DOT 5.1

DOT 5.1 is one of several designations of brake fluid denoting a particular mixture of chemicals imparting specified ranges of boiling point.

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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 5.1, like DOT 3 and DOT 4, is a polyethylene glycol-based fluid (contrasted with DOT 5 which is silicone-based). Fluids such as DOT 5.1 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: