Brake fluid DOT3 and DOT4 are the two most widely used hydraulic brake fluids in passenger cars and commercial vehicles. Both are glycol-based fluids that transmit braking force from the pedal to the calipers, but they differ in boiling point and performance class. This buying guide explains the differences, the standards and what to check when sourcing.
DOT3 vs DOT4: What Is the Difference?
Both DOT3 and DOT4 are non-petroleum fluids based on glycols, glycol ethers and corrosion inhibitors. The critical difference is the dry and wet equilibrium reflux boiling point (ERBP):
| Property | DOT3 | DOT4 |
|---|---|---|
| Dry ERBP | ≥ 230 deg C | ≥ 263 deg C |
| Wet ERBP | ≥ 158 deg C | ≥ 166 deg C |
| Viscosity at -40 deg C | ≤ 1500 mm2/s | ≤ 1800 mm2/s |
| Typical use | Standard braking systems | ABS, high-performance and heavy braking |
DOT4 absorbs the higher-temperature duty because modern ABS and traction control systems generate more heat in the fluid. Standards: FMVSS No.116 DOT3/DOT4, ISO 4925 Class 3, GB 12981-2012 (HZY3/HZY4).
Why Boiling Point Matters
Brake fluid is hygroscopic – it absorbs moisture from the air over time. Water lowers the boiling point dramatically (the wet ERBP), and if the fluid boils under hard braking, vapour bubbles compress instead of transmitting force – brake fade. That is why wet ERBP is the real-world safety number and why high-quality inhibitors and glycol chemistry matter.
What to Check When Buying Brake Fluid
- Specification compliance: verify against FMVSS 116, ISO 4925 and the local standard (e.g. GB 12981-2012).
- Corrosion protection: the fluid must protect the seven metals in the braking system – steel, cast iron, aluminum, brass, copper, zinc and tinned iron.
- Rubber compatibility: seals (SBR, EPDM) must not swell or harden excessively.
- Batch documentation: request the full test report: ERBP, wet ERBP, viscosity at -40 deg C and corrosion results.
Source DOT3/DOT4 From Minglan
Shanghai Minglan Chemical produces high-quality DOT3 and DOT4 brake fluids meeting GB 12981-2012, FMVSS No.116 and ISO 4925, with full quality control on boiling point, viscosity and corrosion performance. Contact info@minglanchem.com for specifications, samples and pricing.
