Moisture in Brake Fluid – Why?

The brake fluid is an essential aspect of the brake but tends to get contaminated easily. It could get contaminated through dirt, water, and even the air. Once the fluid is contaminated to an extent, it becomes terrible and cannot be used. It is why you need to watch out for moisture in brake fluid.

There are many ways that moisture could get into the brake fluid; majorly the liquid absorbs the moisture from the air.

moisture in brake fluid

Causes of Moisture in Brake Fluid

Brake fluid is hygroscopic, which absorbs moisture from the air. This nature becomes particularly dangerous during the humid season. The brake fluid can absorb moisture that escapes through the brake lines or reservoir. It is usual for the liquid to absorb moisture from damaged hydraulic hoses or brake master cylinder.

The brake fluid in your vehicle mustn’t get exposed to air; the reservoir is fitted with an air-tight cap to ensure nothing gets in. However, when this cap gets damaged, the fluid becomes exposed to a large amount of air from which it could draw moisture.

When brake fluid moisture becomes too much, you begin to see dark brake fluid; this could be dangerous as water deposits in the brake fluid as it could reduce the boiling point and cause parts of the brake system to rust.

Furthermore, the bad brake fluid caused by moisture will reduce the braking condition making the brake sluggish or failing during difficult situations like driving down a slow road. You will have to apply more pressure to the brake pad when driving, among other problems that come with the problem.

How Fast Does Brake Fluid Absorb Moisture?

In normal working conditions, the brake fluid tends to absorb between 1 to 2% water in a year, depending on the temperature and the climate. It could take in even more during the humid condition. You must ensure that the reservoir is closed correctly and the fluid is not exposed to air.

Checking Moisture in Brake Fluid You Tube

Brake fluid will absorb moisture from the surroundings when you pour it into your vehicle’s reservoir. After 18 months, it could absorb up to 3% of water.

What Happens When Brake Fluid Absorbs Moisture?

When brake fluid absorbs moisture, it gets contaminated; in some cases, you can see water floating on the brake. In other cases, the liquid will change color due to the moist corroding parts of the brake system. Once the contaminated fluid begins to circulate through the braking system, it corrodes metal parts and lowers boiling point of brake oil; in this case, your vehicle will experience bad brake fluid symptoms.

Below are some of the symptoms of brake fluid contaminated by moisture.

1. Delay in Braking

One thing is that moisture in the brake fluid attacks the metal parts of the brake, causing them to get corroded, stopping or limiting its movement. When this happens, it delays braking. When you hit the brake, it will take more time to respond.

2. Brake light

Contaminated fluid will trigger your brake or ABS light. While older vehicles may not have ABS lights, the brake light will be triggered. The brake light shows that the brake fluid is either low or something is wrong with it or parts of the brake. Once you see the light come on, it is best to check the brake fluid for contamination or if it is adequately topped up.

3. Excessive pressure when braking

Another sign you will encounter will be with your pedal. Your brake pedal will need more pressure than usual to get the brake to work. It shows liquid in the vehicle but is bad and needs to be changed. If the brake pedal feels soft when you apply the brake, then you might be low on brake fluid.

4. Burning smell

Usually, this does not always happen, but if you notice a burning smell coming from the brake, wheel, and so on. After applying the brakes then, you might have a fluid problem. It may show a problem with significant parts of the brake system, which could be caused by corrosion due to moisture in the brake.

5. Vehicle pulling to the side

When your vehicle keeps pulling to one side whenever you brake, it is a sign that you may have a leaking brake fluid line. The brake fluid may be drawing moisture from the part of the vehicle from which the fluid is leaking.

Sometimes, contaminated brake fluid may show signs of low brake fluid, making it easy to mistake them for fluid contamination. You need to have a brake fluid moisture test. You can use a fluid test pen to measure the electrical conductivity of a liquid in the brake fluid.

Can You Boil The Moisture Out Of Brake Fluid?

Do not try to boil the brake fluid to get rid of the moisture. Brake fluid contains glycol additives. When fluid is mixed in water or moisture and boiled, the water will form a mixture with the glycol additive and evaporate. Which is good, but the bad thing is that the fluid will lose some of its suitable components.

brake fluid moisture

The best way to get the water out of the brake fluid is to change the brake fluid completely. You will have to get the brake oil out of the reservoir and then bleed the brake of all other fluid.


It is usual for your brake fluid to absorb water. It is hygroscopic and will draw water from the air. It is why you need to put measures in place to ensure that it does not absorb too much water quickly. A way you can do that is to ensure that the reservoir cap is adequately tightened and not damaged. Most air gets into the brake fluid from the reservoir cap or the brake fluid line. Also, ensure that there is no leak in the line.

Akindayini Temiloluwa

I am Akindayini Temiloluwa, an automotive expert writer and car enthusiast. I have over three years of experience in the automotive writing niche and have completed over 300 pieces of content from 50 projects. I have vast knowledge and skill in vehicle repairing, all mechanical work, car upgrades and maintenance. My goal as an automotive content writer is to simplify the most challenging concepts for my readers, help them self-diagnose what may be wrong with their vehicles and offer real value for their time.

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