The Difference Between DOT3 and DOT4 Brake Fluid

[AubreyAnn]

Brake fluids DOT3 and DOT4 have different compositions. Here is the relevant information: DOT3 Composition: Typically glycol-ether based, the chemical components of glycol-ether are polyethylene glycol or propylene glycol. Polyethylene glycol or propylene glycol have strong hydrophilic properties, so their water content gradually increases during use or storage. Since the boiling point of brake fluid decreases as water content increases, its braking performance declines accordingly. DOT4 Composition: Generally ester-based, ester-type brake fluids are made by adding a large amount of borate ester to the glycol-ether base. Borate ester is formed through the esterification reaction of polyethylene glycol or propylene glycol with boric acid. The boiling point of borate ester is higher than that of polyethylene glycol or propylene glycol, resulting in better braking performance.

[AniyahLee]

From practical driving experience, I usually use DOT3 brake fluid for regular family cars, but switch to DOT4 for performance vehicles. The key difference lies in high-temperature resistance. DOT4 has a boiling point 30-40°C higher than DOT3, with an even more significant gap in wet boiling points. During aggressive driving when brake system temperatures easily exceed 100°C, DOT4 is less prone to forming bubbles that cause brake fade. Another detail is that DOT4 absorbs moisture faster, requiring shorter replacement intervals. For daily commuting cars, DOT3 works fine, but if you frequently drive mountain roads or climb hills with heavy loads, DOT4 provides more peace of mind - after all, brakes aren't something to take lightly.