Difference Between DOT 3 And DOT 4: A Complete Guide

One of these crucial components is the brake system because you want it to work correctly in an emergency. One of these items that need to be replaced every one to two years is brake fluid; otherwise, it may lead to rust inside the brake system and harm other parts.

The two main categories of braking fluids produced are silicone-based and glycol-based. For many cars, the widely used glycol-based braking fluids DOT 3 and DOT 4 are readily accessible. Average drivers prefer DOT 3, while DOT 4 is more prevalent in recent automobile models.

What distinguishes them from one another, and can you combine them?

DOT 3 vs. DOT 4 Brake Fluid Differences

The primary distinction between DOT 3 and DOT 4 brake fluid is better suited for enhanced performance because it has a higher wet and dry boiling point.

The type most frequently found in modern cars and trucks is DOT 3. However, DOT 4 is becoming more well-liked due to the growing usage of traction control and anti-lock braking systems, both of which profit from DOT 4 fluid’s lower viscosity. Glycol-based chemicals called DOT 3 and DOT 4 brake fluids are used in your braking system.

Due to their hygroscopic nature and ability to collect water from the air, caution must be used when storing and routinely replenishing possibly contaminated fluids.

Can You Mix DOT 3 And DOT 4 Brake Fluid?

It is possible to combine DOT 3 and DOT 4 brake fluid. They are compatible with one another because they are both glycol-based brake fluids. Although it’s OK to load your automobile with DOT 3 if it already has DOT 4, it’s not advised if it came with DOT 4.

Adding brake fluid in the reservoir.

If the factory installed DOT 3 in your vehicle and you frequently tow a trailer or drive up steep slopes, we strongly advise replacing it with DOT 4.

DOT 3 Vs. DOT 4: Which One Is The Better Brake Fluid?

DOT 3 is more widely used than the two brake fluids, but DOT 4 is swiftly catching on thanks to its compatibility with the industry-standard traction control and anti-lock braking system.

DOT 4 is preferable for all applications due to its higher boiling temperatures; although it is frequently slightly more expensive, buying it is worthwhile.

What Happens If You Use DOT 3 Instead Of DOT 4 Brake Fluid?

While DOT 3 brake fluid can be used in place of DOT 4, doing so is not advised. Since both of these fluids are glycol-based, moving between them won’t cause any harm to the parts of the brake system.

However, DOT 3 brake fluid has a lower boiling point than DOT 4 brake fluid, which could be problematic in heavy-duty situations like towing or going up steep hills. As a general rule, you should always use brake fluid manufactured to the exact specifications of your cars.

What Happens If You Use The Wrong DOT Brake Fluid?

The type of braking fluids you have combined will determine this. Nothing extraordinary will occur in the case of DOT 3 and DOT 4 other than a change in boiling point.

Because DOT 3 has a lower boiling point than DOT 4, it can cause the brakes of a DOT 4-based brake system to fade more quickly when stopped by large loads. And you don’t want that when you’re heading downward.

White Jeep SUV cruising downhill.

Furthermore, these brake fluids are glycol-based and cannot be mixed with the silicone-based DOT5 version, a more recent formulation.

How Often Should You Change DOT 4 Brake Fluid?

The DOT 4 brake fluid should be changed at least every two years. If you routinely drive up and down steep mountain roads or use your car for heavy-duty tasks like towing a trailer, you may need to do it more frequently.

This is so that it can collect moisture from the air due to the DOT 4 brake fluid’s hygroscopicity. When subjected to heavy loads, this moisture may develop into steam, evaporate, and produce air locks that reduce the brakes’ effectiveness.

How Do I Know Which Brake Fluid To Use?

You can always consult the owner’s manual to learn which brake fluid is suggested for your particular car. Or in some circumstances, this is also written on the cover of the brake fluid reservoir, located someplace close to the brake booster.

Anyhow, changing from DOT 3 to DOT 4 fluid is brilliant because it raises the boiling point and strengthens the brake system’s resistance to heavy loads. However, it is advised to do it in a different way around.


These days, DOT 3 or DOT 4 brake fluid is used in most automobiles. These two fluids are essentially the same because they both contain glycol. Their boiling point, which is higher for DOT 4, is the only distinction.

As a result, DOT 4 brake fluid is better suited for demanding applications involving a lot of forceful brakings, such as when pulling a trailer. However, since DOT 5 brake fluid is silicon-based, neither should be used with it.

These will only combine appropriately because of their different chemical structures. The hydraulic properties of DOT 3 and DOT 4 braking fluids are also impacted by the airborne moisture they absorb. They must therefore be replaced every two years for this reason.

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About Brock Rangel

Hi, I am Brock, and I am the lead editor/photographer for TheCarColony. I have been a mechanic for over 14 years now, and I am here to spread my car knowledge across the web!

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