Brake Fluid vs. Automatic Transmission Fluids (ATF)
Comparing 2 standards across 14 specifications. 14 key differences identified.
DOT Brake Fluid (standardized under US FMVSS 116, SAE J1703/J1704, and ISO 4925) defines the hydraulic fluid specifications for automotive braking systems. Governing Dry Boiling Points (fresh fluid) and Wet Boiling Points (3.7% water contamination absorbed over time) across glycol-ether fluids (DOT 3, DOT 4, DOT 5.1) and silicone-based fluid (DOT 5).
Automatic transmission fluids (ATF) are highly engineered multi-functional hydraulic fluids standardized by OEM specifications (GM Dexron VI, Ford Mercon LV, Chrysler ATF+4, Toyota WS, ZF Lifeguard) into stepped planetary, Continuously Variable (CVT), and Dual-Clutch (DCT) fluid formulations with strict kinematic viscosities and friction-modifier curves.
Specification Comparison Table
14 Parameters| Parameter / Spec | ||
|---|---|---|
|
Standardization
|
FMVSS 116 / SAE J1703 (DOT 3), SAE J1704 (DOT 4), ISO 4925 Class 3/4/6/7 | — |
|
DOT 3 Minimum Boiling Points
|
Dry: 205°C (401°F) | Wet (3.7% H₂O): 140°C (284°F) — Standard domestic vehicles | — |
|
DOT 4 Minimum Boiling Points
|
Dry: 230°C (446°F) | Wet: 155°C (311°F) — Modern European and Japanese passenger cars with ABS/ESP | — |
|
DOT 4 Class 6 (Low Viscosity)
|
Low viscosity at -40°C (max 750 mm²/s vs 1500 mm²/s standard) for rapid ABS/ESP active brake pulsing in freezing winters | — |
|
DOT 5.1 (High Performance Glycol)
|
Dry: 260°C (500°F) | Wet: 180°C (356°F) — Glycol-ether base compatible with DOT 3 and DOT 4 systems | — |
|
DOT 5 (Silicone-Based — Purple)
|
Dry: 260°C (500°F) | Hydrophobic silicone base (NEVER mix with DOT 3/4/5.1; used in classic cars and military Harley-Davidsons) | — |
|
Governing Standards
|
— | SAE J311 / GM GMN10060 (Dexron VI) / Ford WSS-M2C938-A (Mercon LV) / JASO 1-A-LV (Japanese OEM) |
|
GM Dexron VI
|
— | Viscosity: 5.83 cSt at 100°C | Fully backward compatible with Dexron II/III | Shear-stable synthetic |
|
Ford Mercon LV
|
— | Viscosity: 5.7 cSt at 100°C | Low-viscosity standard for modern 6-speed and 10-speed (10R80) transmissions |
|
Chrysler / Stellantis ATF+4
|
— | Viscosity: 7.3 cSt at 100°C | High shear-stability Group III synthetic | Mandatory for Torqueflite / 42RLE |
|
Toyota Genuine ATF WS
|
— | Viscosity: 5.4 cSt at 100°C | Low-viscosity 'World Standard' for Toyota/Lexus 6/8-speed automatic transmissions |
|
CVT Fluid (Push-Belt / Chain)
|
— | High metal-to-metal steel belt friction coefficients (NS-2/NS-3, Lineartronic) | NEVER mix with standard ATF |
|
Dual-Clutch Transmission (DCT/DSG)
|
— | Wet-clutch synchronization + high-pressure hydraulic valve bodies (VW G 052 182 / Pentosin FFL-2) |
|
Operating Temperature Limits
|
— | Optimal: 77°C–93°C (170°F–200°F) | Every 11°C (20°F) above 93°C halves fluid life via thermal oxidation |