Your braking system is quite important. Your brake system’s functionality is the stopping power that allows you to slow down your vehicle to a stop whenever needed. Even in situations when a driver needs to quickly react, the brakes (when properly working) are your fail-safe to stop as quickly as possible to prevent any accidents. The brake fluid, which allows your brakes to work correctly, is an important part of the equation.
But does brake fluid expire? If you have a sealed bottle of brake fluid that has never been opened, your brake fluid has an infinite shelf life. An opened bottle is different, having a shelf life of about a year.
Brake fluid needs to stay at its graded boiling point, hence the reason for disposing of fluid that ends up retaining any moisture. An opened bottle will absorb moisture over time, which is detrimental to its effectiveness. Once it enters the fluid, the boiling point is brought down, therefore decreasing the fluid’s ability to perform its job. After a year, toss it. With the pressures that the braking system is creating, there is a ton of heat created through friction. The fluid needs to stay at that specific boiling point, so the brakes remain as effective as possible, and the brake pedal does not become spongy.
When to Dispose of Old Fluid
Brake fluid is a great item to have on-hand, but if the container ends up needing to have its seal broken to be used in your car, then the clock starts ticking. After we hit that year mark, it’s better to toss it than use it for your car. When your vehicle needs brake fluid, the fluid for your vehicle sits in a reservoir under the hood and is distributed through the brake lines to be used in the braking system.
Under normal circumstances, your brake fluid will not be consumed and does not evaporate; it’s only used over time as the brake pads wear. So, when the pads get replaced, the fluid gets topped off. If you have an unopened container, never hesitate to use it for your car as long as it is compatible fluid. But if you have an opened bottle that’s been shelved for an unknown period of time, it’s safer to just buy the new bottle.
As a side note, if your vehicle’s brake system seems like it may have a leak, this can be a serious issue and should be handled accordingly.
Types of Brake Fluid
Not all brake fluids are made alike. With the different types that exist, specific car manufacturers require that a brake fluid that is compatible with their cars be used. Some brake fluids absorb water, as mentioned, which hinders the functionality of the brake fluid. These types of fluids are glycol-based, and this gives them their water-absorbing properties.
Other types of brake fluid are silicon-based. When it comes to vintage cars and military vehicles, you are typically going to find silicone-based brake fluid in their system. The case for using this type of fluid in their systems is made by the fact that a silicone-based brake fluid will not corrode the inner workings of the brake system. It keeps the parts in the best shape possible. It also has the unique property of not damaging paint when it comes to those classic cars. Other types of brake fluid will eat the paint right off a car, so it’s understandable that silicon is the typical route with older cars.
Brake fluids are graded using the “DOT” system. DOT stands for the Department of Transportation, the entity that took it upon themselves to properly grade brake fluids to properly choose what is right for your car.
The number that follows the word DOT is used to grade that important boiling-point that we talked about. The higher the number, the higher the boiling point.
- DOT 3 Brake Fluid: DOT 3 is the most common type of brake fluid you will find in a typical vehicle that is used for conventional purposes. Although it is interchangeable with other brake fluids with a higher boiling point, if your vehicle is used for things such as getting to and from work, leisurely driving, getting from point A to B, then your car will most likely use DOT 3 fluid for its braking system.
- DOT 4 Brake Fluid: Having a higher boiling point and providing a better fluid for high-performance, DOT 4 is typically utilized in performance vehicles that require driving on the more aggressive side. It is considered the mid-graded boiling point in comparison to other brake fluids. If your vehicle is being used in a way that could be considered a step up from conventional driving, DOT 4 is an acceptable option. Even if your car recommends DOT 3 if you’re not quite sure which is better for your car, use DOT 4.
- DOT 5.1 Brake Fluid: This is the top boiling point when speaking in reference to glycol-based brake fluids. If you are doing a fair amount of aggressive driving, racing, dirt-track racing, off-roading, or drive a heavy-duty vehicle, then DOT 5.1 is the option for you. Especially when it comes to the heavy-duty applications that have any downhill driving. It is imperative to use a brake fluid with a higher boiling point because once that fluid hits the boiling point, it loses its ability to be effective.
- DOT 5 Brake Fluid: Being the one exception to the rest of the brake fluid options, DOT 5 is silicon-based. As mentioned, it is typically used in older, vintage vehicles and military vehicles. Other fluids absorb water, and since the machines that DOT 5 is used in tend to spend a lot of time sitting around without being used, the silicon base of DOT 5 will prevent any water from being absorbed. This utilizes the makeup of this fluid to prevent any corrosion over time, allowing the brake system to stay in sufficient shape, even when in storage.
Each fluid has its own, unique boiling point. That provides the grading we mentioned for each fluid and gives consumers the answer when choosing which fluid is right for their vehicle. Check out the chart below to become familiar with the different types of brake fluids, their dry boiling point, their wet boiling point, and their composition.
| Dry Boiling Point | Wet Boiling Point | Composition | |
| DOT 3 | 205°C/401°F | 140°C/284°F | Glycol ether |
| DOT 4 | 230°C/446°F | 155°C/311°F | Glycol ether |
| DOT 5.1 | 260°C/500°F | 180°C/356°F | Glycol ether |
| DOT 5 | 260°C/500°F | 180°C/356°F | Silicon |
The most important fact to note is the difference between DOT 5 and other applications. Due to its silicone base, DOT 5 cannot be interchanged with the other brake fluids. If it’s DOT 5, it will need to stay DOT 5 for the duration of the vehicle’s life.
What is Brake Fade?
A common term among car enthusiasts is “brake fade.” But what exactly does that mean and how can it affect your car? Boiling points have been a repeatedly referenced aspect of all brake fluids and for good reason. Once the fluid boils, the brake fluid is no longer as effective, leading to a braking system that is not as effective as it needs to be.
Brake fade is when gas (not gasoline) gets in the delivery lines for the brake fluid. This happens when your fluid hits that ever-so-important boiling point. Once the fluid boils, gas bubbles enter the lines, which then reach the moving parts of the brake system. Without a consistent flow of only fluid when the brakes are engaged, those air bubbles intermittently hit the braking parts and cause the brake pedal to become “spongy.” You will immediately recognize this while driving because the brake pedal will no longer have that tight, high-pressure feel when you step on the pedal.
Pump the Brakes
The correct brake fluid choice is imperative for your vehicle. Stop, take a moment to verify which fluid is best, and apply it to your brake system accordingly. If you are conflicted as to which choice is going to be best for your vehicle, choose the higher grade so long as you have a system with a glycol-based fluid. Using a higher graded fluid and then ending up not causing a higher level of brake heat is a much better option than going with a lower graded fluid that ends up boiling.
The brake system is always going to be one of the most important functions of any vehicle on the road. The fluid a driver chooses for their vehicle is just as important as any of the moving parts of the brakes. It is always best to choose the right option for your car when the need arises to pump those brakes.
Sources
“Understanding Brake Fluid Shelf Life and Other Important Auto Essentials”
Benjamin Hunting, November 4, 2016
“What Are the Different Types of Brake Fluid”
https://auto.howstuffworks.com/auto-parts/brakes/brake-parts/types-of-brake-fluid.htm
“Brake Fluids: Glycol and Silicon-Based Explained”
May 14th, 2014
“DOT 3 and DOT 4 Brake Fluid: What’s the Difference?”
John Baker, March 20th, 2019