Brake Fluid Classification
The U.S. Department of Transportation (DOT) classifies brake fluids into four major classes: DOT 3, DOT 4, DOT 5, and DOT 5.1.
FMVSS (Federal Motor Vehicle Safety Standards) #116 defines the properties that must be met in order for a brake fluid to be classified in one of the DOT categories.
The table below shows some of the restrictions that brake fluid must meet under FMVSS 116, International Standard ISO 4925 and SAE (Society of Automotive Engineers) classes.
Brake fluid classes
| SAE and ISO Standarts |
SAE J 1703 | ISO 4925 Class 3 | SAE J 1704 | ISO 4925 Class 4 | ISO 4925 Class 6 | SAE J 1705 | ISO 4925 Class 5.1 |
| FMVSS 116 | DOT 3 | DOT 4 | DOT 5 | DOT 5.1 | |||
| Dry boiling point, °С | ≥ 205 | ≥ 205 | ≥ 230 | ≥ 230 | ≥ 260 | ≥ 250 | ≥ 260 |
| Wet boiling point, °С | ≥ 140 | ≥ 140 | ≥ 155 | ≥ 155 | ≥ 180 | ≥ 165 | ≥ 180 |
| Viscosity, mm2/s at ‑40 °С | ≤ 1800 | ≤ 1500 | ≤ 1800 | ≤ 1500 | ≤ 900 | ≤ 750 | ≤ 900 |
Use of brake fluids
| Labeling | Description |
| DOT 3 | Designed for vehicles with a hydraulic drive system with drum and disc type brakes. |
| DOT 4 | Used for vehicles with disc brakes on both axles, including those equipped with ABS. |
| DOT 5 | These are silicone-based fluids that have increased performance characteristics. They are used for vehicles with frequent acceleration and prolonged braking. |
| DOT 5.1 | Used for vehicles with significant high-temperature loads, such as sports cars. |