DOT 3

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DOT 3 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 Standard No. 116; Motor vehicle brake fluids.[1] Under this standard there are four Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4, DOT 5 and DOT 5.1.

DOT 3, like DOT 4 and DOT 5.1, is a polyethylene glycol-based fluid (contrasted with DOT 5, which is silicone-based). Fluids such as DOT 3 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 concern in racecars or motorcycles[citation needed].

DOT3 has been all but replaced with the superior DOT4 as there is little cost difference between the two.

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 [2]
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 2 Brake fluids DOT 4

References[edit]

  1. ^ Code of Federal Regulations, Title 49 - Transportation, Chapter V - Part 571 - Federal Motor Vehicle Safety Standards (49CFR571), Subpart B, Sec. 571.116 Standard No. 116; Motor vehicle brake fluids
  2. ^ FMVSS 116 - Brake Fluid Standards