7.2.5 Used brake fluids
The brake fluid is subject to very strict requirements, because it is operated in very aggressive conditions: under the influence of high and low temperatures. Therefore, the main indicator, which characterizes the brake fluid is its boiling point: the higher it is, the better. In general, boiling for brake fluid is a way to reduce the braking efficiency to almost zero: once the fluid boils, air bubbles appear, the pedal fail, and braking doesn’t start. Also do not forget that low temperatures can cause the brake fluid to freeze, which will also result in a loss of braking efficiency.
Note
The brake fluid is very hygroscopic. This means that it has the ability to absorb moisture, which is contained in the air. The ingress of moisture into the brake fluid will lead to a decrease in its boiling point and the appearance of ice crystals during freezing, which will instantly reduce the efficiency of the brake system as a whole.
Operating manual is supplied along with the car. In case if it is not inside the car, this manual can be purchased separately. This manual will specify the type of brake fluid, which is classified by the US Department of Transportation - DOT. Currently, the most common brake fluids are DOT3, DOT4, DOT4 + and DOT5.1. Moreover, top-class fluid may be added to the master brake cylinder expansion tank (for example, DOT4 may be added to the tank with DOT3 fluid), of course, provided that both fluids are produced by the same manufacturer. Conversely, do not add DOT3 liquid to the DOT4 tank.
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