What Happens If You Overfill Brake Fluid? 12 Reasons Not To Do It

All mechanics will tell you to regularly check up and change your brake fluid. But no one will tell you what happens if you overfill brake fluid, or what to do about it. Read on to find more.

Overfilling brake fluid can cause several problems with the brakes of your vehicle.

If you happen to overfill the master cylinder with brake fluid, it can cause issues like an overheated brake system, brake pads wearing faster, and brake drag, to name a few.

An overfilled brake fluid is as disastrous as an underfilled brake fluid, 

Brake fluid is an essential part of your vehicle’s braking system. And needless to say but proper braking is critical for your and your family’s safety. You should resolve any issues with the braking system as soon as possible to avoid any significant problems.

Read on below to find out what purpose a brake fluid serves, what will happen if you overfill it and how to resolve the issue. 

What Happens If You Overfill Brake Fluid

Putting Too Much Brake Fluid In Your Car

Brake fluid is one of the essential components of your vehicle braking system. It is a hydraulic fluid that is stored in the master cylinder.

When you apply pressure on the brake pad, this fluid travels to the pipes to apply pressure on the calipers. It then pushes the piston in the caliper out, which applies pressure and pushes the brake pads to the rotor, effectively slowing down the vehicle and bringing it to a halt.

Brake drag is one of the common symptoms of an overfilled brake fluid reservoir.

This happens when the brake pads or shoes do not disengage completely after releasing the brake pedal.

Overfilling of the brake fluid will cause pressure on the brake pads and push them against the calipers. This constant push of the brake pads will result in brake drag.

If you find the issue of brake drag after you have had some brake job done on your vehicle, then an overfilled brake fluid is probably the main reason.

You might like to read: Should I Open Brake Fluid Reservoir When Changing Brakes?

What Happens When You Overfill Brake Fluid In Your Car

Some of the common issues that can occur in your vehicle when you overfill brake fluid in the car include:

#1. Increased Risk Of Leakage 

There is an increased risk of leakage with too much brake fluid in the reservoir. When you apply the brakes, or during other braking operations on an overfilled brake fluid, it can cause extreme pressure on the fluid. This pressure will result in brake fluid leakage.

#2. Overheating Of The Brake Fluid

When you press the brakes, the brake fluid pushes out of the master cylinder to the pipes. It causes the brake fluid to heat up.

Brake fluid expands when it heats up, but overfilled brake fluid leaves no space inside the master cylinder to expand. It results in overheating of the brake fluid.

What Happens If You Overfill Brake Fluid

#3. Damage To The Brake Fluid Sensor 

A brake fluid sensor is responsible for measuring the brake fluid level in the reservoir. When there is too much brake fluid in the reservoir, then it can cause damage to the sensor.

A damaged sensor will lead to false readings of the brake fluid level. It can also lead to the check engine light signal turning on, which will lead you to think that your vehicle has serious issues.

Also read: What kind of brake fluid is used in Harleys?

#4. Brake Fluid Will Contaminate Faster 

Brake fluid will contaminate with wear of several parts like rubber and copper material of the brake system. Having too much brake fluid will increase the process of contamination.

#5. Water Will Accumulate In The Brake Fluid Much Faster 

One of the main issues with brake fluids is the absorption of water. With higher levels of brake fluids, water will accumulate in the fluid at a faster rate. It will result in several other issues in the braking system.

#6. Brake System Becomes More Prone To Wear 

Brake fluid helps reduce the pressure inside the braking system. With higher brake fluid levels, there will be more pressure inside the braking system, which will result in overloading the brakes. It can lead to brakes seizing or stopping altogether.

You might like to read: Can You Use Brake Cleaner As Starting Fluid?

#7. Higher Pressure Inside The Brake Fluid Reservoir

When too much brake fluid, it can result in high pressure inside the brake fluid reservoir. It will then lead to cracks in the reservoir and eventually leak the brake fluid. 

#9. Loss Of Brake Fluid Capabilities 

Brake fluid absorbs moisture, resulting in the brake fluid losing its capability to slow the vehicle down. With too much brake fluid, there is higher moisture absorption, and thus the brake fluid will lose its capabilities much faster.

#10. Brake Fluid Will Freeze

Freezing of brake fluid happens due to the water content in the fluid. With more brake fluid in the reservoir, it will absorb more water and thus has a higher chance of freezing once the temperature drops.

#111. Car parts May Damage 

With higher brake fluid levels, it can leak outside and reach other parts of your car. The brake fluid composition may damage the car parts in the long run.

#12. Lowered Boiling Point Of The Brake Fluid 

With a high brake fluid level, it will absorb too much moisture, which will lower the brake fluid’s boiling point. There is an increased risk of damage to the braking system with the lowered boiling point.

What Happens If You Overfill Brake Fluid

Frequently Asked Questions:

#1. What happens if I overfill my brake fluid reservoir? 

It will wear out your brake pads quickly.

Overfilling the brake fluid reservoir can cause several issues with the braking system. Overfilling the brake fluid results in constantly applying pressure onto the brake pads, resulting in faster wear of the pads. 

Overfilling of brake fluid does not leave any space in the brake fluid reservoir to allow the fluid to expand when heating, resulting in overheating. Since the overfilled brake fluid applies constant pressure, it can result in brake drag.

#2. Can brake fluid be too full? 

Yes, and you need to be careful that you don’t do it for reasons we explained earlier.

Yes, brake fluid can be too full. It is possible to overfill the brake fluid reservoir while refilling it. Most of the brake fluid reservoir comes with a marking of max line to indicate the level up to which it is ideal for filling brake fluid. 

Still, there is a chance that you or your mechanic might have overfilled the reservoir either accidentally or unknowingly. Overfilling brake fluid can result in several issues with the braking system, so you should empty it if the brake fluid is too full.

What Happens If You Overfill Brake Fluid

#3. What happens if you overfill your brake master cylinder?

It can cause your braking system to go haywire

If you overfill your brake master cylinder, then it can cause a severe impact on your braking system. If the brake fluid is overfilled in the brake master cylinder, it will increase the pressure and create a constant push on the brake pads, which will quicken the wear out process. 

Overfilled brake master cylinder can also cause overheating due to no space for the fluid to expand. It can also result in brake drag because of increased pressure.

You might like to read: Why Is My Brake Fluid Green?

Final Words

It is possible to overfill the brake fluid reservoir while refilling it, and that can cause several short or long-term problems in your vehicle. Overfilled brake fluid will cause the brake pad to constantly push against the calipers whether you press them or not. 

It will cause the brake pads to wear out faster. Also, the constant push against the calipers will result in brake drag. Since the reservoir is overfilled, the fluid will not have space to expand, resulting in overheating.

Thank you for reading, we hope this answers your questions. If you have further doubts, do drop us a word in the comments section.

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Sean Mendez

Hi, I am Sean, a self-confessed petrolhead. I live in Boise, Idaho with a busy family of four and our energetic Labrador retriever. Thank you for visiting my website. You can find my email on the contact page.

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