DOT 4

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DOT 4 is one of several designations of automotive 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 4, like DOT 3 and DOT 5.1, is a polyethylene glycol-based fluid (contrasted with DOT 5 which is silicone-based). Fluids such as DOT 4 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 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 ( 376°F)

[edit] Ingredients

One particular brand of DOT 4 brake fluid lists the following ingredients on its MSDS:

Chemical	CAS no	Percent
Triethylene glycol	000112-27-6	5-25
Tetraethylene glycol	000112-60-7	5-25
Dibutoxy tetraglycol	000112-98-1	10-50
Tetraethylene glycol diethyl ether	004353-28-0	10-50
Propane, 2-methoxy-1-(2-methoxy-1-methylethoxy)-	089399-28-0	10-50