DOT 4
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:
| 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) |
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 |