Technical Articles
Brake Literature
Understanding BRAKE FLUIDS
The higher the DOT number, the higher the brake fluid performance ?
This is not exactly correct. The DOT numbers categorizes the fluids by various uses.
| Specification | Application use |
|---|---|
| DOT3 | Cars with small to medium sized engines |
| DOT4 | Cars with larger sized engine and/or for use with sports driving |
| DOT5.1 | Cars with larger sized engine and/or for use with sports driving Cars with larger sized engine and/or for use with sports driving (Cold climate regions) |
| DOT5 | Main ingredient is Silicon, Special application cars (Hummer, Harley-Davidson) |
| Major difference | DOT3 vs DOT4 | Boiling point temperature |
|---|---|---|
| DOT4 vs DOT5.1 | Boiling point temperature & viscosity at low temperatures |
DOT 5.1 has strict viscosity standards at lower temperature in addition to having a high boiling point temperature. Therefore, in cold climate areas, the DOT 5.1 brake fluid is very commonly used on most cars. The most widely distributed brake fluid is the DOT 4, which has a dry boiling point temperature around 270℃ and a wet boiling point temperature around 170℃.The boiling point temperatures of DOT4 is very similar to those of DOT5.1. The major difference is the viscosity at low temperatures.
Today, cars are commonly equipped with ABS, and DOT5.1 fluid is used since the viscosity of it helps the ABS work consistently even in cold climates.