Our car’s brakes are undeniably one of the most important parts of our car. It’s what helps us stay out of accidents and get where we need to go safely. That being said, it’s important to take care of our breaks regularly, and one of the elements to consider is brake fluid. If you’re not changing your brake fluid or using quality brake fluid, then you’re destined for a pair of sub par brakes that might not get the job done correctly.
So, what is quality brake fluid? Quality brake fluid should be hygroscopic (meaning it absorbs moisture), be able to resist compression, and have a high heat tolerance. These qualities will be found in DOT 3, DOT 4, and DOT 5.1, brake fluid options, but some vehicles can work with DOT 5 as well.
The Department of Transportation has given a variety of brake fluids options, naming them DOT 3, DOT 4, and DOT 5. Each of these have their own benefits, and choosing the right one for your car can be a challenge. We can help you make the right decision!
What is brake fluid?
Let’s start with the basics, because if you don’t know what brake fluid is, you will have a far more difficult time making a decision on which brake fluid is right for you and your car.
To put it simply, brake fluid is the fluid that is found inside of your brake lines. As your foot presses against the gas pedal, there’s an extreme amount of force that takes place. The brake fluid will push the force and transfer it into pressure that tightens up against the rotor. This process is what ultimately leads to the slowing down of your vehicle, and eventually stopping it altogether.
During the process there is a large amount of heat that is exerted from the brake discs and calipers. That is why it is so important for brake fluid to be resilient to high heat so it doesn’t boil. A brake fluid that can’t withstand high temperatures will virtually vaporize due to the intensity, rendering it useless. Luckily, companies know that brake fluid must be able to withstand high temperatures without boiling and be able to absorb moisture, and that’s where the Department of Transportation came up with DOT 3, DOT 4, DOT 5, and DOT 5.1.
What types of brake fluids are available?
Much like everything else in relation to cars, there’s a large variety of brake fluids available at auto parts store. This can make it somewhat of a challenge to find the brake fluid that’s right for you. Some of these brake fluids may cost less than 5 dollars, while others are upwards of 30. However, keep in mind that the more expensive brake fluids may not always mean better quality, especially if they are strictly designed for racing cars instead of regular cars.
The Department of Transportation has made things a little more simple for us to understand, creating brake fluids known as DOT 3, DOT 4, DOT 5, and DOT 5.1. All of these brake fluids adhere to the guidelines that brake fluid must have a very high boiling point, be flowable, and absorb moisture without vaporizing.
The difference between brake fluids is their boiling point. In the chart below, you will see the different boiling points of each brake fluid and what it is made out of.
| Name | Dry Boiling Point | Wet Boiling Point | Composition | Compatibility |
| DOT 3 | 401°F | 284° | Glycol Ether | DOT 4, DOT 5.1 |
| DOT 4 | 446° | 311° | Glycol Ether + Borate Ester | DOT 3, DOT 5.1 |
| DOT 5 | 500° | 356° | Silicone | None |
| DOT 5.1 | 500° | 356° | Glycol Ether + Borate Ester | DOT 3, DOT 4 |
*Dry boiling points refers to brake fluid that is brand new and has 0% water.
*Wet boiling points refers to the boiling point after the brake fluid has absorbed at least 3.7% of water.
As you can see, DOT 3 is the simplest brake fluid on the market. It’s made solely of glycol ester, as where DOT 4 and DOT 5.1 have added borate ester to increase their boiling points. You can mix DOT 3, DOT 4, and DOT 5.1, but it is extremely important to note that DOT 5 cannot be mixed with any other brake fluids as it is made with solely silicone. Trying to mix with other brake fluids can cause damage and may lead to brake failure.
How often should you change your brake fluid?
When it comes to car maintenance, there’s a lot to keep in mind. You want to make sure you’re oil is being changed regularly, that your brakes are in good working condition, your transmission is running properly, etc. But one thing that should never be overlooked is your brake fluid levels.
Since brake fluid is not a ‘big ticket item’ so to speak, it isn’t thought about as often as other parts of a car. However, not having enough brake fluid can lead to plenty of big-time problems, considering it’s the fluid that keeps your brakes functioning at the right level.
Making sure you check your brake fluid regularly is important. Some people will do it when they get their oil changed, which is an excellent idea, just to know where they are that. This doesn’t mean that you will need to change your brake fluid every time you perform an oil change, but it’s good to know where your levels are.
In reality, one should have their brake fluid topped off or switched out at least once a year. This will allow your car to have enough brake fluid to work properly and for your brakes to run smooth. However, if you are using DOT 4 brake fluid, you *may* want to have it changed a bit more frequently, perhaps twice a year. This is due to the fact that DOT 4 absorbs water quicker than DOT 3 brake fluid, and therefore can be used up before the one year mark.
Useful Information
A lot of vehicles will have the brake fluid needed inside of the manual. Check your car’s manual for the specific type of brake fluid that is required for your car. This will make the process far easier when trying to choose which brake fluid is right for you. However, remember that you can also top off or switch out between certain DOT brake fluids.
If you’re unsure about what type of brake fluid to get for your car, heading to your local auto parts store or your local mechanic can help you out. Asking a certified mechanic what their best suggestion is for your vehicle will help you to make the right decision.
Conclusion
With so many different brake fluid options on the market, it can be difficult to make the right choice. Just remember that a quality brake fluid will have viscosity, resilience to heat, and have the ability to absorb water. All of the DOT brake fluids have these essential qualities, and it will come down to your type of vehicle and personal preference on which one you decide to buy in the end.