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CATEGORIES (articles) > Steering, Suspension, brakes & drivetrain > Brakes > DOT 4 Brake fluid

DOT 4 Brake fluid

DOT 4 is one of several designations of brake fluid denoting a particular mixture of chemicals imparting specified ranges of boiling point.

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 performance of the fluid 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.

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)


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

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CATEGORIES (articles) > Steering, Suspension, brakes & drivetrain > Brakes > DOT 4 Brake fluid

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