What type of brake fluid is most commonly used in domestic passenger cars?

The most commonly used brake fluid in domestic passenger cars is DOT 3. This type of brake fluid is a glycol-based fluid that is compatible with most vehicles on the road, providing a good balance of performance characteristics, such as a high boiling point and resistance to moisture absorption.

DOT 3 brake fluid is suitable for a wide range of vehicles and is especially prevalent in those manufactured in the United States. Its lower cost and adequate performance for typical driving conditions make it a popular choice for many manufacturers. Furthermore, DOT 3 fluid is hydroscopic, which means it absorbs moisture over time, ensuring that the boil point remains at a level suitable for standard applications.

While other types of brake fluids like DOT 4 and DOT 5 are available, they cater to specialized needs or specific vehicle designs. DOT 4, for instance, has a higher boiling point and is often used in performance vehicles for enhanced braking under severe conditions. DOT 5 is silicone-based and generally not recommended for vehicles originally designed for DOT 3 or DOT 4 fluids due to compatibility issues. DOT 2, while existing, has fallen out of favor due to its lower performance specifications and is not commonly used in modern vehicles.