Brake Fluid Test

Mod Details

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At every service, it’s very important to check the water content of your brake fluid.

The issue is that brake fluid is hydroscopic, meaning that it will pull water from where it can, even out of the air.
The water is distributed throughout the brake fluid which causes a big problem.

Dot 3 brake fluid boils at 205°C
Dot 4 brake fluid boils at 230°C

Water boils at 100°C

Brake calipers get very hot. Much hotter than the boiling point of water. So any water in the system near the callipers will boil. When water boils is releases air. Air can be compressed unlike fluid which severely reduces your braking.

It is possible to lose all of your braking power and your brake pedal just goes to the floor. This is obviously dangerous. So, what you need is a cheap tester unit that tests the water content of brake fluid. I bought mine from Amazon.

Testing is simple. Find the brake fluid tank, remove the lid…

…turn the tester on, select the correct fluid rating (Smart uses Dot 4) and put the end of the tester in the brake fluid.

The tester should give an instant reading. In this case it’s showing 2.7% and a warning symbol. If it shows the warning, you should do a full replace of the brake fluid as soon as possible.

However, over a certain level, the meter has a spaz out, the screen goes red and tells you to stop. If this happens, get your brake fluid changed immediately.