A bit of brake fluid triva

Lets look at what the DOT ratings mean. The table below shows the MINIMUM wet and dry boiling points for DOT 2, 3, 4, and 5 brake fluid in degrees fahrenheit.

DOT 2-Dry Boiling point 374

DOT 3-Dry Boiling point 401 Wet boiling point 284

DOT 4-Dry Boiling point 446 Wet boiling point 311

DOT 5-Dry Boiling point 500 Wet boiling point 356

The DOT 2 spec is for drum brakes and is obsolete. If you have any DOT 2 in your garage, throw it away! DOT 5 is for silicone brake fluid. Silicone brake fluid (DOT 5) should be avoided because it is not compatible with regular brake fluid, it is hard to pour without introducing bubbles and thus results in soft pedal feel, and moisture still gets into your system and will pool in low areas like your calipers and encourage rapid corrosion. STAY AWAY!

That leaves DOT 3 and DOT 4 fluids. These fluids are compatible with each other and may be interchanged or mixed with no ill effects.