Can I mix different grades of brake fluids?

Brake fluids DOT 3 brake fluids, 4 brake fluids and 5.1 brake fluids can be completely mixed with other brake fluids which belong to the same category, because DOT standards contain a test of compatibility.

But mixing a brake fluid with a high boiling point with a fluid having a low boiling point results into a fluid with properties and performances reduced compared to the superior performance of brake fluid.