Hi guys. Every car manufacturer has a recommended interval for replacing brake fluid, but you rarely hear of anyone doing it because the system causes such little trouble.
It is correct that brake fluid loves to absorb moisture which is why we always keep containers covered and sealed. Besides leading to corroded metal parts, that moisture leads to one form of brake fade. Brakes can easily get way too hot to touch, and that heat migrates into the brake fluid. Brake fluid boils at well over 400 degrees Fahrenheit. Water boils at around 212 degrees, then it turns to a vapor which can be compressed. That causes a low and mushy brake pedal.
We're taught that this moisture can even be humidity in the air that makes its way through the porous rubber flex hoses. I don't know if I believe that or not, but that would be a time issue, not a mileage issue. Also, don't get excited when your brake fluid turns dark. That's from being hot many times, and is normal.
If you live in the rust belt like I do, it's not uncommon for metal brake lines to rust out and leak. We get plenty of new brake fluid at that time, so periodic maintenance isn't needed for that. For those of you lucky enough to live in states where they don't throw a pound of salt on an ounce of snow, it's easy to replace brake fluid when it's time for new front brake pads. As those pads wear, the pistons move out of the caliper housings to self-adjust. Brake fluid fills in behind those pistons, and that makes the fluid level in the reservoir go down. During other routine services like oil changes when we top off fluids, we never top off or add to the brake fluid. We used to rebuild calipers and wheel cylinders as part of a normal brake job as late as the 1980s, but today those are less prone to causing trouble. Instead, now it is common to just pry the pistons back into the calipers to make room for the new, thicker pads. That pushes the brake fluid back up into the reservoir. Had that brake fluid been topped off previously, now it will overflow and cause a mess.
When you pry the pistons back into the caliper housings, it's a good time to open and clean the bleeder screws, then let the old fluid squirt into a container or drain pan, rather than shove it back up to the reservoir. Do the rest of the brake job, then add new fluid in the reservoir. This is a time when there is something to watch for that can cause trouble. First, don't let the reservoir run empty or the entire system can get air in it that has to be bled out. Add enough new fluid, then we have to stroke the brake pedal a number of times to run the pistons back out of the caliper housings to adjust them. This is where we cause trouble.
By about a year, crud and corrosion builds up in the lower halves of the bores in the master cylinder where the pistons don't normally travel. By pushing the brake pedal all the way to the floor, as some service manuals even say, the rubber lip seals get run over that crud and they can be torn. That leads to a slowly sinking brake pedal, and that commonly takes two or three days to show up. The fix for that is a rebuilt master cylinder.
To avoid that damage, never push the brake pedal more than halfway to the floor
Once you have the calipers adjusted with new, full-thickness pads, the reservoir should be filled to the "Max" line. A 2019 model is likely to have anti-lock brakes. Air that goes down the lines can pool in two chambers in the hydraulic controller and cause a mushy brake pedal. On a lot of systems, that air can only be removed by using a scanner to command the ABS Computer to open two valves during a special "bleed" sequence. Most competent do-it-yourselfers don't have a scanner, so it's smarter to just prevent any air from going down the lines. Even if it does become necessary to replace the master cylinder, I have an easy trick that eliminates the need to bleed at the wheels, as most people think you have to do.
For a vehicle as new as yours, you might consider doing what I did. I have a 33-year-old Dodge Dynasty with less than 5,000 miles, so it hasn't needed any brake work, but I did want to replace the brake fluid a couple of years ago. I used the somewhat time-consuming "gravity-bleeding" method. The car has anti-lock brakes with a really large reservoir. I started by opening a rear bleeder screw and let the fluid run into an old, empty brake fluid container. You can't do this with the large quart-size bottles. Once that little bottle was full of old fluid, I added the same amount of new fluid from the same size container. That way I knew the level was correct without having to be careful in that regard. This got all the fluid in the reservoir replaced. I didn't bother with the other three wheels as that old fluid will be diluted eventually with the new fluid.
For one last warning, if you want to do this yourself, it's faster to use something like a turkey baster to suck the old fluid out of the reservoir first, rather than run it through to the wheels. For every tool you use, be extremely careful to never allow even the slightest hint of a petroleum product to contaminate the brake fluid or parts that fluid can touch. That includes engine oil, transmission fluid, axle grease, power steering fluid, and penetrating oil. Those products will cause rubber brake parts to swell, usually causing dragging and overheating brakes as the first symptom. Repairs for that are extremely expensive as all those rubber parts must be replaced at the same time, and the steel lines must be flushed and dried. I can go into a lot more detail if that becomes necessary, but it's far better to just be careful
Let us know if you have more questions or need some of our wondrous advice.
Saturday, November 15th, 2025 AT 5:41 PM
