What is brake fluid?
Brake fluid is a type of hydraulic fluid used in automotive brake and clutch systems. It is used to transfer force into pressure, and is capable of doing this because it, like all other liquids (everything from water and soda, to other types of fluids) it is not able to be compressed.
There are 2 main types of brake fluid in use today, with the first and most common being glycol-ether based; this brake fluid is sold and labeled as either DOT 3, DOT 4, or DOT 5.1 Brake Fluid. The different numbers in the fluid indicate as they go higher the fluids’ ability to resist boiling. Therefore, DOT 5.1 brake fluid will resist boiling in the automotive brake system at much higher temperatures than will DOT 3 brake fluid. You should always use the type of brake fluid that the vehicle recommends for your application.
The other main type of brake fluid is Silicone based, and is labeled and sold as DOT 5 brake fluid. This Brake fluid is NOT interchangeable or mixable with other types of brake fluids. One advantage of silicone based brake fluid is its ability to resist moisture absorption, which is an issue for other brake fluids (more on this later). Despite its superior ability to resist moisture absorption, DOT 5 brake fluid is in limited use in modern day vehicles.
Why is brake fluid important?
Without brake fluid, a driver would not be able to stop their vehicle in the manner they are used to. Brake fluid is directly responsible for carrying the force from the driver pushing on their brake pedal, and transmitting it as pressure to the brakes on the car.
What can go wrong with brake fluid?
Glycol-ether based brake fluids (the most common type) are hygroscopic in nature, meaning they absorb moisture. From general cooking, most people know that water boils at 212 degrees Fahrenheit. Brake fluid has to be able to resist boiling at over 400 degrees Fahrenheit. The humidity in the air over time contaminates brake fluid, and gradually reduces its boiling point as the moisture concentration increases. If the brake fluid boils and changes into a gaseous state, it can then be compressed — this would feel like the driver of a vehicle hitting the brake pedal, but the car does not slow down.
Other than boiling, brake fluid must be contained in order for it to allow the system to operate under pressure. Any type of leak will prevent the brake fluid from getting its job done. Usually small leaks will be noticed by a driver as a change in the feel of the brake pedal; usually drivers describe the pedal as traveling further than it used to, or requiring less effort to depress the brake pedal. If any of those symptoms occur, it’s a good idea to have your brake system inspected.
How do you know when brake fluid requires attention?
During regular service intervals, automotive technicians routinely inspect the brake fluid on vehicles for: condition, level, and leaks. Using modern testing equipment, technicians can measure the moisture content of the brake fluid by taking a sample from the vehicles’ brake fluid reservoir. When the moisture content is at or above 3%, a brake fluid exchange service is generally recommended.
Some manufacturers have also incorporated brake fluid exchange services into the maintenance schedule for their vehicles. These service intervals are generally every 2 or 3 years, regardless of mileage.
Additionally, if a brake fluid leak is discovered during a routine vehicle service, it should be immediately corrected to ensure proper braking performance of the vehicle. A driver may also notice a change in the way the brake pedal feels when a leak is present; any sudden change in the feel of the brake pedal is grounds for inspection by a technician to ensure everything is in working order.
How much does it cost to service, and why?
A routine brake fluid exchange service generally takes around one labor hour for a technician to complete. The only parts usually required during this service are fresh containers of brake fluid which meet your vehicle’s specifications. Depending on the facility performing the work, you could expect to pay between $150 and $250 dollars for this service to be completed.
Our recommendation
If your vehicle has a service interval specified for brake fluid, follow the manufacturer recommendation for service of this fluid. In the event no scheduled service is specified for the brake fluid, it should generally be replaced if the moisture content is at or above 3% — be sure your automotive repair facility checks this during regular service of your vehicle.
Additional Information
How long does service take, and why?
A brake fluid exchange service generally takes an automotive technician about 1 hour to complete. Based on the repair shop’s workload, your vehicle can usually be returned to you in a few hours. It may even be possible for you to wait for the vehicle to be completed in some cases (but we encourage you to take advantage of AutoNation Mobile Service’s amazing service, which eliminates the need for you do wait for anything!).
Is there a way to reduce the cost of service?
Generally, no. This is a very basic maintenance service. Most differences in price are due to the cost structure of the facility performing the work. The best way to save money on this procedure is to comparison shop for the facility that can offer the best price.
What other work might be associated with this?
Anytime hydraulic parts of the brake system are replaced (such as brake calipers, brake hoses, and metal brake lines), the system must be bled of air. Because this process involves extracting some of the old brake fluid from the vehicle, it’s an opportune time to perform a brake fluid exchange. The fluid exchange can be used to clear the air from the system, as well. . Additionally, this service may be part of a routine maintenance service on your vehicle, and combined with other maintenance services, such as oil and filter changes.
Does the type of vehicle matter?
When performing service to the brake fluid on a vehicle, an automotive technician must verify the correct fluid to use for your vehicle. Each vehicle has a different fluid specified for use, and a technician will generally use the fluid specified by your vehicle manufacturer.
It is important to note that some auto repair facilities may install DOT 4 brake fluid as their standard replacement fluid. This is becoming more common in the auto repair industry. If your vehicle calls for DOT 3 brake fluid, and a shop installs DOT 4 brake fluid, this is an acceptable substitute and can even be considered an upgrade. Since there is negligible difference in price between these fluids, you can rest easy knowing your brake system has that much more resistance to boiling brake fluid.
There are some vehicles with advanced braking systems (Mercedes Benz SBC, for example) that have additional service requirements for the brake fluid. For high end braking systems, please be sure to always have a trained technician for that specific system perform the work.