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DOT 5 is one of several North American designations of automotive hydraulic brake fluid, denoting a particular mixture of chemicals imparting specified ranges of boiling point.

DOT 5 is a silicone-based brake fluid (contains at least 70% by weight of a diorgano polysiloxane[1]).

Unlike polyethylene glycol based fluids, Dot 5 is hydrophobic.[2] An advantage over other forms of brake fluid is that silicone has a more stable viscosity index over a wider temperature range. Another property is that it does not damage paint.[citation needed]

DOT 5 brake fluid is not compatible with anti-lock braking systems. DOT 5 fluid can aerate when the anti-lock brake system is activated. DOT 5 brake fluid absorbs a small amount of air requiring care when bleeding the system of air.[3]

Boiling points[edit]

Minimal boiling points for these specifications are as follows (wet boiling point defined as 3.7% water by volume):

Boiling point ranges [4]
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 5.1 260 °C (500 °F) 180 °C (356 °F)
DOT 4 Brake fluids DOT 5.1