What type of brake fluid is commonly used in automotive braking systems?

The commonly used brake fluids in automotive braking systems are DOT 3 and DOT 4. These fluids are hygroscopic, meaning they absorb moisture from the air, which can lead to a decrease in braking performance over time if not replaced regularly. Both DOT 3 and DOT 4 are glycol-based fluids and are used in a wide variety of vehicles due to their effective boiling points and compatibility with most brake system components.

DOT 3 has a minimum dry boiling point of 401°F (205°C), while DOT 4 has a higher minimum boiling point of 446°F (230°C). This makes DOT 4 preferable for high-performance applications or vehicles that undergo rigorous use.

On the other hand, DOT 1 and DOT 2 were earlier standards that have largely been phased out for contemporary automotive applications. DOT 5 is a silicone-based fluid that does not absorb moisture and is commonly used in classic cars or military vehicles, but it is not compatible with the brake systems designed for glycol-based fluids. DOT 5.1 is a glycol-based fluid like DOT 3 and DOT 4, but it is specifically designed to have a higher boiling point. However, its use is less common compared to DOT 3 and DOT 4 in