Oil in Brake Fluid Reservoir – Why?

Having oil in brake fluid is dangerous and can destroy the parts of the brake. People need to understand that oil and brakes do not go very well. It would help if you constantly examined your brake reservoir for oil or other contamination that could cause a brake problem.

You have to understand the causes of oil in the brake liquid, how you can detect or test your brake fluid for oil contamination, and what to do when you find out the fluid has been contaminated.

oil in brake fluid

Causes of Oil in Brake Fluid

There are many ways oil can get to the brake fluid. It could result from human error or a damaged part of the vehicle. It would be best to locate how the oil gets to thebrake fluid in the engine.Below are some of the causes of oil in brake oil.

1. Damaged brake fluid reservoir

The brake fluid reservoir is a part of the engine that stores the brake oil. It is located in the master cylinder. When the brake fluid reservoir is damaged, it could cause all kinds of contamination to quickly find its way into the fluid. It is why oil can contaminate the brake fluid. You need a brake fluid master cylinder replacement when you notice it is damaged.

2. Broken reservoir cap

The reservoir cap is meant to be airtight, keeping all contamination away from the fluid. Once the cap is damaged, it will not be able to do this properly, causing oil spills from the engine to get into the fluid. Try and check if the cap is tightened well and examine for damages. If it is damaged, then you need a new one.

Oil in Brake Fluid You Tube

3. Worn-out gasket seals

One of the familiar places that oil can leak out from under the vehicle’s hood is through the gasket seal. When the gasket seal leaks, oil can leak into the brake fluids.

4. Bad engine servicing

You must pay attention when servicing your vehicle. You may mistakenly pour engine oil in the brake fluid reservoir which can cause oil into the brake liquid. Ensure that when servicing your engine, it is done by a professional. If you serve yourself, ensure you pay close attention and avoid making mistakes.

How Do You Check Brake Fluid For Oil Contamination?

check brake fluid

There are numerous ways to check for brake fluid contaminated with oil. It is simple to notice and identify if you have oil brake fluid. It is because brake fluid and oil do not mix well. So it is easy to tell that there is something wrong with the brake oil by just looking at the brake liquid.

Like when oil is poured into water, oil has the same effect on brake fluid. You can see the oil floating on the fluid. To examine the liquid, open your vehicle’s hood and locate the fluid reservoir. Open it up and take a look at it. If you see apparent oil floating on the fluid, it is contaminated with oil. Also, if the fluid has changed color, it could be due to a change.

Furthermore, you could do the water test. Brake fluid mixes well with water, but oil does not. Get a sample of the brake fluid from the reservoir and a cup of water. Pour the sample of the brake liquid into the water. You will see that the dot 4 brake liquid quickly blends in with water, as you can hardly tell that something has been mixed with water. If their brake fluid is contaminated with oil, you will see the oil residue floating on the water.

There are more advanced ways to check for brake fluid contamination. You could use a test strip to check for copper, moisture, and other substances. The test strip is not expensive, and it is easy to use.

 How Do You Flush Oil Out Of Brakes?

When you notice that your brake fluid has been contaminated, it is best to eliminate it from the vehicle. You cannot significantly decontaminate the fluid when the engine oil contaminates it. You will have to drain the brake oil from the vehicle and have it replaced.

To flush the brake fluid properly, you need the right guide. One that is key to understanding and following. Remember that the procedure to flush the fluid is not added but requires care.

Below is an easy-to-follow guide to have your contaminated car brake fluid reservoir flushed.

1. Ensure to have your safety gear on before you start the procedure to avoid skin injury. You would need at least a glove and safety glasses. Remember that you are dealing with a dangerous substance.

2. Pull over on a leveled surface and ensure that you activate the emergency brakes.

3. Open your vehicle’s hood and locate the brake fluid reservoir. It is usually where the master cylinder is. Open the cap of the master cylinder. Using a syringe or turkey baster, suck out all the fluid in the reservoir.

4. Refill the reservoir with new fluids of your vehicle.

5. Consult your vehicle’s manual to have a knowledge of which order of caliper you will be bleeding brakes or flushing the brake fluid from.

6. The next step is to have the wheels removed. To do this, you must loosen the lug nut, jack the vehicle, remove the nuts, and then the tire. Ensure that you use wheel blocks for the tires to ensure the vehicle does not move during the process.

7. Place a drain pan beneath the wheel and prepare your hose.

8. Loosen and remove the bolt on the bleeder valve and attach the hose.

9. With a friend’s help or any assistance, ask that the brake be pumped about 5 times or when they notice it is stiffer and then push and hold the brake pedal down.

10. Right before the brake pedal hits the bottom, tell your assistant to tell you. Once you are notified, close the valve.

11. Repeat the process with all the wheels, and then lower your vehicle and fill up the brake liquid to the recommended level.

Does Oil Damage Brake Pads?

Having oil on the brake pads is terrible and can damage the brake pad easily. Oil or any form of lubricant directly on the brake pads will stop your brakes from being effective. There is supposed to be some friction between the brake and the rotor. The oil will reduce the friction level needed to stop the vehicle.

Also, motor oil can damage the rubber present in the brakes to be deformed by making it swell. There are many rubber seals in the brakes; when damaged, it will make the brakes stick, leak fluid, or fail. 


When you have oil in brake fluid, brakes and oil are not meant to be. When oil gets into the brake fluid, there is a huge problem. Oil will damage the hydraulic brake system, causing seals, hoses, and other parts to fail. When you notice that the brake liquid has been contaminated with oil, you need to drain the fluid and refill the fresh fluid.

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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