Can You Mix DOT3 and DOT4 Brake Fluid? What Mechanics Say

When it comes to driving, the brakes are like our BFFs. They keep us safe on the road. And guess what? Brake fluid is like the ultimate wingman that makes sure the brakes perform their best! It’s kinda like a relay race – the pedal passes the baton to brake fluid, which then stops or slows down your car.

So, today we’re gonna chat about two brake fluids you might have heard of – DOT3 and DOT4. And, oh yeah, we’ll also see if these two can be mixed. Sounds cool? Let’s get started!

Can You Mix DOT3 and DOT4 Brake Fluid?

Are you curious if it is acceptable to combine DOT3 and DOT4 brake fluids? Yes, it is possible. Nevertheless, keep in mind that DOT4 brake fluid has a greater boiling point than DOT3 brake fluid. As a result, if you blend them, the boiling point of the end mix will lie between the boiling points of DOT3 and DOT4 brake fluids.

Although mixing these fluids is technically feasible, it might not be the best idea as DOT3 and DOT4 brake fluids differ in their chemical composition. This could reduce the overall quality of your brake fluid. Additionally, different manufacturers use varying formulas for their brake fluids, making the blending process more complicated.  

The good news is that most car manufacturers prescribe either one type or the other for specific vehicles. Therefore, when replacing your brake fluid, sticking to the recommended type in your vehicle manual can keep your brakes performing at optimum levels and ensure safety.

It’s essential to emphasize that having proper brake fluid quality is crucial for your car’s functioning because it transmits force through hydraulic systems to decelerate the vehicle during braking. Any problems or leaks with your car’s brake system can lead to severe consequences that compromise passenger safety, such as failed brakes. Regularly inspecting and replacing your brake fluid can help you maintain top-notch condition for your vehicle.

The Difference Between DOT 3 And DOT 4 Brake Fluid?

Composition: Glycol EtherComposition: Glycol Ether and Borate Este
Wet boiling point: 205°C/401°FWet boiling point: 155°C/311°F
Dry boiling point: 140°C/284°FDry boiling point: 230°C/446°F

There are crucial aspects that you should keep in mind while choosing the brake fluid for your automobile. One of the most notable contrasting qualities between the DOT 3 and DOT 4 brake fluid is their composition. DOT 3 brake fluid is primarily made up of Glycol Ether, while DOT 4 brake fluid consists of a combination of Glycol Ether and Borate Este.

Another important consideration when choosing brake fluid is boiling point. This is especially true in areas with extreme temperatures, as boiling points can affect the performance and safety of your brakes. In terms of boiling points, DOT 4 brake fluid has a higher dry and wet boiling point than DOT 3.

DOT 3 brake fluid has a wet boiling point of 205 degrees Celsius/401 degrees Fahrenheit, which means it will boil after absorbing just three percent water. Its dry boiling point sits at around 140 degrees Celsius/284 degrees Fahrenheit when no water has been added.

In contrast, DOT 4 brake fluid boasts an impressive dry boiling point of 230 degrees Celsius/446 degrees Fahrenheit and a wet boiling point of 155 degrees Celsius/311 Fahrenheit. This higher boiling point is due to the inclusion of Borate Este in its composition.

It’s worth noting that while both types of brake fluid are compatible with most vehicles, always be sure to check your owner’s manual for any specific recommendations or requirements from the manufacturer.

The Pros And Cons Of Mixing Dot 3 And Dot 4 Brake Fluid

Brake fluids are a crucial component in ensuring safety on the roads. It’s imperative to understand the benefits and disadvantages of mixing different types of brake fluid. Mixing DOT3 and DOT4 brake fluids can have both advantages and disadvantages.

The advantages of mixing the two types of brake fluid include cost-effectiveness and convenience when topping off frequently-refilled brake fluids in an old vehicle. While DOT4 is typically more expensive than DOT3, blending both fluids can be an excellent way to upgrade your brake fluid without breaking the bank.

However, there are some drawbacks to mixing different types of brake fluids as each type has unique properties made for specific vehicles, which may reduce overall performance since they handle differently when under pressure. For example, DOT3 is less viscous than DOT4 brake fluid causing it to flow more easily through the brake lines. When disposed of together with DOT4, it may not flow smoothly as expected, resulting in reduced effectiveness when using your brakes.

Despite earlier claims that you can mix both DOT 3 and 4 types of fluids, refrain from doing it if you’ve just bought or own a high-performance car like exotics or supercars where switching up manufacturer-recommended braking system products affect their functioning. Similarly, if you’re using a combination of one model’s recommended set-up, a blend may cause irreparable damage.


  • Easier vehicle maintenance.
  • Reduce expenses.
  • Remain calm under less meticulous circumstances.


  • Reduce Braking component life span.
  • Lowering its effectiveness at rapid and extreme temperature changes.
  • Affects warranty coverage – if parts become defective due to non-manufacturer fluids used in any modification process.

How To Mix Dot3 And Dot4 Brake Fluid

Mixing Dot 3 and Dot 4 brake fluids is a task that needs to be carried out with utmost care and attention to detail. When you are mixing both types, it’s important to follow some guidelines to ensure optimal performance of your vehicle’s braking system.

Step 1: Park Your Vehicle on a Level Surface

To start, you should move your car to a level surface before mixing any brake fluids. This will ensure that the process is accurate and effective, as it avoids any chances of having an uneven mix.

Step 2: Allow Your Vehicle’s Components to Cool Down

Before mixing the brake fluids, it’s crucial to wait until your car’s components – especially its engine – have cooled down completely. This will help prevent any complications or accidents during the process.

Step 3: Locate Your Vehicle’s Brake Fluid Reservoir

Once your vehicle has cooled down, open the hood and search for the brake fluid reservoir. Spend some time locating it beforehand to avoid any confusion.

Step 4: Remove Your Reservoir’s Cap

Once you’ve found the brake fluid reservoir, remove its cap so that you can assess whether there might be any dirt or road grime inside. You don’t want any grime contaminating your new batch of braking fluid.

Step 5: Clean Out Any Dirt or Grime Inside the Reservoir

If there’s any dirt or grime when you open up your brake fluid reservoir, use a clean rag to wipe it out before pouring in any new brake fluid into this area. If not cleaned out properly, such debris may obstruct your brakes’ functioning and cause complications.

Step 6: Add Equal Amounts of Both Types of Brake Fluid

When adding brake fluids, both DOT3 and DOT4 should be added in equal parts – 50% DOT3 and 50% DOT4 as recommended. In case of uncertainty, refer to the vehicle’s manual to verify the correct combination for your car.

Step 7: Add More Brake Fluid than Needed

When filling up the reservoir with a fresh batch of brake fluid, ensure that you pour in slightly more than needed. That way, after performing a purge, any empty spaces are filled up – this can prevent damage to the brake system.

Step 8: Replace the Cap Back on the Brake Fluid Reservoir

Once you’ve added the new brake fluid to your vehicle, replace the cap on the brake fluid reservoir securely. It would help if you did this before starting up your vehicle again.

Step 9: Check that Your Brake Fluid Level is at the Required Mark

After starting your vehicle, check whether your new brake fluid level is at par with what’s required. If not, open up the reservoir again and add little by little until it reaches the right level.


Now you know the scoop on mixing DOT3 and DOT4 brake fluids! While it is technically possible, it’s definitely not something to brush off. You see, these fluids are unique with varying compositions and boiling points that could give your ride some serious issues and potentially risk your safety. That’s why experts suggest sticking with one type when it’s time to replace your brake fluid. 

If you’re still unsure which type to go for, consider their differences carefully. It may be tempting to save money by mixing them together, but doing so could compromise the lifespan of your braking components and reduce the effectiveness of your brakes at high temperatures.

However, if you do decide to mix them, there are precautions you need to take. Make sure you park on level ground, clean out any debris from the reservoir before topping up with equal amounts of both types of fluid. And most importantly, check the fluid level is correct before driving again.

By following these tips and sticking to recommended guidelines in your vehicle manual, you can ensure optimal performance of your braking system and keep yourself and others safe on the road.


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