The Ultimate Guide to Brake Fluid

What is brake fluid and how does it work?

Brake fluid is a hydraulic fluid that transfers pressure from the brake pedal to the brake callipers, using force to squeeze the brake pads onto the discs. This friction between the brake pads and the discs slows down the wheels and stops the car.

The most common type of brake fluid used in cars is glycol-based, made of a mixture of glycols and other additives. This type of brake fluid is known for its high boiling point, which makes it resistant to vaporisation and boiling.

This is important because when brake fluid boils, it creates air bubbles, which can cause the brake pedal to feel spongy and reduce braking performance.

In addition to glycol-based brake fluid, there is also silicone-based brake fluid, which is used primarily in racing applications.

This type of brake fluid has a higher boiling point than some glycol-based brake fluids, making it ideal for high-performance applications.

However, it is incompatible with most rubber seals and hoses, so it should only be used in vehicles with a complete silicone-based system or aftermarket stainless brake lines manufactured by companies such as Hel Performance.

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Types of brake fluid

As mentioned earlier, there are two main types of brake fluid: glycol-based and silicone-based. Within these two categories, there are several different types of brake fluid that are designed for different applications and vehicles.

Wet and dry brake fluid boiling points

It's important to consider both the dry and wet boiling points regarding brake fluid. The dry boiling point is the temperature at which brake fluid will begin to boil when it is fresh and unopened.

On the other hand, the wet boiling point refers to the temperature at which brake fluid will start to boil after it has absorbed 3.7% water.

This usually happens after approximately two years of use, therefore is highly recommended to replace brake fluid every 1-2 years to ensure optimum performance and safety.

DOT 3 brake fluid is typically formulated with a glycol-ether base. Its minimum dry boiling point is 205°C, while its wet boiling point, measured with about 4 percent water mixed in the fluid, is 140°C.

It is suitable for use in regular vehicles that are used for typical purposes such as commuting.

Dot 4 brake fluid is very similar to DOT 3 but with additives that increase the minimum boiling points. DOT 4 fluids have a superior dry boiling point but require more frequent changes.

DOT 4 fluids designed for racing or performance cars can significantly exceed the minimum boiling points – they're sometimes referred to as Super DOT 4 fluids.

Regular DOT 4 is appropriate for standard vehicles with a typical dry boiling point of 230°C and wet boiling point of 155°C.

Dot 5 brake fluid is incompatible with any other brake fluid type. DOT 5 doesn't attract water, acts as a rust preventer, and doesn't harm paint. It's also costly, silicone based, and is outperformed by speciality DOT 4 fluids.

Unless your car is designed to run DOT 5 or has a specific reason to run it, you can safely ignore this fluid. The general dry boiling point is around 260°C, with a wet boiling point of 180°C.

DOT 5.1 brake fluid has similar chemical properties to DOT 3 and 4 but has a lower viscosity. It has the same minimum wet and dry boiling points as DOT 4.

However, DOT 5.1 is required by some vehicles for efficient operation. 

It's important to note that mixing different types of brake fluid can be dangerous and should be avoided at all costs. This can cause the brake fluid to lose effectiveness and cause brake failure.

Some brake fluids have a higher wet and dry boiling point than the standard versions, such as the Motul RBF 660 brake fluid. This fluid is DOT4, but instead of 230°C dry and 155°C wet, it can withstand 328°C dry boiling and 204°C Wet.

This specific brake fluid is much better for track-focused use as the braking system gets much hotter, where you will likely boil the standard fluid.

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Importance of brake fluid for vehicle safety

Brake fluid is one of the most critical fluids, as it is responsible for transmitting the force from the brake pedal to the brake callipers.

Without brake fluid, your vehicle couldn't stop effectively, putting you and other drivers at risk of accidents.

Maintaining your brake fluid is crucial for your safety on the road. Over time, brake fluid can become contaminated with moisture, which can lower its boiling point and reduce its effectiveness.

This can cause the brake pedal to feel spongy and reduce braking performance.

Regularly checking and changing your brake fluid is essential for maintaining the safety and reliability of your vehicle's braking system and ensuring it's closer to the dry boiling point than the wet.

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Signs that your brake fluid needs to be changed

There are several signs that your brake fluid needs to be changed. One of the most common signs is a spongy brake pedal, which can indicate air in the brake lines or that the brake fluid is contaminated.

This could be a few things: a leak in the line, it wasn't bled correctly beforehand, or it has naturally gathered air over time. Another sign is a brake pedal that goes to the floor, indicating a leak in the braking system or that the brake fluid is low.

The last sign is when bleeding brakes; if you notice the fluid isn't coming out clear, it may be worth a full flush. The discolouration could be dirt, rust or anything in between, but it will still degrade the brake fluid's performance as it's now contaminated.

If you notice either of these signs, inspecting your brake system as soon as possible is essential. Ignoring these signs can lead to brake failure and put you and other drivers at risk of accidents.

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How to check your brake fluid

Checking your brake fluid is a simple task that can be done at home with little to no tools. To check your brake fluid, follow these steps:

1. Park your car on a level surface and turn off the engine.

2. Open the bonnet and locate the brake fluid reservoir. It's usually located on the driver's side of the engine compartment and is labelled "brake fluid."

3. Check the level of the brake fluid. The reservoir should be filled to the "max" line. If it's below the "min" line, you'll need to add more brake fluid.

4. Check the colour of the brake fluid. Fresh brake fluid should be clear or slightly yellow. If the brake fluid is dark or brown, it's time to change it.

5. Replace the brake fluid reservoir cap and close the bonnet.

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Best practices for maintaining brake fluid

It's important to prioritise the maintenance of your vehicle's brake fluid to ensure your braking system's safety and reliability. To achieve this, there are several best practices that you should follow.

Firstly, it is recommended that you regularly check and replace your brake fluid as needed. This will help ensure that your brake fluid remains at an appropriate level and can effectively transmit hydraulic pressure.

Additionally, it's crucial that you only use the type of brake fluid that your vehicle's manufacturer recommends. Mixing different types of brake fluid can have negative consequences and should be avoided at all costs.

To further maintain the quality of your brake fluid, it's essential always to keep the brake fluid reservoir cap tightly secured. This will prevent contamination from entering the brake fluid and compromise its effectiveness.

Lastly, if you need more confidence in doing this yourself, it is highly recommended that a professional mechanic inspect your brake system regularly.

They will be able to identify any potential issues early on and help ensure that your braking system remains in top condition. Following these best practices can help ensure your vehicle remains safe and reliable on the road.

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Brake Fluid FAQ's

There are several myths and misconceptions surrounding brake fluid. Here are a few common ones debunked:

Q: Does Brake fluid ever need to be changed?

A: Brake fluid should be changed every two to three years or as your vehicle's manufacturer recommends. We recommend changing it as soon as possible if there is any discolouration.

Q: Is all brake fluid the same?

A: Different types of brake fluid are designed for different applications and vehicles. For example, DOT 5 is silicone based, whereas the other types are not, and all variations have different boiling points.

Q: Is it okay to mix different types of brake fluid?

A: Mixing different types of brake fluid can be dangerous and should be avoided at all costs.

Q: Does Brake fluid need to be checked if there isn't a problem?

A: Checking your brake fluid regularly is essential for maintaining the safety and reliability of your braking system.

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High Performance Brake fluid brands

Numerous brake fluid brands are on the market, from standard options to those designed for racing. Obtaining brake fluid nowadays is a breeze, with various sources available.

However, for those seeking high performance on the road or track, we strongly recommend these top 3 brake fluid brands that boast higher wet and dry boiling points than conventional brake fluids.

Motul

Motul is our go-to brand for brake fluid, and we always keep multiple bottles of their products on the shelf.

Their extensive line of brake fluids includes options for DOT 3, DOT 4, and DOT 5.1, as well as Racing Brake Fluids such as the Motul RBF 660, which is by far the most popular fluid we sell.

Whether your car is fitted with ABS or ESP systems or you're driving in normal or extreme conditions, Motul has the perfect solution for your specific needs.

PBS Performance Brake Solutions

PBS has already made a name for itself in the racing industry with its Protrack and Prorace brake pads.

Their two lines of racing brake fluid, the 600max and 660max, have also been recognized for their superior performance.

These fluids have higher boiling points than the standard DOT4 fluid, similar to the Motul equivalent. Racing enthusiasts can rely on PBS for their well-stocked products, easily accessible in just a few days.

Choose PBS for high-quality racing products that won't let you down.

To learn more, we have a performance brake pads article outlining everything you need to know.

Mobil

It's important to note that Mobil is a reputable brand in the oil and lubricant industry with a long-standing history and a public trading status.

Their brake fluid is safe, meets all necessary specifications, and is offered at a reasonable price.

Their products are widely available in major retail stores and outlets such as Halfords, making it a brand worth considering despite not being carried by us.

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Conclusion

Brake fluid is vital to your car's braking system, transmitting the force from the brake pedal to the brake callipers.

Choosing the correct brake fluid for your car and maintaining it properly is crucial for your safety. In this ultimate guide, we've covered everything you need to know about brake fluid, including its types, composition, boiling points, compatibility, and maintenance.

By following these tips and best practices, you can ensure the safety and reliability of your vehicle's braking system for years to come.

If you are still unsure of anything in this article, please contact us, and if it was helpful, please let us know in the comments section below.