Viscosity of Automotive Brake Fluids
Hydraulic fluids for brake and clutch systems in civil and military road vehicles.
Description
Automotive brake fluids are mainly used in the brake and clutch systems of road vehicles. They transmit the pressure applied on the master brake cylinder via the brake pedal to the wheel brake cylinders of road vehicles. Brake fluids used in hydraulically operated clutches transmit the pressure applied on the master cylinder to the slave cylinder of the clutch system.
Viscosity is an essential parameter for the safety of a road vehicle as it directly influences the operation and behavior of the brake system and/or the clutch. Therefore, these liquids must fulfill specifications mainly at -40 °C and +100 °C, liquids used for military purposes at -55 °C and + 100 °C. Most producers also state values at + 40 °C and give the viscosity index. There are three main types of brake fluids which are classified by their different chemical base:
- polyglycolether / borate ester - DOT 3, DOT 4 types, DOT 5.1 types (the main difference between these three types is - simply put - a different ratio of glycol and borate ester and the amount of additives)
- silicone oil - DOT 5 types
- mineral oil - LHM
This is the reason why they do not mix with each other.
Viscosity Tables – Measurement data
DOT 3 (SAE J1703, FMVSS No. 116, ISO 4925 – Class 3)
| Temp. [°C] | Kin. Viscosity [mm²/s] Specified |
|---|---|
| -40 | max. 1500 |
| 100 | min. 1.5 |
DOT 4 (SAE J1704, FMVSS No. 116, ISO 4925 – Class 4)
| Temp. [°C] | Kin. Viscosity [mm²/s] Specified | Kin. Viscosity [mm²/s] Measured |
|---|---|---|
| -40 | max. 1800 | 1121.24 |
| 100 | min. 1.5 | 2.1369 |
DOT 4+, Super DOT4 (ISO 4925 - Class 6)
| Temp. [°C] | Kin. Viscosity [mm²/s] Specified | Kin. Viscosity [mm²/s] measured |
|---|---|---|
| -40 | max. 750 | 717.55 |
| 100 | min. 1.5 | 2.1119 |
DOT 5.1 (FMVSS No. 116, ISO 4925 - Class 5-1)
| Temp. [°C] | Kin. Viscosity [mm²/s] Specified | Kin. Viscosity [mm²/s] Measured |
|---|---|---|
| -40 | max. 900 | 717.71 |
| 100 | min. 1.5 | 2.1419 |
DOT 5.1 ESP (FMVSS No. 116, ISO 4925 - Class 6)
| Temp. [°C] | Kin. Viscosity [mm²/s] Specified |
|---|---|
| -40 | max. 750 |
| 100 | min. 1.5 |
DOT 5 (SAE J1705, FMVSS No. 116)
| Temp. [°C] | Kin. Viscosity [mm²/s] Specified |
|---|---|
| -40 | max. 900 |
| 100 | min. 1.5 |
DOT 5 (MIL-PRF-46176)
| Temp. [°C] | Kin. Viscosity [mm²/s] Specified |
|---|---|
| -55 | max. 900 |
| 100 | min. 1.3 |
LHM (PSA B-712710)
| Temp. [°C] | Kin. Viscosity [mm²/s] Specified | Kin. Viscosity [mm²/s] Measured |
|---|---|---|
| -40 | 1000 - 1200 | 1069.64 |
| 100 | 6 - 6.5 | 6.2514 |
Reference
DOT specifications in SAE standards J 1703, J1704 and J1705, FMVSS No. 116, ISO 4925, MIL-PRF-46176, PSA B-712710, measurement with SVM™.
Metainformation
| Reference | DOT specifications in SAE standards J 1703, J1704 and J1705, FMVSS No. 116, ISO 4925, MIL-PRF-46176, PSA B-712710, measurement with SVM™. |
|---|---|
| Kin. vis. | yes |
| Dyn. vis. | no |
| Density | no |
| Multiple temperatures | yes |
| Related | Brake fluid, hydraulic fluid, LHM, kinematic viscosity, SVM™, SAE, FMVSS No. 116 |