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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 Standard No. 116; Motor vehicle brake fluids.[1] 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, which is necessary to prevent sheer and undiluted water in the braking system,[citation needed] which is very corrosive, also water droplets can freeze in the pipes, thus blocking the system.

DOT 5.1 is the non-silicone version of DOT 5, defined by FMVSS 116 as being less than 70% silicone. Above that threshold makes it DOT 5.

Boiling points

Minimum 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 5 Brake fluids None

Maximum Viscosity

Maximum viscosity

Maximum viscosity ranges [3]
Maximum Viscosity {cst = centistokes} Viscosity limit
DOT 3 -40°C°F 1500cst
DOT 4 -40°C°F 1800cst
DOT 5 -40°C°F 900cst
DOT 5.1 -40°C°F 900cst


References

  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
  3. ^ FMVSS 116


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