How to Check Brake Fluid

Learn how to check your brake fluid with this in-depth guide covering what it is, how to check it, and how often. Discover how to locate the brake fluid reservoir and symbol, assess fluid condition, and identify when a top-up or replacement is needed through the signs of contamination to keep your braking system safe and efficient.

How to check brake fluid: The complete guide

Brake fluid is a vital component of your vehicle’s braking system, allowing your brakes to function smoothly and efficiently. Over time, brake fluid can degrade or become contaminated, affecting braking performance and safety. Regular checks help ensure optimal function and prevent issues like spongy brakes or longer stopping distances. This guide will walk you through how to check your brake fluid, identify potential problems, and determine when a top-up or replacement is needed to keep your braking system in top condition.

What is brake fluid, and what does it do?

Brake fluid is a vital component of a vehicle’s hydraulic braking system, responsible for transferring the force from the brake pedal into pressure and allowing the brakes to engage effectively. When you press the brake pedal, the brake fluid compresses and moves through the brake lines, activating the brake pads to slow or stop the vehicle.

Brake fluid also acts as a lubricant, helping to prevent corrosion and wear within the braking system. Since braking generates intense heat, brake fluid is specially formulated to withstand high temperatures without boiling or losing effectiveness.

Why is it important to check brake fluid?

Regularly checking brake fluid is crucial for safe and responsive braking. Over time, it absorbs moisture, lowering its boiling point and reducing braking efficiency. Contamination or leaks can lead to spongy brakes, longer stopping distances, and even brake failure. Since brake fluid transfers force from the pedal to the braking system, any issues can severely impact performance. Additionally, brake fluid is highly flammable and can damage paint, so handling it with care—or having it checked by a professional—is essential.

How to check brake fluid

Checking your brake fluid regularly helps you identify low levels, contamination, or other issues before they affect your braking performance. Fortunately, checking your brake fluid is a quick and simple process that requires no special tools. By following these easy steps, you can ensure your fluid is at the correct level and in good condition, helping to maintain optimal brake performance and extend the lifespan of your braking system.

Park on a level surface

To get an accurate reading, park your car on a flat surface, as an incline can affect fluid levels. If your usual parking spot isn’t level, consider using a car park or driveway with no slope.

Locate the brake fluid reservoir

Open the bonnet and find the brake fluid reservoir, usually located at the rear of the engine bay, either on the driver’s or passenger’s side. It’s typically a semi-translucent white plastic container with a black screw-on lid featuring a yellow brake fluid symbol—often shaped like an octagon with a circle and brackets.

Check the fluid level & condition

The reservoir has minimum and maximum markers on the side. If the fluid level is between these marks, no action is needed. However, if it's below the minimum, it must be topped up with the correct brake fluid type.

Additionally, inspect the fluid’s colour. Fresh brake fluid has a light golden hue. If it appears dark, cloudy, or has debris, it may be contaminated and require a brake fluid flush.

Take a short test drive

If you’ve recently topped up your brake fluid, drive around the block and apply the brakes several times to help the fluid circulate properly. This ensures an accurate reading and can also alert you to potential brake issues, such as spongy pedals, unusual noises, or pulling to one side.

When to change brake fluid

Your brake fluid needs to be replaced if it’s low, dark, cloudy, or contaminated, as this indicates moisture buildup and reduced effectiveness. Frequent top-ups may signal a leak, requiring professional inspection. Warning signs of bad brake fluid include spongy brakes, longer stopping distances, or a burning smell after braking. Since brake fluid absorbs moisture over time, delaying a change can lead to brake fade, corrosion, or failure. Check your owner’s manual for specific guidelines and schedule a brake fluid flush when needed to maintain optimal braking performance.

How often should brake fluid be changed?

Brake fluid should be changed every two years or every 24,000 miles, whichever comes first. However, the brake fluid change interval may vary based on factors such as your vehicle’s make and model, the type of brake fluid used, and your driving conditions. High-performance or heavy-duty vehicles may require more frequent changes, while some manufacturers recommend longer intervals. Always refer to your owner’s manual for the specific guidelines for your car. Regular brake fluid checks can also help determine if a change is needed sooner, especially if the fluid appears dark or contaminated.

Brake Fluid FAQs

What causes cloudy brake fluid?

Cloudy brake fluid is a sign of contamination and can compromise your braking system's efficiency and safety. This often occurs due to moisture absorption, as brake fluid is hygroscopic and naturally absorbs water over time, lowering its boiling point and increasing the risk of brake fade. Air or debris entering the brake fluid reservoir can also cause cloudiness, leading to spongy brakes or inconsistent braking. Additionally, old or degraded brake fluid breaks down due to heat and pressure, resulting in a murky appearance. Mixing incompatible brake fluids can cause chemical reactions that alter fluid consistency. If your brake fluid appears cloudy, dark, or dirty, it should be flushed and replaced to ensure optimal braking performance and safety.

Is brake fluid the same as clutch fluid?

Brake fluid and clutch fluid are often the same substance, as most modern vehicles use DOT 3, DOT 4, or DOT 5.1 brake fluid for both the braking and hydraulic clutch systems. However, while they share the same fluid, they serve different functions—brake fluid operates the braking system, while clutch fluid enables smooth gear shifting by transferring hydraulic pressure to the clutch. Some older or specialised vehicles may use different types of hydraulic fluids, so always check your owner’s manual to ensure you’re using the correct fluid for both systems. If your clutch fluid looks dirty or low, it may need a flush and replacement to maintain proper performance.

How long does it take to change brake fluid?

Changing brake fluid typically takes 30 minutes to an hour, depending on the vehicle type, method used, and technician experience. A standard brake fluid flush, where old fluid is drained and replaced, usually takes around 45 minutes. However, if there are air bubbles, contamination, or brake system issues, the process may take longer. DIY brake fluid changes can be more time-consuming, especially if you're unfamiliar with bleeding the brake system. For the best results, it's recommended to have a professional perform the service to ensure proper fluid replacement and braking performance.

In need of a brake fluid change? With over 120 HiQ centres across the country, you're never far from expert brake fluid services and advice.

Visit brake fluid change for more information and to book today.