DOT 5.1

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

A brake fluid's dry boiling point is the temperature at which the pure fluid will boil. Wet boiling point concerns the boiling temperature when the fluid contains water.

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). Polyethylene glycol fluids are hygroscopic and will absorb water from the atmosphere. This degrades the fluid's performance, and if allowed to accumulate over a period of time, can drastically reduce its dry boiling point. In a passenger car this is not much of an issue^{[citation needed]}, but can be of serious concerns in racecars or motorcycles^{[citation needed]}.

As of 2006, most cars produced in the U.S. use DOT 3 brake fluid.

[edit] Boiling points

Minimal boiling points for these specifications are as follows:

Boiling point ranges

	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 5	Brake fluids			None