ASE Auto Maintenance and Light Repair Certification (G1) Practice Test 2026 - Free Auto Maintenance Practice Questions and Study Guide

Brake fluid is specifically designed to operate under high-pressure conditions and at varying temperatures to ensure the effective functioning of the vehicle's braking system. The most common types of brake fluid used in vehicles are DOT 3, DOT 4, and DOT 5.1. These designations refer to standards set by the Department of Transportation, indicating the fluid's boiling point, viscosity, and compatibility.

DOT 3 fluid is glycol-based and absorbs moisture over time, which can lower its boiling point. DOT 4 also has a glycol base but typically has a higher boiling point due to the addition of borate esters, making it more suitable for heavier braking situations. DOT 5.1 is also glycol-based but is designed to provide better performance under extreme conditions and is compatible with DOT 3 and DOT 4 fluids.

In contrast, ATF fluid is primarily used in automatic transmissions, and hydraulic fluid, while it could refer to the broader category including brake fluid, is not specific enough as a type. Engine oil is entirely unrelated to braking systems. Therefore, understanding the specific types of brake fluid and their applications is crucial for vehicle maintenance and safety, making DOT 3, DOT 4, and DOT 5.1 the correct choice for