Can You Put Dot 4 in A Dot 3 System? Technical Opinion

Brakes are very important in a motor vehicle. Their main function is to stop the motion of a vehicle. Some brakes use air, and they are called pneumatic brakes. While other brake systems use fluid, and they are called hydraulic brakes. In hydraulic ones, the choice of brake fluid is very important. These fluids are categorized by many standards.

The US uses a system called dot. This system has categories under dot 3, dot 4, dot 5, and dot 5.1. The grouping implies that before substituting one brake fluid for the other, you must know if it is safe. You can commonly replace Dot 3 with Dot 4. Now, the question you may have is, can you put dot 4 in a dot 3 system? We will get to that shortly, but let’s delve into what dot means.

can you put dot 4 in a dot 3 system

What does it mean DOT in brake fluid?

The acronym DOT stands for Department of Transport. This is a department in the US government responsible for transport. The acronym normally comes with a number representing a particular brake fluid category. The dot system groups them according to their boiling point, composition, and related properties. Most vehicles use dot 3 or dot 4. This family of brake fluids covers light vehicles, medium, and even heavy-duty vehicles.

There are times when you may also wish to know which brake oil works for your car. Such details are important in understanding brake fluids. Another important aspect to find out is, will dot 4 work with dot 3 in various engines? This is because the two brake oils are readily available on the market.

In some countries, the Society of Automotive Engineers categorization is still in use. This one also comes with numbers that speak to the type of fluid at hand. In other parts of the world, ISO standards are still very active. But DOT is still the popular classification among many vehicle manufacturers. The system is commonly used around the globe in many countries.

Can you put dot 4 in a dot 3 system?

Yes, you can put dot 4 in a dot 3 system. The bottom line is that the two systems are compatible with each other with only minor differences. For a start, dot 3 and dot 4 brake fluids are both glycol-based. This means that they are compatible with the main chemical composition. There is also small difference in the boiling point between the two fluids which also translates to the systems.

But this is a minor issue and cannot amount to bigger complications. The system that uses dot 3 will function well without problems when you use dot 4. Therefore, dot 4 in dot 3 system will not bring problems to your brakes if the brake pad thickness is okay.

Potential Benefits

Utilizing DOT 4 in a DOT 3 system can potentially offer some benefits. The enhanced thermal stability can prevent brake fade during prolonged or severe braking, offering a safer and more responsive braking experience. Furthermore, DOT 4 fluid may provide better resistance to water absorption, thereby prolonging the lifespan of the brake system components.

Points to Consider

While it is safe to replace DOT 3 with DOT 4, it is crucial to avoid mixing it with DOT 5 brake fluid, which has a silicone-based composition and is not compatible with the glycol-based DOT 3 and DOT 4 fluids. Moreover, frequent changing of brake fluid is advised as it tends to absorb moisture over time, which can lower its boiling point and lead to decreased performance.

Differences between dot 3 and dot 4

There are several differences between dot 3 and dot 4. These details are important when you consider mixing dot 3 and dot 4 in the same system. Dot 3 contains Glycol ether with a dry boiling point of 205 degrees Celsius. On the other hand, dot 4 has glycol ether and Borate ester. The dry boiling point for this type is 230 degrees Celsius. The other important fact about dot 4 is its lower viscosity.

As the numbers show, the boiling point for dot 4 is higher than the one for dot 3. This is expected because dot 4 is an improvement on dot 3 and thus brings in added quality. Therefore, chemically, the two brake oils are different.

Can you mix dot 3 and dot 4?

This is one question that many have wondered. As discussed earlier, the two brake oils contain Glycol. Attempting to mix the two fluids brings them together with added advantages. Their boiling capacity is similar, and they are chemically compatible. The slight variation in boiling points will not affect its performance. Thus, you can safely mix the two fluids.

Does it matter which brake fluid I use?

The choice of brake fluid depends on many factors. Some of them hinge on the ability of the fluid to absorb heat. While the most important property depends on its ability to transfer pressure. When a particular type of brake fluid is chosen, it should have the properties required for the task. Thus, whether you are using dot 3 or dot 4, there are some differences you may expect.

But if you pick just any fluid for your brakes without following the recommended one, you should expect poor performance. The brake fluids are not universal in application and require attention when selecting.

What happens if you use wrong brake fluid?

When you use wrong brake fluid, you feed the system with poor quality and expose it to failure. At times you may even use good quality of the wrong type. This will also not produce good results because the properties are mismatched. Some brake fluids may end up causing corrosion to your components.

Other wrong fluids can end up causing brakes to loose, overheat and fail before their full lifespan. To amplify this, you can consider the properties of dot 3 vs dot 4 vs dot 5 and see. The differences among them range from composition to boiling points and viscosity. Each one is specific for a particular application. Some fluids work very well with heavy-duty vehicles, while others work well under light vehicles.

Wrong fluids spell trouble during and after they are put to use. Such oils will not work as expected because the manufacturer did not test them for that purpose.

dot 4 in dot 3 system


The choice of brake fluid should never be rushed. Can you put dot 4 in a dot 3 system? You can put dot 4 in a dot 3 system because the two fluids can blend with each other very well. At the same time, you cannot pick any brake fluid for any given system. This can cause brake failure, overheating, ineffective braking, and many more problems. When you use the popular dot standard, you will have a variety to pick from and get the best results.


Mr. Shafiqule Islam is a graduated Mechanical Engineer and has more than 15 years experience of repairing and maintenance of different brand vehicles like Toyota, Mitsubishi, Ford, Mercedes, BMW etc. He is also giving training to Mechanics. He has started writing to share his practical knowledge to Vehicle Owners, Drivers and Mechanics to keep their cars at best fit.

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