What’s the Difference Between Dot 3 and Dot 4 Brake Fluid?

Newton's first law dictates, "Every object in the state of uniform motion will remain in that state of motion unless an external force acts on it." In other words, your car won’t stop unless your brakes work or you get into an accident. We’d prefer you to choose the former method.

However, to have functional brakes, you need to be using the right braking fluid. Many argue between Dot 3 vs. Dot 4 brake fluid, but people miss out on the fact that different braking fluids are essential for different situations. We're here to help set the records straight.

Why We Use Brake Fluid?

Before we get into the difference between Dot 3 and Dot 4, it's essential to understand why braking fluid is so critical. Braking fluid is simply hydraulic fluid, which is stored in the brake lines.

When we apply the brakes, the force produces pressure in the brake lines. This, in turn, cause the fluid to evenly provide strength to each rotor located at the corner of the vehicle. The rotor then provides force to the brake pads, which in turn creates friction in the drum, thus bringing the car to a stop.

Dot 3 Vs. Dot 4 Brake Fluid

How Brake Fluid Works

Brake fluid is a hydraulic fluid that is used in the braking system of a vehicle. It helps to transfer the force from the brake pedal to the brakes, allowing them to slow down or stop the car. The brake fluid also helps to keep the brakes lubricated and prevents corrosion of metal parts.

Brake fluid works by transferring pressure from the brake pedal through a series of tubes and hoses to the brakes. When the brake pedal is pressed, it causes a plunger to move inside the master cylinder, which then pushes the brake fluid through the system. The pressure of the fluid is then transferred to the brakes, causing them to slow down or stop.

The type of brake fluid used in a vehicle depends on its make and model. Different types of brake fluids have different boiling points and viscosity levels, which can affect the performance of the brakes. The most common types are DOT 3 and DOT 4 brake fluids.

DOT 3 brake fluid is a glycol-based fluid that has a low boiling point and is suitable for most vehicles. It is also compatible with water, which helps to reduce the corrosion of metal parts in the braking system.

DOT 4 brake fluid is a borate ester-based fluid that has a higher boiling point than DOT 3 and is more resistant to water. This makes it ideal for high-performance vehicles that require a higher boiling point. It is also more resistant to corrosion, making it a better choice for vehicles that are exposed to extreme temperatures or moisture.

Dot 3 vs Dot 4 Brake Fluid – Differences in between

If you have a look at your brake oil cap, you’ll notice the company mentions to use Dot 3 or Dot 4 brake oil.

Both are available at quite different prices and are necessary for specific situations. These differences are discussed below to help you choose one that fits into your requirements.

Targeted Type of Driving and Car

We've mentioned both these points together as they are in correlation with each other. Braking the fluid is strongly intertwined with how you use your vehicle.

If you're someone who likes to drive rough, you'll also be involved in rigorous forms of braking. This will require precision braking because of a split-second, and the difference here could become the difference between life and death. Thus, for you, Dot 4 fluid would be perfect, given its high boiling point.

On the other hand, Dot 3 users are mainly targeted as regular drivers. These people drive their cars regularly, such as for commuting. For them, harsh braking isn't entirely necessary, and Dot 3 fluid should do just fine.

Dot 3 users are the main drivers of regular road cars, such as sedans and hatchbacks. On the contrary, Dot 4 is what is used mainly in police vehicles, sports cars, and SUVs.

Varying Boiling Points

The boiling point is one of the most noticeable differences that make Dot 3 and Dot 4 comparable. As we've learned in 6th-grade physics, when you heat any material solid, liquid, or gas, it tends to expand.

In an environment that is close to your engine bay, things are supposedly getting very hot. And if your braking fluid easily expands, it could be a cause of concern.
Dot 3 fluid has a lower boiling point than Dot 4, giving Dot 4 the upper hand in this case. The lower boiling point means the liquid is highly likely to absorb water.

This is also known as the wet boiling point and occurs during regular driving when you take off the reservoir cap. These can cause damaging effects to your braking system over long periods.

Boiling Capacity

The boiling capacity of fluid indicates how well it'll work with a different medium. Since, you cannot eliminate the chance of the brake fluid being compromised.

Dot 3 is compatible to work with both water and air, as its composition is not as sensitive to these foreign elements.

However, even though Dot 4 works quite effectively with air, the same cannot be claimed for its wet boiling capacity. The performance you’ll be getting comparatively would be worse than in ideal conditions.

Chemical Structure

Another point of difference possessed by the two-fluid is their chemical makeup. Dot 3 braking fluid is based on diethylene glycol (DEG) structure. This helps the braking fluid hold up in heat, dry, and wet conditions. Making it great for an everyday driving companion.

Dot 4, on the other hand, is made up of a glycol and borate ester structure. The borate ester helps the fluid deal with higher temperatures and makes it highly resistant to water. This means that it won’t allow your metal components present in your brakes to be corroded.

What are Brake Fluid Ratings, and What do They Mean?

Brake fluid ratings are a way of measuring the performance of brake fluids. The ratings are based on the boiling point, which is the temperature at which the fluid begins to vaporize. The higher the boiling point, the better the performance of the brake fluid.

The most common rating system for brake fluids is known as DOT (Department of Transportation) ratings. These ratings range from DOT 3 to DOT 5.1, with DOT 3 being the lowest and DOT 5.1 being the highest.

DOT 3 brake fluid has a minimum dry boiling point of 205°C (401°F) and a minimum wet boiling point of 140°C (284°F). This type of fluid is suitable for most vehicles and is compatible with water, which helps to reduce the corrosion of metal parts in the braking system.

DOT 4 brake fluid has a minimum dry boiling point of 230°C (446°F) and a minimum wet boiling point of 155°C (311°F). This type of fluid is more resistant to water than DOT 3 and is suitable for vehicles that are used in high-performance applications.

Frequently Asked Questions

1. Can I use DOT 4 instead of DOT 3?

Yes, you can use DOT 4 instead of DOT 3. However, it is important to note that DOT 4 has a higher boiling point than DOT 3 and is more resistant to water. This makes it ideal for high-performance vehicles that require a higher boiling point. It is also more resistant to corrosion, making it a better choice for vehicles that are exposed to extreme temperatures or moisture.

2. Are there any disadvantages of mixing DOT3 with DOT4 brake fluid?

Yes, there are some potential disadvantages of mixing DOT 3 and DOT 4 brake fluids. The most significant disadvantage is that the boiling point of the mixture will be lower than either type of fluid alone. This can lead to a decrease in performance and an increased risk of brake failure. Additionally, mixing different types of brake fluids can cause incompatibility issues, which can lead to corrosion or other damage to the braking system.

3. What is the best DOT 4 brake fluid?

The best DOT 4 brake fluid is one that meets or exceeds the minimum requirements for dry and wet boiling points. Additionally, it should be designed to resist corrosion and provide superior performance in high-temperature applications. Some of the top brands of DOT 4 brake fluid include Castrol, Motul, and Valvoline.

4. Does DOT 4 brake fluid absorb water?

Yes, DOT 4 brake fluid does absorb water. This is why it is important to check the level of brake fluid regularly and replace it if necessary.

5. Why is DOT 4 brake fluid preferred?

DOT 4 brake fluid is preferred because it has a higher boiling point than DOT 3, making it more suitable for high-performance vehicles. Additionally, it is more resistant to water and corrosion, which helps to protect the braking system from damage.

The Difference between DOT 3 and DOT 4 Brake Fluids


In this battle of Dot 3 vs. Dot 4 brake fluid, it's no surprise that there are no winners. Both fluids, even though performing the same task, are designed to serve different individuals.

If you're the type whose drifting skills are famous in the streets, then Dot 4 is right for you. And if you're just trying to get to work, then Dot 3 should do you fine.

John D. Archer

John D. Archer is a mechanical engineer and writer based on the area of automotive accessories at brakeshub.com, A resident expert and professional, John is passionate about all things automotive and loves to share his knowledge. He has good experience in all kind of automotive accessories. He has worked as a chief mechanical engineer in some reputed automotive garage firm.

Click Here to Leave a Comment Below 0 comments

Leave a Reply: