Brake Fluid Reservoir: Meaning, Location, Functions & More
What is a Brake Fluid Reservoir?
The brake fluid reservoir is a plastic container that stores brake fluid for the hydraulic braking system. It is connected to the brake master cylinder and acts as a reserve supply of brake fluid. The reservoir allows for thermal expansion of the brake fluid as the brakes heat up during use. It also compensates for any small leaks in the brake hydraulic system by providing extra fluid volume.
The main purpose of the brake fluid reservoir is to store an ample supply of brake fluid for the hydraulic braking system to operate safely and efficiently. It ensures a sufficient amount of fluid is available at all times for proper braking function. The reservoir is designed with a cap to prevent contamination from dirt and moisture [1].
Essentially, the brake fluid reservoir contains extra brake fluid that allows the brake master cylinder to keep the brake lines and calipers full. This provides consistent brake pedal feel and reliable braking ability.
[1] https://www.autonationmobileservice.com/i/blog/brake-fluid-reservoir/
Location of the Brake Fluid Reservoir
The brake fluid reservoir is located under the hood of your vehicle, typically near the firewall at the back of the engine compartment. It sits directly in front of where the brake master cylinder is mounted.
On most vehicles, the brake fluid reservoir is a small plastic tank that is transparent so you can easily check the brake fluid level. There will be “MAX” and “MIN” markings on the side of the tank to indicate the proper level range.
The exact location can vary slightly depending on the make and model of vehicle. But in general, glancing at the firewall behind the engine should reveal the transparent plastic brake fluid reservoir.
Consult your owner’s manual if you have difficulty locating the reservoir. The manual should provide the exact location under the hood.
Some vehicles may have separate reservoirs for the front and rear brake systems. So be sure to locate all reservoirs when checking your brake fluid levels.
Functions of the Brake Fluid Reservoir
The brake fluid reservoir serves some important functions in a vehicle’s braking system. According to Pep Boys (https://www.pepboys.com/auto-care/diy/parts-guide/brake-fluid-reservoir), the main functions include:
Stores brake fluid – The reservoir holds the brake fluid that is used throughout the hydraulic brake system. It provides a place to store extra fluid and replenish fluid as needed.
Indicates fluid level – The reservoir has markings on the side that indicate the proper level the brake fluid should be at. This allows easy checking to see that the fluid level is where it should be (https://www.autonationmobileservice.com/i/blog/brake-fluid-reservoir/).
Compensates for volume changes – As brake pads wear down, more space is created in the brake calipers. The reservoir provides extra fluid volume to compensate for this increased space as the brakes wear.
Importance of Checking Brake Fluid Level
Checking the brake fluid level regularly is crucial to ensure the brake system functions properly. Maintaining the correct fluid level helps prevent dangerous situations caused by low brake fluid.
Brake fluid reservoirs are designed to hold enough fluid for safe operation even as brake pads wear down. However, the fluid level can drop over time due to leaks or damage in the brake system. Low brake fluid levels reduce the hydraulic pressure that allows you to slow down and stop. With inadequate pressure, the brakes may feel soft or spongy.
Driving with low brake fluid is extremely hazardous. Braking distances can increase dramatically as the pedal travels farther to apply pressure. In severe cases, it may go straight to the floor with minimal braking effect. Low fluid also allows air bubbles to enter the lines which causes a spongy pedal feel.
Checking brake fluid regularly as part of routine maintenance helps avoid these dangers. Topping it off prevents levels getting too low. This simple procedure takes just minutes but goes a long way in keeping you safe on the road.
How to Check Brake Fluid Level
Checking your brake fluid level regularly is an important part of vehicle maintenance. Here are the steps for inspecting the brake fluid level:
Locate the brake fluid reservoir, which is typically under the hood near the firewall on the driver’s side. Consult your owner’s manual for the exact location. The reservoir will have “Brake Fluid” printed on it and have a plastic cap that can be twisted off.
Check the fluid when the brake system is cold, before driving the vehicle. Brake fluid expands when hot, so checking it cold will provide the most accurate reading. If the fluid level is at the “Full” line when cold, it’s at the proper level.
Inspect the color of the brake fluid through the reservoir. Healthy, fresh brake fluid has a light amber color. If it looks dark, contaminated, or has debris, a brake system flush and fluid change is needed.
If the fluid level is below the “Full” or “Max” line, brake fluid should be added to the reservoir until it reaches the proper level. Use the type of brake fluid recommended by your vehicle manufacturer.
After adding fluid, replace the reservoir cap securely. Check the level again after some use, as the new fluid works its way through the brake system.
What Happens When Brake Fluid is Low?
Low brake fluid levels can lead to some serious issues with your vehicle’s braking system and potentially unsafe driving conditions. Here are some of the major problems that can occur when brake fluid levels get too low:
Decreased braking ability – Brake fluid is responsible for transferring force from your brake pedal to the braking components. With insufficient fluid, you’ll experience a soft, spongy brake pedal and reduced braking power. Your stopping distance will increase, making it difficult to slow down or stop the vehicle.
Brake failure – If brake fluid levels get critically low, you may lose braking ability altogether. The brakes may fail completely, causing a very dangerous situation. Low fluid causes air to get into the brake lines and components, leading to brake failure.
Damage to components – Letting brake fluid run too low allows air into the system. Air compresses while brake fluid doesn’t. The air bubbles can damage brake system components like calipers, wheel cylinders, and ABS modulators. This leads to expensive repairs.
Citation: https://www.firestonecompleteautocare.com/blog/brakes/low-brake-fluid/
Causes of Low Brake Fluid
There are a few main causes that can lead to low brake fluid levels in your vehicle:
One of the most common causes of low brake fluid is a leak in the brake system. Leaks can occur due to worn or damaged brake lines, calipers, wheel cylinders or master cylinder. As brake fluid leaks out, the level in the reservoir drops lower over time. Catching and repairing leaks early is important to maintain proper brake function.
Normal brake pad wear over time is another cause for declining fluid levels. As the brake pads wear down with use, the caliper pistons push out further to keep the pads in contact with the brake rotors. This extends the volume of brake fluid in the system, so the level in the reservoir drops to compensate (Source).
Damage or failure of a brake hydraulic component like a master cylinder, wheel cylinder or brake caliper can also lead to fluid loss and a lowering fluid level. These components contain seals that can wear out or get damaged, allowing brake fluid to leak from the system.
Lastly, brake fluid levels will naturally fall over time with normal brake use. Small amounts of fluid stay on brake parts when released from the hydraulic pressure. Topping off the reservoir every couple years is needed to keep the level in the proper range.
Adding Brake Fluid to the Reservoir
When the brake fluid level in the reservoir is low, you’ll need to add more fluid. It’s important to add the correct type of brake fluid specified for your vehicle. Refer to your owner’s manual to verify the recommended brake fluid type. Common types are DOT 3 and DOT 4 brake fluid. Avoid mixing different types of brake fluid.
Before adding fluid, thoroughly clean the reservoir cap and area around the reservoir opening to prevent contamination. Use a lint-free cloth and brake cleaner. Contaminants can cause brake system damage.
Add fluid slowly and carefully to avoid overfilling. Use a funnel to help guide the fluid into the reservoir. Pour a small amount at a time, checking the level frequently. Stop adding fluid when it reaches the “MAX” line on the reservoir. Overfilling can lead to fluid overflow when the brakes heat up from use.
Be sure to securely close the reservoir cap when finished. Wipe up any spills immediately, as brake fluid can damage paint.
Signs of Brake Fluid Leaks
One of the most obvious signs of a brake fluid leak is finding wet spots on the ground around your tires or under the engine. The brake fluid that leaks out will leave puddles on the ground. According to Tires Plus, you may notice these wet spots near the wheels where the brake fluid drips down from leaking brake lines, calipers or wheel cylinders [1].
Another sign of a leak is low brake fluid level. You may notice the brake fluid reservoir under the hood is low when you check it. A leak causes the fluid level to go down over time as the fluid leaks out. Having a low fluid level can turn on the brake warning light on your dashboard as well [2].
You may also experience symptoms like a soft or spongy brake pedal, indicating issues with hydraulic pressure in the brake system from the fluid loss. Braking performance deteriorates as more fluid leaks out over time. So pay attention if your brakes feel weak or don’t stop the vehicle as effectively [3].
When to Replace Brake Fluid Reservoir
The brake fluid reservoir needs to be replaced if it becomes damaged or develops severe leaks. As brake fluid absorbs moisture over time, most manufacturers recommend flushing and replacing brake fluid as part of routine maintenance every 2 years or 24,000 miles.
According to Mechanics Stack Exchange, brake fluid should be replaced at least every two years regardless of mileage to prevent brake fade. Moisture-contaminated brake fluid can boil at lower temperatures, resulting in vapor instead of hydraulic pressure in the brake lines.
Signs that the brake fluid reservoir needs immediate replacement include external cracks or leaks, low fluid level, and spongy brake pedal feel indicating air in the lines. Replacing old brake fluid regularly helps maintain the hydraulic integrity of the braking system.