Can I Add Brake Fluid to a Hot Car

Can I Add Brake Fluid to a Hot Car

As I was driving on a hot summer day, I noticed that the brakes of my car were very soft. Then I checked the brake fluid level and found that it was very low. Then the question came to my head: can I add brake fluid to a hot car?

The answer is yes, you can add brake fluid to a hot car. At around 400 degrees Celsius, brake fluid becomes flammable. However, you should avoid accidental spills on the hot exhaust manifold and spill-related fumes. No brake systems are impacted by adding brake fluid while the car is hot.

So, I did some research and took the necessary precautions to ensure my safety and the safety of my vehicle.

In this article, I’ll explain how I add brake fluid to my car and share the things I found in my research that you must know as a vehicle owner and a driver.

What is Brake Fluid?

Brake oil bottle, Dot 4 brake oil

The chemically-based liquid applied in modern vehicles’ hydraulic braking systems is called brake fluid. When you apply low force to the brake pedal, hydraulics create a lot of force on the brake calipers. If you didn’t have brake fluid, stopping your car wouldn’t merely be possible with your foot.

How does Brake Fluid work?

In a vehicle’s braking system, brake fluid is essential. It transmits the brake pedal’s force to the brake parts. Then brake components such as brake pads and calipers press against the brake rotor to slow or stop the vehicle. When you press on the brake pedal, the brake fluid flows through the brake lines to create hydraulic pressure, which in turn applies to the brakes.

Fluid Protects Brake System from Heat

The heat is generated in the braking process by converting the kinetic energy of the vehicle into heat energy. This heat can cause the brake components and the fluid to get hot. Brake fluid helps to reduce this heat.

What Happens If Brake Fluid Boils?

However, if the brake fluid boils, it can lead to a loss of brake pressure and increased stopping distances. This is why it’s important to change brake fluid regularly to ensure that it has a high boiling point and can continue to function effectively. Brake fluid also gets contaminated over time, and changing it can help ensure the longevity of the brake system.

What Are the Different Types of Brake Fluids?

There are several types of brake fluids, such as DOT 3, DOT 4, DOT 5, DOT 5.1, and mineral oil. Dot brake fluids are most commonly used. Mineral oils are expensive.

Type of Brake FluidDescriptionProsCons
DOT 3Glycol-based fluid that is commonly used in vehicles.– Relatively inexpensive
– Wide availability
– Good for normal driving conditions
– Low boiling point  
– Hygroscopic  
– Every two years, it should be replaced
DOT 4Glycol-based fluid with a higher boiling point than DOT 3.– When compared to DOT 3, it has a higher boiling point.
– More resistant to moisture absorption
– Suitable for high-performance vehicles
– More expensive than DOT 3
– Still hygroscopic
– Every two years, it should be replaced
DOT 5A Silicone-based fluid that is not hygroscopic.– Does not absorb moisture
– Does not damage paint or plastic
– Can last up to five years
– Expensive
– Can cause seal and hose damage if mixed with glycol-based fluids
DOT 5.1Glycol-based fluid with a higher boiling point than DOT 4.– When compared to DOT 4, it has a higher boiling point.
– More resistant to moisture absorption
– Suitable for high-performance vehicles
– More expensive than DOT 4
– Still hygroscopic
– Every two years, it should be replaced
Mineral OilSynthetic fluid which is used in some high-end vehicles.– Not hygroscopic
– More stable than glycol-based fluids
– Does not damage paint or plastic
– Not compatible with glycol-based fluids
– Expensive
– Low boiling point

How Did I Add Brake Fluid to My Car?

Adding brake oil to a car, brake oil bottle, car battery

First of all, I parked my vehicle on a flat surface.

Then I located the fluid reservoir and cleaned the brake fluid reservoir cap to prevent debris from falling into the reservoir.

Next, I removed the cap.

After taking off the cap, I carefully and gradually topped off the brake fluid level in the reservoir until it reached the maximum fill sign.

Then, I securely screwed the reservoir cap back on and drove my car for a short period while braking occasionally.

Finally, once parked on a flat surface, I checked the fluid again to be sure of a successful fill.

Note: It was possible that I needed to see a shop for a brake fluid change if the fluid was particularly dark or contained debris because it might have reached the end of its useful life.


Should car be running when adding brake fluid?

Yes, while a car is running, brake fluid can be poured in. However, it is better to add it with the engine off. Avoid getting the fluid on painted surfaces, as it may damage the paint. Spills should be cleaned up right away with soap and water.

Can low brake fluid cause car not to start?

There are some ways that the braking system can prevent the automobile from starting, but low brake fluid won’t do it. In this way, the brakes do have an impact on a car’s ability to start since the majority of more recent models require that the brake be applied while the car is being started. Older automobiles have not, so the brakes have no impact on vehicle start.

Can you check brake fluid when the car is hot?

Yes, no problem; you can check. But there is a slight impact on fluid levels when the vehicle is hot. For accuracy and safety, it is best to check your car’s coolant and brake fluid when it remains cold.

Do electric cars need brake fluid?

Electric vehicles won’t need their engine oil changed, but they will need other types of fluid changes, like braking fluid. It can become polluted, preventing it from working properly and ultimately resulting in brake failure, just like in normal cars.


I hope you got enough information on adding brake fluid to a hot car. In conclusion, adding brake fluid to a hot car is possible, but it’s important to take precautions to prevent spills and avoid the risk of fire.

Brake fluid plays a crucial role in the braking system of a vehicle, transferring the force from the brake pedal to the brake components. Regularly changing brake fluid can help ensure its effectiveness and prevent a loss of brake pressure, leading to safer driving conditions.

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