DOT 4 vs DOT 5.1 Brake Fluid: What's the Difference?

DOT 4 vs DOT 5.1 Brake Fluid: What's the Difference? main image DOT 4 vs DOT 5.1 Brake Fluid: What's the Difference? image

Quick Facts

  • Both are glycol-based and mixable

  • DOT 5.1 resists heat better than DOT 4

  • DOT 5 (not "5.1") is silicone-based – not compatible

  • Switching to DOT 5.1 may improve brake performance

  • Always check your service manual to what's recommended for your machine

When it comes to brake fluid, DOT 4 and DOT 5.1 are two commonly used types—especially in cars, motorcycles, and bicycles. Both are glycol-based, meaning they’re chemically similar and compatible, but they perform differently under pressure.

Key Difference: Boiling Point

The main distinction between DOT 4 and DOT 5.1 is their boiling points—important for maintaining braking performance during heavy use.

Fluid Type Dry Boiling Point Wet Boiling Point
DOT 4 ~230°C ~155°C
DOT 5.1 ~260°C ~180°C

DOT 5.1 handles heat better, making it more suitable for high-performance or prolonged braking conditions.

Which Should You Use?

  • Use DOT 4 for everyday riding or driving

  • Upgrade to DOT 5.1 for racing and heavy braking conditions

Bottom Line

DOT 4 and DOT 5.1 are compatible but not identical. If your brakes face extreme conditions, DOT 5.1 is worth the upgrade. Just steer clear of DOT 5, which isn’t compatible with either.