What is the most common type of brake fluid used in vehicles?

DOT 3 brake fluid is the most commonly used type of brake fluid in vehicles, particularly those manufactured from the late 1980s onward. It is a glycol-based fluid, which provides a good balance of performance characteristics, including a reasonable boiling point and compatibility with many vehicle systems. DOT 3 fluid is designed to absorb moisture over time, which helps to reduce the risk of brake fade caused by steam coming from heated fluid, though it does require regular replacement to maintain optimal performance.

The other types of brake fluids have specific applications and characteristics that may limit their general use. DOT 2 brake fluid is less common today, primarily because it has lower performance metrics compared to DOT 3 and is less compatible with modern braking systems. DOT 4 fluid, while advantageous for higher performance vehicles due to its higher boiling point, is not as widely used as DOT 3 in ordinary consumer vehicles. DOT 5, which is silicone-based, is typically reserved for specialized applications as it is not compatible with systems that use other types of brake fluids. Thus, while all these fluids have their specific roles, DOT 3 remains the standard for most vehicles on the road today.