Why brake fluid should not be topped as pads wear

As brake pads wear down, the level of brake oil in the reservoir wear down. Some wrongly react to this by topping the brake fluid to compensate for the level drop. Brake oil should be topped during pads change.
Last modified
11 Feb, 2024

Brake oil is an hydraulic fluid used in hydraulic brake and clutch systems. They are used in amplifying braking force. It works on the principle of incompressible fluids.

Brake fluid level is the level brake oil should be topped to in the brake oil reservoir. The reservoir has both minimum and maximum brake oil level marks.

Brake fluid level

The practice of topping brake fluid as brake pads wear down is quite common among vehicle owners but is this practice right or wrong?

It is a practice that potentially has a serious safety concern.


Brake oil is introduced into the car braking system through the brake oil reservoir. This reservoir has minimum and maximum level marks and the level should not go below the minimum level mark nor above the maximum level mark at the time of introducing the brake fluid into the brake system.


If there is no leak in the brake system, there is no way the fluid can escape out hence there is no need to top it.


What happens when brake fluid goes below the minimum level?


This makes it easy for air to get introduced into the brake system. The air will get to the master cylinder and the brake becomes ineffective or fails completely. You can read our article on how to stop a car with failed brakes.


Why brake fluid level drops as pads wear down.


As the brake pads wear and gets thinner, the piston further extends out leaving space for more fluid from the reservoir to fill.

Reasons why brake oil should not be topped as pads wear down.


1. This will mask pad wear issues as the level of brake fluid in the reservoir indicates the level of pad wear given that there is no leakage in the brake system.


2. The mistake of mixing different types of brake fluids that are not compatible can happen. This can iccur if the new brake oil being added is different from the brake oil that was previously in the brake system.


3. When new pads are fixed, the brake oil will overflow and it can corrode robbers, paint and other parts it touches.


When should brake fluid be topped?


The brake pad should be topped when all the brake pads are being replaced with new ones.