DOT 3 is one of several designations of brake fluid denoting a particular mixture of chemicals imparting specified ranges of boiling point.
In the United States, all brake fluids must meet federal standard #116. Under this standard there are three Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4, and DOT 5.1.
DOT 3, like DOT 4 and DOT 5.1, is a polyethylene glycol-based fluid (contrasted with DOT 5 which is silicone-based). Fluids such as DOT 3 are hygroscopic and will absorb water from the atmosphere. This degrades the fluid’s performance by drastically reducing its boiling point. In a passenger car this is not much of an issue, but can be of serious concerns in racecars or motorcycles.
As of 2006, most cars produced in the U.S. use DOT 3 brake fluid.
Boiling points
Minimal boiling points for these specifications are as follows:
| Dry boiling point | Wet boiling point | |
|---|---|---|
| DOT 3 | 205°C (401°F) | 140°C (284°F) |
| DOT 4 | 230°C (446°F) | 155°C (311°F) |
| DOT 5 | 260°C (500°F) | 180°C (356°F) |
| DOT 5.1 | 270°C (518°F) | 191°C (375°F) |
| DOT 2 | Brake fluids | DOT 4 | ||
|---|---|---|---|---|
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