What Happens if You Put Power Steering Fluid in the Brake Fluid Reservoir?

Your car is a complex piece of machinery. Each system within it, from the engine to the braking mechanism, relies on its specific fluids to function optimally. These fluids have unique compositions, engineered specifically for their respective tasks, and are not interchangeable.

One common error committed by vehicle owners is using power steering fluid in place of brake fluid. This article uncovers the ramifications of this error and emphasizes the importance of using the correct fluid for each system.

Here’s the quick answer: Putting power steering fluid in the brake fluid reservoir can cause significant damage. It leads to immediate seal swelling, impaired brake functionality, and possibly irreversible damage. To fix it, you need to drain the brake system, replace affected seals, and refill with the correct brake fluid. Always use specified fluids for each system.

Understanding the Fluids: Power Steering and Brake Fluid

Before diving into the consequences of mixing the two, it’s essential to understand what each fluid is and its role. Brake fluid is a type of hydraulic fluid that transfers force into pressure in the braking system. It’s designed to withstand high temperatures without losing its ability to function, hence ensuring that your vehicle stops when needed.

On the other hand, power steering fluid is used in the power steering system to transmit power in the steering system, making it easier for you to steer your vehicle. It’s a type of hydraulic fluid as well but designed for a different purpose, with its characteristics not suitable for high-temperature environments like the brake system.

The Aftermath of Misusing the Fluids

Now, let’s dive into the core of the matter—what happens when power steering fluid is erroneously used as brake fluid?

Immediate Seal Swelling

Power steering fluid contamination will lead to an immediate swelling of seals within the brake system. These seals, typically made of rubber or other elastomers, are not designed to interact with the petroleum-based compounds found in power steering fluid. The resulting reaction causes the seals to expand, potentially blocking critical passageways within the brake system.

Impaired Brake System Functionality

One of the major passages that could get blocked due to seal swelling is the return ports in the brake master-cylinder. The brake master-cylinder plays a vital role in transforming the force from your foot on the brake pedal into hydraulic pressure that slows or stops your vehicle. Blocked return ports mean that this transformation is impaired, causing the brakes to be less responsive, or in severe cases, completely non-functional.

Potential Irreparable Damage

Continued use of a brake system contaminated with power steering fluid can lead to irreversible damage. For instance, the incompatibility between brake fluid and power steering fluid can cause the brake system’s internal components to deteriorate, leading to failure.

What To Do If You’ve Added Power Steering Fluid to Brake Fluid?

If you’ve made the mistake of adding power steering fluid to your brake fluid, don’t panic. However, immediate action is necessary to prevent further damage. Here’s what you should do:

Drain the System Completely

The first step is to drain the entire brake system of all fluids. This is vital to ensure that no contaminated fluid remains in the system. However, this process can be complex and requires specialized tools, and it’s advised to have it done by a professional mechanic.

Replace All Affected Seals

After draining the system, it’s important to replace all seals that could have been affected. This is to ensure that any swollen or damaged seals don’t continue to block passages or cause other problems within the system.

Refill with Correct Brake Fluid

Once the system is drained and the seals replaced, the next step is to refill the system with the correct brake fluid. Again, it’s recommended that a professional mechanic carry out this process to ensure that no air is trapped in the brake lines, which can impair braking performance.

Regular Checks and Maintenance

Following this, regular checks and maintenance should be conducted to ensure that there are no long-term effects of the contamination. This should involve regular brake fluid checks and changes, according to the manufacturer’s recommendation.

Prevention is Better than Cure

The best way to avoid this scenario altogether is to prevent it from happening in the first place. It’s crucial to understand the role of each fluid in your car and ensure that they are used correctly. Always double-check before adding any fluid to your vehicle, and if you’re uncertain, consult your vehicle owner’s manual or a professional mechanic. By doing so, you can save yourself from the costly and potentially dangerous outcomes of misusing power steering and brake fluid.


1. Why is it damaging to mix power steering fluid with brake fluid?

The primary reason why it is detrimental to mix power steering fluid with brake fluid is their incompatibility. Power steering fluid is a petroleum-based product, which can deteriorate the rubber seals used in the brakes when it comes in contact. The swelling and disintegration of these seals can then block critical passages, inhibiting the functionality of the brake system.

2. What are the consequences if you don’t immediately address the issue of power steering fluid in the brake fluid reservoir?

Ignoring the issue of power steering fluid in the brake fluid reservoir could have severe consequences. Over time, the contaminated fluid could cause irreversible damage to the brake system. The new fluid will flow past the chambers without washing out the contaminated fluid, leading to continued swelling of the seals and obstruction of the brake system. This could potentially lead to brake failure, posing significant safety risks.

3. Can you use brake fluid as power steering fluid or vice versa?

Using brake fluid as power steering fluid or vice versa is strongly discouraged due to their different properties and functions. Brake fluid can damage the power steering pump and rack as these fluids are not compatible. Similarly, power steering fluid can damage the seals in the brakes. Therefore, always use the specific fluid designed for each system to ensure the optimum performance and longevity of your vehicle’s components.


In conclusion, using power steering fluid in place of brake fluid in your vehicle is a grave mistake that could lead to severe consequences, including compromised brake performance and irreversible system damage. If this error occurs, prompt action is required to prevent further damage, including draining and refilling the brake system and replacing affected seals. To avoid this scenario, always ensure that you’re using the correct fluid for each system within your vehicle.

Remember, your car is a complex piece of machinery that demands meticulous care. By following manufacturer recommendations and conducting regular maintenance checks, you can ensure that your vehicle continues to serve you safely and efficiently for years to come.

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