DOT 3 vs DOT 4 Brake Fluid – A Comparison

One of the most mundane aspects of being a car owner is having to maintain it. We all know that a car should have a regular checkup including things such as your air filter and oil changes. Besides that, though, it’s not enough to just take it in to a mechanic whenever something out of the ordinary happens. There are also many vital fluids that will need to be replaced regularly. One of these is brake fluid.

Did you know that there were several different types of brake fluids? Probably not and that’s okay. Brake fluid is one of those necessary items your vehicle requires as its main function is to allow your brake lever to transmit and create pressure to the pads on your brakes, which is what allows your vehicle to stop.

What Does the DOT In DOT 3 and DOT 4 Mean?

There are many different types of brake fluids. In this article we will discuss the two most common types, which are DOT 3 and DOT 4. The DOT refers to simply refers to the Department of Transportation. You will be happy to know that brake fluids must meet specific standards that are set by that department before they are allowed to be let into the market. This helps to ensure that you’re not putting complete junk in your car that may be harmful or ineffective.

There are four tests that the brake fluids must pass in order to get the stamp of approval from the Department of Transportation. All DOT brake fluids must:

• Be able to remain fluid at low temperatures and not solidify or freeze
• Resist boiling at high temperatures
• Be able to cooperate with the other parts of the braking system
• Fight against corrosion throughout the entire braking system

As you can see, there are rigorous tests and standards that any brake fluid must meet. Therefore, if the brake fluid has “DOT” on the bottle it has met any and all requirements that have been established by the Department of Transportation and the National Highway Safety Administration.

Understanding Your Brake Fluid

It’s important to realize that the purpose of brake fluid is to be exposed to high heat levels. The reason for this is because when the brake lever and brake pads come together to stop your vehicle (when you hit your brakes) it creates kinetic energy, which is then converted into heat.

These brake fluids are comprised of many different ingredients. The main differences between them lie in what ingredients are used in it and its boiling point. The higher the DOT number, the higher the heat resistance (or boiling point) will be. The brake fluid begins to vaporize once it’s reached its boiling point which is why this is important to know when referring to brake fluids in general.

When it comes to brake fluid, there are two different boiling points to become familiar with and consider. There is a dry boiling point as well as a wet boiling point, and it’s important to understand the difference. Generally speaking, the wet boiling point should be lower than the brake fluid’s dry boiling point.

Most brake fluids are hygroscopic, which means that they absorb water from the air and environment. So, when you see a reference to a “wet boiling point” this is simply referring to the boiling point of your brake fluid after it’s absorbed X amount of moisture.

You don’t want to get hung up on this too much as the formulations required to figure out the wet boiling point are pretty complicated, so mainly just focus on the dry boiling point temperature and you should be fine.

Both DOT 3 and DOT 4 brake fluids are primarily made from a poly-glycol base. They will both include:

• Inhibitors which help to prevent corrosion,
• A modifier-coupler which will help reduce the swelling of rubber parts it comes into contact with,
• A solvent diluent which is what determines the boiling point of the brake fluid and makes up about 50 to 80% of the brake fluid itself, and lastly
• A lubricant which is what will allow the parts to move freely and makes up about 20 to 40% of the brake fluid.

Now that you have a basic understanding of what brake fluid is and why it’s important let’s move on to the differences between DOT 3 brake fluid and DOT 4 brake fluid.

DOT 3 Brake Fluid

DOT 3 brake fluid is fully synthetic and is comprised of a petroleum/non-mineral-based and non-silicone fluid. It is basically created by mixing both glycerin and alcohol. This type of brake fluid has high boiling points and is known to allow for consistent performance for drivers that tend to brake frequently. DOT 3 brake fluid can withstand a temperature of just over 205°C, which is up to 400°F, before hitting its dry boiling point.

If you need to quickly top off your brake fluid this is probably the brake fluid you should go for. It’s especially good for those that drive heavy duty vehicles, four-wheel drive vehicles, non-European passenger cars, and even motorcycles. Also, if you’re one of those car owners that referred to the manual for every requirement and find that no exact brake fluid is mentioned, this is the one you should use.

Also, DOT 3 brake fluid is often an amber colored liquid and should be changed every 3 to 5 years, although some mechanics recommend changing your brake fluid every other year just to be safe. Making sure to stay up to date with the brake system’s maintenance will help improve the effectiveness of any and all fluids and parts involved. This will ensure that you keep your car happy and healthy for the long ride.

DOT 4 Brake Fluid

DOT 4 brake fluid is usually a glycol ether-based fluid that oftentimes includes borate esters. The combination of these ingredients is designed to help boost your vehicle’s brake’s performance. The borate esters specifically target improvement of the dry and wet boiling points of your brake fluid, so DOT 4 brake fluid automatically comes with the ability to deal with a higher temperature.

DOT 4 brake fluid can typically withstand a dry boiling point temperature of 230°C, or about 450°F and a wet boiling point temperature of 155°C, which is just over 300°F. DOT 4 brake fluid is typically what car racers use in their automobiles.

Generally speaking, though, DOT 4 brake fluid should only be used if your car’s manual indicates so or if you are driving a European vehicle. DOT 4 brake fluid is known to absorb more water faster than DOT 3 and it is generally a blue color rather than an amber hue like the DOT 3 brake fluid. That’s also a good way to tell the difference between the two.

Is There A Difference In Schedule Between Both Brake Fluids?

Another thing to consider should you find that you should be using the DOT 4, is that this one requires that you change it more frequently. It should be changed every two years, which is more than the DOT 3 brake fluid. This just means that there will be a little more maintenance involved if you decide to use this type of brake fluid.

Don’t worry if you haven’t kept up with it on an exact schedule. As with any neglect to a vehicle, not changing your brake fluid often enough can surely result in unsafe conditions, but when it comes to the brakes the damage doesn’t usually happen overnight. It’s more of a gradual process.

Now, since both DOT 3 and DOT 4 brake fluid are hygroscopic (meaning they absorb water), the water absorbed can lead to corrosion of the metal parts in your car that it comes into contact with and can also cause your brakes to become “spongy” and unreliable. Obviously, that’s not good. So, if it’s been a while (or never) since you’ve had it changed, it’s probably time to do so.

No matter what brake fluid you decide to go with you will want to pick a brake fluid that will be able to perform its necessary tasks. These tasks include keeping your calipers lubricated, preventing corrosion to the various metal parts and pieces it may come into contact with, and also be able to exhibit a high boiling point.

If you’re still unsure which brake fluid to go with when it comes to DOT 3 vs DOT 4 brake fluid and want to avoid a trip to the mechanic, the general rule is to go with DOT 3 (unless it’s a European car, our best brake fluid for BMW guide goes into detail about DOT 4 brake fluids for BMW). The differences between the two are not huge and DOT 3 is usually more commonly used one with far less maintenance required.

As an aside, if you are flushing your brake fluid yourself, make sure to handle it with care. No matter which one you’re using, the fluid is very corrosive. So, if you spill it on your paint or any of the other metal components in your car and even your skin it can be extremely harmful. You will want to wear gloves and eye protection just to be safe and make sure to wash your hands thoroughly as soon as you’re finished.