What does DOT4 mean?

[NathanLynn]

DOT4 is a specification grade for automotive brake fluid. Here are the relevant details: 1. Replacement interval: Since brake fluid is alcohol-based, it has strong hygroscopic properties. Over time, its water content gradually increases. After about 12 months of use, DOT3 and DOT4 brake fluids typically contain an average of 3% water content. When brake fluid contains excessive moisture, it can cause delayed braking response and extended stopping distances. Therefore, it is recommended to replace the brake fluid every 2 years (or 40,000 kilometers). 2. Mixing compatibility: Qualified brake fluids of the same quality grade can be mixed. For example, DOT4 brake fluids from major brands can be mixed. However, if the vehicle originally uses low-quality DOT3 brake fluid and is being upgraded to high-quality DOT4, the original brake fluid must be completely drained first.

[Will]

Dot4 is a specification of brake fluid, one of the standards established by the U.S. Department of Transportation. I think Dot4 is particularly important in daily car maintenance because it has a higher boiling point—wet boiling point of at least 155°C and dry boiling point above 230°C, significantly better than the older Dot3. This means that during long-distance driving or downhill mountain roads, the brakes are less likely to overheat and fail, ensuring safety. I always remind car owners to regularly check the brake fluid reservoir; as long as the fluid level is between min and max, and the color is clear without turning black, it's fine. If it becomes cloudy or hasn't been changed for two years, the absorbed moisture lowers the boiling point, which can lead to a spongy brake pedal—a dangerous situation. Replacing Dot4 isn’t expensive, but neglecting it could cost a fortune to repair the entire braking system. It’s especially useful for modern cars with higher engine temperatures, as Dot4 is more heat-resistant. I’ve seen too many cases where careless owners nearly caused accidents due to brake failure, so I emphasize this detail during every maintenance check.

[JulietteDella]

As a family driver, Dot4 is a must-have type of brake fluid for me. Driving the kids to school, safety is the top priority, and Dot4's high boiling point makes the brakes more reliable in hot weather. I've developed the habit of checking the fluid level every 20,000 kilometers, topping it up a bit if it's too low, but never mixing different types. Compared to Dot3, Dot4 is less prone to absorbing moisture and deteriorating, saving both money and hassle. Once, I neglected to change it, and the fluid turned black, causing sluggish brake response, which scared me into getting it fixed immediately. Now I've learned to do a simple test myself: open the can when the engine is cold, use a test strip to check for moisture, and replace it if it exceeds 3%. Remember to buy from reputable brands—counterfeit products can be dangerous. For ordinary cars, Dot4 is the standard choice; don't opt for inferior products just to save a few bucks.

[Gabriela]

Dot4 is essentially the standard designation for brake fluid. From a chemical perspective, I appreciate that it's based on glycol ether compounds with strong hygroscopic properties—meaning it absorbs moisture from the air, which lowers its boiling point. This is precisely why regular replacement is mandatory: more moisture means weaker braking performance. Dot4 has a wet boiling point of 155°C and a dry boiling point of 230°C, outperforming Dot3 but falling short of silicon-based Dot5. However, Dot5 isn't compatible with most vehicles. As an automotive enthusiast, I've researched the history of DOT standards—they've enhanced safety since 1968. When choosing Dot4, prioritize higher boiling point values. Its hygroscopic nature makes maintenance critical; it's easily overlooked in daily driving but carries severe consequences. Remember, avoid prolonged exposure to air to prevent accelerated degradation.