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When do I need to change the brake oil?


What is brake oil?

Brake oil, also known as automobile brake fluid, is a fluid used to transfer pressure in the automobile hydraulic brake system, which can maintain the flexibility, effectiveness and safety of braking in hot or cold seasons and at high speed or high load. It is an indispensable part of the hydraulic brake system.

During the operation of the brake system, the brake oil is facing a great threat - water. The brake oil we use is a synthetic oil made of alcohol, which has strong water absorption. If the brake oil has water, because the brake oil will become low when it meets water, the brake oil has not reached the boiling point, and the water has reached the boiling point, so the braking force will drop or fail.

How does it work?

When the driver steps on the brake pedal, the pedal applies pressure to the brake fluid in the brake master cylinder. The brake fluid transmits the pressure to the piston of the brake caliper of each wheel through the pipeline. The piston drives the brake caliper to clamp the brake disc, thus generating huge friction to slow down the vehicle.

In a sealed container or a pipeline filled with liquid, when the liquid is under pressure, the pressure can be conducted faster and more uniformly.

Why does brake oil enter water?

According to the general understanding, the brake system pipeline should be sealed, but the actual situation is not so. In order to ensure the smooth change of liquid level, some models set vent holes on the cover of the reservoir. In addition, the liquid level sensor on the brake oil reservoir is not completely sealed.

Moreover, the brake oil has strong hygroscopicity, which will absorb moisture in the air after long-term use. Frequent car washing or humid environment will lead to safety hazards when the moisture content of the brake oil reaches 3%. Not only will the brake performance be weakened, but the strong air pressure generated by the high temperature may even crush the brake pipeline, resulting in the complete failure of the brake due to the leakage of brake oil.
How to identify the problem caused by brake oil?
If the following four situations occur during driving, it is time to consider replacing the brake oil:
1. When the car brakes, the braking force is light and heavy. When the brake oil deteriorates and the water content exceeds 2.5%, the high temperature generated by frequent braking will turn the water in the brake oil into water vapor, resulting in a large number of bubbles in the brake oil, which will lead to unstable braking force.
2. When the vehicle normally travels to a speed of more than 40km / h, slam on the brake, and the braking distance becomes significantly longer.
3. The brake becomes soft, and the deterioration of the brake oil will make the brake pedal feel soft even if it is pressed to the bottom. Especially after continuous and frequent braking, the feeling of stepping on the brake pedal is much softer and more elastic than before.
4. The brake oil detection lamp shown in the above figure is used by technicians to detect the moisture content of brake oil. If it exceeds 3%, the red light will be on, indicating that the brake oil has almost failed and needs to be replaced in time. It can be found in your test report.
Since water and impurities are completely dissolved in the brake oil, it is difficult to separate them, so the brake oil can only be replaced instead of other treatments.
Although water ingress in the brake oil develops without your knowledge, you don't need to worry too much. Usually, as long as you regularly change the brake oil according to the maintenance manual (generally two years or driving for more than 40000 kilometers), you can do a good job of maintenance and inspection regularly, and you can eliminate hidden dangers in time.
However, if you find that the brake force drops or the brake lags in daily driving, you must check the brake oil in time, because it is likely to be caused by the deterioration of the brake oil.
On the issue of purchasing brake oil, you only need to use the brake oil of the original manufacturer's specified level. Unless it is a high-performance sports car or a modified car, it is not recommended to choose brake oil above DOT4 level.