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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.

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™ 3000.

 

 

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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™ 3000.
Kin. vis. yes
Dyn. vis. no
Density no
Multiple temperatures yes
Keywords Brake fluid, hydraulic fluid, LHM, kinematic viscosity, SVM™ 3000, SAE, FMVSS No. 116

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