DOT 4 is the most commonly specified brake fluid for modern vehicles, offering higher boiling points and a greater safety margin than DOT 3. Its improved stability under heat makes it suitable for both factory fill and aftermarket use. DOT 4 remains fully compatible with DOT 3. Minimum dry boiling point 230°C/446°F, minimum wet boiling point 155°C/311°F, maximum viscosity 1500 cSt at –40°C.