- Olio Freni DOT4-DOT5

What is DOT 4 brake fluid?

DOT 4 brake fluid is a hydraulic fluid used in automobile braking systems. This fluid is essential for transferring the pressure exerted on the brake pedal to the wheel discs or drums, ensuring efficient braking. Being glycol-based, DOT 4 is hygroscopic, which means it absorbs moisture over time, causing its performance to decrease.

When should you change DOT 4 brake fluid?

It is recommended to change DOT 4 brake fluid every two years or between 40,000 and 60,000 kilometers, regardless of vehicle use. However, in particularly intense driving conditions or in humid climates, it may be necessary to change it even more frequently.

Why does it change?

The main reason DOT 4 brake fluid needs to be changed is its tendency to absorb moisture from the air. This leads to a reduction in the boiling point of the fluid, which can impair the ability to brake effectively. If brake fluid becomes saturated with moisture, it can cause vapor bubbles to form during heavy braking, extending the pedal travel and reducing the efficiency of the system.

In summary, DOT 4 brake fluid is a crucial component in ensuring safe braking, and regular maintenance is essential to keep your vehicle in top condition.

Difference between DOT 4 and DOT 5 brake fluid

Composition

• DOT 4 : DOT 4 brake fluid is a glycol-based fluid, which means it is hygroscopic, meaning it absorbs moisture over time. This type of fluid is commonly used in vehicles with modern braking systems, including those equipped with ABS and ESP.
• DOT 5 : DOT 5 brake fluid, on the other hand, is silicone-based and non-hygroscopic, meaning it does not absorb moisture from the environment. It is best suited for historic or military vehicles and cannot be mixed with other types of fluids such as DOT 3 or DOT 4.

Boiling point

• DOT 4 : Has a boiling point of around 230°C (dry) and tends to reduce when it absorbs moisture, dropping to around 155°C (wet). This makes DOT 4 effective for most road vehicles.
• DOT 5 : It has a higher boiling point, above 260°C , and because it does not absorb moisture, it maintains constant performance even in the long term. However, DOT 5 is not suitable for vehicles with ABS, as it can cause air bubbles during use.

Application

• DOT 4 : It is recommended for most modern cars, especially those with disc brakes or with ABS and ESP systems, where intensive use requires a fluid that can handle high temperatures.
• DOT 5 : It is mainly used for vintage vehicles or in special applications, such as military cars, where the lack of hygroscopicity is an advantage, but it is not compatible with modern ABS systems.

Maintenance

• DOT 4 : Because it is hygroscopic, it must be replaced regularly (every two years or 40,000 km) to prevent performance degradation due to moisture absorption.
• DOT 5 : Being non-hygroscopic, DOT 5 has a longer life and requires fewer replacements over time. However, its limited use and non-compatibility with many modern vehicles reduce its diffusion

Conclusion

The main difference between DOT 4 and DOT 5 brake fluid is in the composition and long-term performance. DOT 4 is more versatile for everyday use in modern cars, while DOT 5 is ideal for special or vintage vehicles that do not have advanced braking systems such as ABS.