir tank can cause flaming, which can hurt your body. And when the engine is on there are the chances of moving the car without your notice, and it can bang with somebody.

So adding flammable hydraulic fluids to the hot system can burn the candle to your health and money from both ends.

How To Add Braking Fluid Properly: Steps To Follow

How To Add Braking Fluid Properly

To avoid the damage from corrosive braking fluid, we need to flush it. These are the steps to change the braking fluid.

You may also read What Happens If You Overfill Brake Fluid?

Step 1: 

Park your car at some safe place and turn the engine off. To remove the wheels, put the car on a jack.

Step 2: 

Remove the old fluid from a master cylinder with some equipment. But don’t make the cylinder completely dried up.

Step 3: 

Drain the recommended type of braking fluid in the reservoir tank up to the maximum limit.

Step 4: 

Start the bleeding of the fluid from the opposite side of the reservoir tank and maintain the correct order of the bleeding fluid from each wheel.

Step 5: 

Find out the bleeder valve with the help of the owner’s manual. Put a pot or attach a pipe to it to release the old fluid.

Step 6: 

Push the brake pedal until the bubbles are stopped. Continue the process for each wheel

Step 7:  

Fill the cylinder with the fluid up to the maximum indicator line. Apply pressure on the brake pedal to check firmness. Now put the wheel on and go for a test drive. See if the braking system is working properly.


Here are some frequently asked questions about the can you add brake fluid while car is running.

Q: What should I do if I am forced to add braking fluid to a hot braking system?

ANS: Firstly, it is not recommended to add braking fluid in the running vehicle’s or hot system. But if it becomes compulsory, then wait for at least 30 minutes.

Q: How to know which type is recommended for my vehicle?

ANS: You need to consult the owner’s manual and the manufacturer. 

Q: What is the difference between hygroscopic and hydrophobic?

ANS: DOT3 and DOT4 are called hygroscopic because these absorb water. DOT5 and DOT5.1 are called hydrophobic because they do not absorb water.


In this modern era, maintenance of automobiles is not a big problem. But for example you are in a hurry to attend a ceremony, you are late from the office, you have embarked on a mountain trip, or you are losing your car race, whatever the conditions are you need to follow the instructions.

Braking fluid acts like a backbone of the vehicle so that it keeps your driving smooth. If you have bad-quality braking fluid, then your car is leading you in the path of treachery. And the braking system will stab you in your back by not following your expectations.  So don’t add braking fluid in running cars. And play any trick that can damage your brake fluid.

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