How to Test the Condition of Your Vehicle's Brake Fluid

Video tutorial on how to test the moisture level in your brake fluid. Testing the moisture level in brake fluid will help determine the brake fluids condition and if a fluid replacement is required. Maintenance intervals for brake fluid replacement will vary between manufacturers, but as a general guideline it should be done at 40,000 miles/65,000km or every 3 years or under any major brake system repairs. Use brake fluid which is only listed for your vehicle, while some types maybe interchangeable, it’s best not to mix them to be safe. Testing the brake fluid can be done under 5 minutes with minimal tools.

Tools/Supplies Needed:

electronic brake fluid tester
brake cleaner
clean rag

Step 1:

It’s important to determine your brake fluid’s condition in order to maintain the safety and prevent premature failure of parts, so this electronic tester makes determine your fluid’s condition easy. I do have a tutorial on how to replace a vehicle's brake fluid, so be sure to check that out. Naturally brake fluid will absorb moisture which is present in the air. The system is intended to be sealed, using rubber gaskets and specific fitting, however sometimes these connections can leak, perhaps the reservoir cap wasn’t tight or is leaking, etc. Even have the cap off the reservoir for extended periods of time will cause excessive moisture to be absorbed into the fluid.

Step 2:

For testing I am using an electronic brake fluid tester. A test can be done in under 5 minutes, is a very accurate test, and determines the boiling point by measuring the amount of moisture within the fluid.

Excessive moisture in the system will cause the boiling point to decrease in the fluid. If the boiling point is decreased, under harder or extreme braking the fluid will vaporize and jeopardize your braking ability. This is pedal fade and means that you’ll lose braking performance. Beyond losing braking performance, it can also promote corrosion, especially when the fluid gets older and loses it’s rust inhibiting qualities. DOT 4 will absorb moisture at a slower rate than compared to DOT 3, but will have a higher drop in performance when moisture is present.

Step 3:

Simply locate your brake fluid reservoir, this is normally located on the firewall, they maybe in plain sight or under a cover. Wipe off the surrounding area so we do not introduce any contaminants.

As you can see on the side of the tester we have various modes that can be selected for which type of brake fluid we area using. Different type of brake fluids will absorb moisture different and also have different ranges in boiling points.

Remove the protective cap which will expose two probes that is to be dipped in the fluid. There is also a little led light to help illuminate a dark area. Power up the tester and the light will automatically turn on. Now we can select which type of fluid is in the vehicle. The type of fluid your vehicle uses will be outlined in the owner’s manual or on the reservoir cap. Press the selection button to cycle through the types of fluid from the list. For this truck, it’s DOT 3.

Remove the cap. Dip the probes in the brake fluid and watch the reading. If you remember I release a tutorial on replacing the brake lines on this particular truck so the fluid is quite new and with have a 0% moisture content.

When removing the probe, it’s extremely important to wipe off the probes to prevent cross contamination and ensure the tester will always have an accurate reading. Also be extreme careful with brake fluid as it can damage your vehicle’s paint, so don’t let it drip anywhere.

Step 4:

For another vehicle, this one has been driving for probably over a year, the reservoir cap actually broke due to it’s age so it wasn’t sealing properly.

As you can see it’s in a tighter area and obviously it fails immediately. So the vehicle is unsafe to drive until the fluid is replaced.