While most drivers remember to keep an eye on things like their engine oil and their coolant levels, probably the most overlooked fluid in your car when it comes to scheduled maintenance is your brake fluid. And you don't necessarily need to change your brake fluid as often as you change oil or wiper fluid, but it certainly does need to be maintained and if there's a problem you need to do something about it as soon as you can. When there's a problem with your brake fluid it could potentially inhibit your ability to stop your car on time which could lead to serious damage, accidents, and physical injury. For those reasons you never want to let this one slide for too long.
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Not every driver is aware of actually how to check the brake fluid however since it's not the sort of thing that gets brought up all that often. Checking your engine oil is easy enough because there's a dipstick right there and it's a pretty standard part of routine maintenance. Checking your brake fluid doesn't have to be an intimidating job by any means. If you're interested in any kind of regular car maintenance and taking more control over understanding how your vehicle is working then this is a good thing to know how to do so that you will be less reliant on having to take your car to a mechanic every time an issue pops up. So, let's go over how to keep an eye on your brake fluid, and what you can do about it when something has gone wrong.
What Happens If Your Brake Fluid is Low?
When your brake fluid is low it is going to significantly affect your ability to stop your vehicle when you need to do so. Your brakes are a hydraulic system which means that it’s the pressure of the liquid that allows your brakes to function. As you put your foot on the brake pedal, pressure builds up in your brake lines that forces the fluid to compress the pads against the rotors. That's what stops your wheels from spinning and your car will slow down and stop. When you're lacking brake fluid it's harder to build up that pressure and eventually it will be impossible to do so. With low enough brake fluid, you will simply lose brakes entirely. That's why in movies sometimes people would sabotage a car by cutting the brake lines. No brake lines mean no brakes.
Do You Check Your Brake Fluid Hot or Cold?
As with most fluids in your vehicle you want to check your brake fluid when your engine is cold. This is just a safety precaution to limit any potential injuries that you may experience by playing around under the hood of your vehicle when it's still hot from running. You can get some severe burns if you touch the wrong thing in your engine if it's hot, so make sure it's been sitting idle for a while and it's cool enough for you to be lifting the hood.
How to Check Your Brake Fluid
The process of checking your brake fluid doesn't take a very long time at all. Once you know how to do it you can make it a part of your routine car maintenance that likely only needs to take place every few years. Because brake fluid is part of a closed system it really shouldn't need to be checked all that often and unless there's a problem that requires you to look into your brakes, you don't need to do this anywhere nearly as often as you would check your coolant levels or your engine oil levels.
Step 1: Pop the hood of your car and look for the master cylinder. The master cylinder should be located at the back of the engine bay on your driver side. There will be a small reservoir that's above the cylinder made of translucent white plastic. There will be a cap on top of it. This is your brake fluid reservoir.
Step 2: You should be able to see the fluid level inside the tank through the plastic. The outside should also have lines marked on it indicating the maximum fill and the minimum fill levels. If you have an older car then the reservoir is likely made of metal rather than see-through plastic. If that's the case, then you need to remove the reservoir cap to take a look inside. That could take a little bit of work and may require you to pry the lid off. This shouldn't be an issue unless your car was made in either the early 1980s or before.
Step 3: If your fluid level is showing that it's below the minimum line then you're going to need to add more. This works much the same as any other fluid in your vehicle. You simply pop the cap off the reservoir and pour fluid in as necessary. Remember that brake fluid is a dangerous substance, so you want to avoid spills as much as possible. It's corrosive and can be toxic.
Adding brake fluid also means you need to be sure what kind of brake fluid needs to go into your car. There are actually numerous different kinds of fluids available and if you choose the wrong one that could cause some severe damage. Most cars use either DOT3 or DOT4 brake fluid. However, it's possible your car uses DOT5 as well or even a DOT5.1. You're going to have to refer to your owner's manual to find out for sure what you have in there. If you mix DOT3 with DOT5 that is going to create a gel-like substance which will essentially ruin your brakes and require a full fluid flush to fix. If the kind of brake fluid you need isn't listed on the cap itself, refer to the owner's manual.
Step 4: Once you have topped up your brake fluid above the minimum fill line you can replace the cap. This is also a good time to inspect your brakes. Since your brake fluid exists in a closed system, there are only a handful of reasons why you would have lost fluid in the first place. One is because you've been using your brakes for so long and they've worn down enough to create space in the lines which require you to add more fluid, and the second reason is because of a leak. Both of these would need to be addressed and dealt with sooner rather than later.
Just as an aside, if you're having problems with your brakes but the brake fluid level is full, you're going to want to head to a mechanic to find out what the problem is because something else is going on.
What Causes Low Brake Fluid?
You may be wondering what exactly caused you to run low on brake fluid in the first place if it's a closed system with no reason to run out. The fact is there are a few very common reasons that your brake fluid levels can run low and they are pretty standard for normal brake operations. Eventually this is going to happen, so it's good to know why.
Old Brake Pads: Although it may sound unusual, your brake pads do have an effect on how much brake fluid you have in your vehicle. The way your brakes work, the pressure in your brake lines builds up when you put your foot on the brake pedal. That pressure transfers through the calipers and other parts of your braking system to squeeze the brake pads against the wheel of your car causing it to slow down. Brake pads squeeze, applying friction, which brings the car to a stop. Over time all of this friction causes the brake pads to wear down. That's how they work and it's not anything to worry about. This is supposed to happen. However, that does mean they shrink. When your brake pads shrink it means your brake lines have to push slightly harder to get the brake pads to clamp down because there's more space between them and the rotor. It's only fractions of an inch, but on a long enough timeline it adds up and it creates space in your brake fluid lines that needs to be filled. You have to press harder and the fluid needs to travel just a little bit further to make the brakes work. That space is filled with air which causes your brakes to work more poorly as a result. So while it seems like you're running out of brake fluid what you are in fact doing is creating more space for the brake fluid to fill because the brake pads have worn down. Replacing your brake pads will help fix this problem and topping up your brake fluid is also a good idea as well.
Leaks: A minor leak in your brake line may be insignificant and just cause you to add more fluid to make up the difference but it's still something you'll want to take a look at. Small leaks can turn into larger leaks over time, and that could cause some serious problems if some part of your brake line completely fails while you're driving.
Moisture: Moisture in your brake lines can cause the fluid to break down more quickly and also to work more poorly. The more water in your brake lines the more readily the fluid will boil as a result and that boiling water creates bubbles which force air into the lines and cause the brakes to malfunction. Brake fluid by its nature absorbs moisture from the air, unless you're using a DOT 5 brake fluid which is silicon-based, but very few vehicles run on this. As a result, over time this is going to happen that your brakes will absorb more water which in turn lowers the boiling point and causes air bubbles to form.
How Do You Know If You Need More Brake Fluid?
When the brake fluid is too low then there are some signs that you can be on the lookout for to let you know that you're having a problem.
Warning Light: Not every car is equipped with a brake sensor but most of them are. Low brake fluid levels can cause the brake light to come on your dashboard. This is a safety precaution to let you know that there is a problem that will need to be fixed.
Spongy Brakes: This one is kind of hard to describe if you've never experienced it before, but if you have then it is easy to recognize. You should be familiar with the way your brake pedal responds to your foot, the feeling you get as you push down on the pedal and the resistance that it offers you. As you suffer a problem with low brake fluid you're going to find the brake pedal seems almost mushy like you're putting your foot into mud or a pillow. This could also be caused by too much moisture in your brake lines. That buildup of moisture will end up boiling because your brakes create a lot of heat and that increases the amount of air that's in the lines. Since air can't be compressed the way brake fluid can, it greatly reduces the function of your brakes.
Dirty Brake Fluid: Normally, brake fluid is clear brown however if you do a quick visual inspection and notice that you have dirty fluid, either it's become contaminated and looks thick or even black then that's a sign that you definitely need to change the fluid.
Difficulty Stopping: This one is pretty obvious but if you're having trouble slowing down and stopping when you put your foot on the brakes it's a clear indication that you're having an issue with your brakes. Of course any other problems in the braking system from bad rotors to calipers to brake pads could also cause these problems but the brake fluid can definitely contribute to this issue.
The Bottom Line
You never want to slack off when it comes to keeping an eye on your brakes and how they work. When your brakes go bad, you're putting yourself and every other driver on the road at risk. For that reason, it's good to understand how your brake fluid works, how to check it, and how to replace the fluid when it needs to be done. It's just a simple matter of safety that you never want to overlook