What happens if you put too much brake fluid in the car?

Brake fluid is a necessary thing for the car because it affects the overall performance of the braking system and the safety of the car. But many drivers do not know or are ignoring the importance of the brake fluid, most of them adding low-quality fluid or adding too much brake fluid in the reservoir.

How brake fluid helps your car?

To better understand the possible problems of overfilling the brake fluid reservoir with too much liquid, let’s recap how brake fluid helps the braking system and how does it affect it in a narrower sense.

The operating principle of a braking system in modern cars is that when the driver presses the brake pedal, at that moment a mechanism is triggered that transfers some force to special brake pads, which slows down the car due to frictional force. During braking, a certain amount of heat is released.

The excess heat can lead to the appearance of steam jams, which, in turn, can provoke a failure of the braking system in emergency situations. So, brake fluid is needed in order to transmit that very force and serve as a pressure conductor at a remote level.

So, what can happen if there is too much brake fluid in the reservoir?

The most common problems that can appear if the brake fluid level is over the maximum are the following:

Faster contamination of the brake fluid.

Due to natural causes, the brake fluid will be contaminated because of rubber wear, copper wear, and some other parts. But if there is too much brake fluid in the reservoir, this process can be accelerated.

Increased leakage risk

During the active operation of the braking system, there can be an important loss of brake fluid if it is in excess because of the overpressure for a variety of reasons and circumstances.

The brake fluid sensor may damage.

If you add too much fluid or there is a higher level in the reservoir, then this can cause damage to the sensor which measures exactly the level of the brake fluid. A faulty sensor leads to false warnings regarding the brake fluid level, and can even trigger the “Check engine light” which can mislead the driver into thinking that the car has other problems.

An increased level of water accumulation in the brake fluid.

The main drawback of the brake fluid is that it absorbs moisture, this is a well-known negative aspect in the automotive field. The presence of water in the brake fluid will significantly reduce its technical characteristics, for example, the boiling point, leading to the potential overheating of the entire braking system and to its total failure.

Additional pressure in the brake fluid reservoir.

If the brake fluid exceeds the required amount, this could lead to additional pressure in the tank which can cause cracks in the walls where the fluid can leak.

Increased wear of the braking system.

Since the role of the brake fluid is to reduce pressure, then the higher the fluid level, the higher the pressure in the braking system. This can overload the brakes causing them to stop working or to work intermittently.

Brake fluid will wear out much faster.

Because it absorbs moisture, the more fluid there is in the tank, the more it absorbs the moisture. This aspect will make the brake fluid lose its properties much faster, and it needs to be changed more often.

Damage to other car parts.

If the level of the brake fluid exceeds the maximum required value, it can leak. Due to the substances in the brake fluid composition, leaks can damage other car parts in the long run.

Brake fluid can freeze in colder temperatures.

This problem is related to water accumulation in the fluid. An exceeded level of the brake fluid will cause more water to accumulate and this can be dangerous in winter because it can freeze.

The boiling point decreases.

This problem is also related to water accumulation, if water accumulates in the brake fluid, then the boiling point will decrease. If there is more brake fluid than needed, then water gathers much faster, and the chances of damaging the entire braking system will also increase.


Too much brake fluid is definitely not a good thing for your braking system. If, however, you added too much it is recommended to remove excess fluid from the reservoir, or if the maximum level is exceeded due to brake fluid wear because of water accumulation, then you need to change it as soon as possible to avoid other problems in the future.

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