Brake fluid is a critical liquid within your BMW’s Anti-Lock-Brake (ABS) system. As the life-blood of your brake system, it also serves as the hydraulic fluid that your Dynamic Stability Control (DSC) system uses to maintain control of your BMW during emergency maneuvers or collision avoidance. Maintaining the qualities of this fluid is a mandatory service according to BMW, and is performed on a calendar basis regardless of usage, every two years. Lets look at the why and how, to learn more about the #1 most deferred service among BMW owners.

Brake fluid key take-aways:

1. Brake systems are hydraulic. Since brake systems operate on hydraulic principle, a specific hydraulic fluid must be specified for the system. The fluid must not change in volume when compressed and must retain its hydraulic qualities at a broad range of temperatures without a change in pedal feel. The brake system also integrates the stability control systems – some more than others according to their design. These operations rely on a known fluid quality to function correctly. Since these fluid qualities change over time the fluid must be replaced periodically to maintain integrity.
2. Not all brake fluid is the same. Due to design variations, brake fluid is categorized into different types, (i.e. Dot3 or Dot4), and rated by boiling temperature and sometime viscosity. Modern BMW systems use mostly Dot4 fluid with low viscosity for proper function of todays fast-acting stability control systems (DSC). High performance fluids with high boiling temperatures are available for performance use. However, they require flushing more frequently to maintain their performance.
3. Brake fluid is hygroscopic. Hygroscopic means to absorb moisture, and this fluid absorbs moisture regardless of how the car is used- even if it sits unused! A brake fluid is recommended to be changed when it becomes “wet.” Water boils at 212 degrees and its qualities as a hydraulic fluid is poor for this application. As moisture builds within the system, the boiling temperature of the fluid drops. Since braking generates heat, the fluid can boil and cause loss of pressure within the hydraulics, presenting a major safety crisis. Additionally, moisture inside the system causes rust and corrosion to its components. As systems have become more and more complex, this can develop very severe problems and costly repairs.
4. What is dry boil, wet boil? Brake fluid will boil at a certain temperature. A “dry” brake fluid is one that has not yet absorbed any moisture, so the boil temperature is simply the temp at which it boils and become less hydraulically effective. A brake fluid is recommended to be replaced when it becomes measurably wet. We measure this via a hygrometer, as shown in the above image. Any fluid with moisture content above 2% is recommended for renewal. Most fluids will specify a “wet boil” temperature for this point. The boiling temperature drops exponentially as the moisture content increases from here.BMW knows that with genuine BMW fluid in a well maintained system will take roughly 2 years to degrade to this point, hence the designated service interval. An “OEM” brake fluid will offer a great compromise between high dry boil temperature and continued function when wetted. High performance fluids are also available. They are advertised by their highest “dry boil” temperatures which can be as high as almost 700 degrees Fahrenheit! However, often these fluids have a low “wet” boil, sometimes lower than the factory fluid which forces the owner to flush the fluid more frequently. Therefore, consult with us to determine the best fluid for your intended use as more is not always better.

Why is brake fluid service important?

Considering what we know now, we see that anti-lock brake and stability control systems rely on a well-kept hydraulic system in order to function as designed. Of all systems in the vehicle, it could be argued that the safety systems must be well maintained at all times, as we never know when they’ll be needed. Emergencies can’t be planned for, only prepared for.

Since we know that brake fluid absorbs moisture over time, we understand how that can lead to a degradation of not only the performance of your ABS and DSC systems, but also cause long term harm to the system components caused by corrosion and moisture damage. This damage is often diagnosed as seized brake calipers, failed pressure sensors, or a failure within the ABS/DSC pump. On modern BMW’s, some of these DSC pump repair parts can cost upwards of $4000. In almost all cases, repair costs will greatly outweigh any perceived “savings” by deferring this scheduled maintenance.

This service is a very procedural task and typically processed during any other basic visit such as an oil change. If you desire to maintain your BMW properly and thoroughly, this service cannot be overlooked.

How brake fluid is serviced:

Brake hydraulic fluid exists within a sealed system. The only point in which the fluid can be added is from the fluid reservoir under the hood (brake master cylinder). From there, fluid can only be expelled from the opposite end of the system, via the brake caliper bleed screws (located at each wheel). There are “down and dirty” methods to flush some of the fluid, all the way up to the correct method approved by the BMW factory with approved equipment. The methods used will obviously dictate quality, but also whether the costs will be low or high. For the sake of simplicity we will discuss the method approved by the factory which is how it’s performed at Mporium.

1. Fresh fluid is supplied to the vehicle’s reservoir from a sealed tank in the fluid bleeder equipment.
2. The bleeder machine pressurizes the fluid which pushes it into the vehicle’s sealed system, sometimes while pulsating to dislodge any air within the hydraulics.
3. One brake caliper at a time, the technician collects the pushed-out fluid from each caliper bleeder.
4. During each corner, the DSC/ABS pump is activated to aerate old fluid and air from it’s internal hydraulic solenoid channels and valves. *this is often overlooked but necessary to rely on the system in emergency*
5. After all four corners are completed, the equipment is disconnected, cleanup takes place, and fluid is topped up in the reservoir. Fault codes are checked and cleared, system tests performed.
6. The service reminder is reset if all compulsory measures are completed.

Some vehicle such as ///M models with their multi-piston brake calipers require extra steps for their additional brake bleeders at each caliper. Some models take longer due to limited access or additional electronic systems. Since these variables exist, this service cannot be a one-size-fits-all cost.

Compulsory measures and add-ons:

BMW designs their service monitors to include “linked” services. For this example, most BMW’s link cabin air filter replacement to this brake fluid service that happens once every two years. As a result, we see most invoices for brake flush include an additional cost for these cabin filters. Similarly, for many BMW’s every third engine oil change is to include an engine air filter. In order to properly maintain your BMW to the full extent of its design, these service monitors must have the compulsory measures completed in order to be reset.

Mporium BMW specialists do it best:

Brake fluid service is a common service among all makes and models, not only BMW’s. Many euro cars however, require closer attention to these systems due to their technologically advanced systems and resultant complexity. Along with these complexities come specialized procedures for renewing 100% of the fluid within your system hydraulics. These procedures have a high degree of potential to perform incorrectly or insufficiently by quick-lube type shops. Unfortunately, even some euro shops who “should know” how to do the job correctly, don’t. In order to speed up the job of this low profit task, they might skip a lesser critical step such as bleeding the ABS/DSC block in order to get your car out quicker. Choose your shop wisely for such an important task.

There are no shortages of facilities willing to offer super low pricing for a brake flush to get you in their shop to upsell other more profitable work. We recommend to keep your BMW servicing all under one roof so that the shop builds familiarity and history with your car and you as a client. Over a lifetime of servicing, we usually find these overall costs lower than jumping from shop to shop in search of the lowest bidder.

We believe that building a rapport with your BMW shop will lead to the most enjoyable and stress free BMW ownership experience. Supporting your favorite shop helps to ensure their long term prosperity and the likelihood that when you need them most, they’ll be ready at a moment’s notice to help.

If your BMW needs high quality repairs that come with a full parts and labor warranty, contact us today to schedule your service appointment. Mporium BMW is North Texas’ Most Exclusive BMW Specialist located in McKinney, Texas.