Brake fluid is an integral part of the braking system, but often overlooked unless there is a problem — in which case it could already be too late. Knowing when and how to check brake fluid can keep you safe. Manufacturers vary wildly in their recommendations for how often the fluid should be changed, ranging from every 15,000 miles to those who strive to make brake systems that never need a single flush. Consult your owner’s manual for the proper fluid change intervals (and the properly rated DOT brake fluid to replace it with), and every six months or so, give it a quick visual inspection just to make sure things are as they should be.
Here’s a primer on what you should be looking for:
To check the level and condition of your brake fluid, you’ll need to locate the reservoir under the hood, which on most modern vehicles sits atop the master cylinder, directly behind the firewall on the driver’s side. The majority of reservoirs are clearly marked with min and max fill lines and are translucent so you can see the fluid level without opening the cap.
Generally speaking, your level should not fall below the minimum line unless you have a problem. Most likely, low levels indicate a need for new brake pads and/or shoes. This is not a life-threatening situation, but it’s time to have a skilled mechanic evaluate the condition of your brakes to see if they need replacing. However, a level that has dropped very quickly could indicate a leak in the system and requires immediate attention. Topping off your fluid in either of these circumstances will only be a very temporary solution.
New brake fluid should be clear, and light amber in color. If a quick visual inspection reveals dark, rusty or even inky fluid, it is time for a change. One characteristic of brake fluid is that it attracts and absorbs moisture from its environment over time. When water gets into the brake system, two things can happen.
First, it can rust the metal components in the system, causing early wear as bits flake off into and contaminate the fluid or clog the lines. Second, it lowers the boiling temperature of the brake fluid itself, so that long downhill rides or sudden stops might be too much for your brakes to handle. Many times these problems are apparent upon visual inspection of the fluid, but you can also invest in tools such as chemical test strips to check the amount of copper in the fluid or an optical refractometer to check for moisture.
Fluid is the ideal medium for a braking system because it’s incompressible and therefore able to deliver force directly from your foot to the wheels. However, liquids have their pitfalls, namely, their propensity to boil. If, as mentioned earlier, water has breached the system or too much heat builds up, boiling can actually produce gas bubbles that are compressible and will cause the pedal to become spongy — or worse, to fail altogether. Burned brake fluid needs to be replaced regardless of suggested change intervals.
Knowing how to check brake fluid is a handy and an easy enough skill to master, and knowing when to change it can help keep you safe on the road.
Check out all the chemical products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to check brake fluid, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
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Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter. In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.