Changing brake fluid every year or every 30,000 km

Even for the best brake system, without stable brake fluid, the hydraulic stampede will not able to pass it to the brake calipers, and unable to perform braking effect. Brake oil itself must have good liquidity, in order to transfer the pressure quickly. And brake oil selection is the boiling point of the level. The higher boiling point of brake fluid, the grades also increased relatively of number. For example, DOT 3/4/5, dry boiling point of DOT 3 is 205 ℃, wet boiling point is 140 ℃. Dry boiling point of DOT4 is 230 ℃, wet boiling point is 155 ℃. Dry boiling point of DOT5 is 260 ℃, wet boiling point is 180 ℃.

If you find out that the color of brake fluid has become a black sticky look, it shows the brake fluid has seriously degraded. It will affect traffic safety, and immediate replacement is recommended. 

Why there is a difference of dry and wet point in same specification of brake fluid? Because brake fluid is very easy to absorb moisture, the unopened products is suitable for dry boiling point of the brake fluid. It provides high temperature resistance. And once it has been used, the water vapor infiltrates brake fluid, it naturally become wet boiling point which is a lower boiling temperature during normal working condition. Once it exceeds this temperature, brake oil will begin to vaporize, so that will form bubbles in the brake pipe, seriously affecting the transfer of liquid pressure. Then it leads to brake failure, you can see the regular change of brake fluid is very important for car maintenance. 

Once the brake oil contains too much water, it will significantly reduce its boiling point. In the long downhill for a long time pedaling brake, brake oil will easily form bubbles. And that will cause hydraulic brake failure and in severe cases the vehicle will not be able to stop, which is quite dangerous.

Although the DOT 5.1 brake fluid provide high wet and dry boiling point performance, its strong rubber corrosion and water absorption features actually not suitable for general use.  Unless you change brake fluid after every ride like those racers, otherwise it is recommended that you use DOT No. 4. The average replacement should be every 3 to 40,000 km, if less than this mileage, it should change every year to ensure the brake fluid quality.