What are the performance characteristics of brake fluid?
4 Answers
The performance of brake fluid lies in its ability to ensure vehicle braking safety and provide excellent corrosion resistance. Introduction to brake fluid: Brake fluid is a high-concentration liquid with strong water absorption capacity. After being used for a period of time, its water content gradually increases. Brake fluid should be replaced every 2 years or every 40,000 kilometers driven. Alternatively, professional instruments can be used to measure the water content of the brake fluid. If it exceeds 5%, it should be replaced as soon as possible, otherwise it may affect driving safety. Precautions for brake fluid replacement: During the brake fluid replacement process, if air enters the oil pipe, the brakes may feel softer after replacement, potentially causing delayed braking or even brake failure. The complete drainage method can be used to replace brake fluid: open the bleeder valve of the brake caliper, start the engine, and repeatedly press the brake pedal until no oil comes out of the bleeder valve, then tighten it. Add new fluid to the reservoir, repeatedly press the brake pedal until firmness is felt, then loosen the caliper bleeder valve to drain fluid. When the pedal lowers, quickly tighten the valve. Repeat this process twice until no air bubbles emerge from the discharged fluid. Always check the fluid level in the reservoir to ensure it doesn't drop below the minimum mark.
After repairing cars for over a decade, I've found that the most critical property of brake fluid is its high-temperature stability. The heat generated when we hit the brakes can reach several hundred degrees – ordinary liquids would boil and create vapor bubbles immediately, causing a spongy brake pedal. Premium brake fluid acts like a high-temperature warrior, with DOT4-grade fluids having a minimum dry boiling point of 230°C. The most annoying part is its hygroscopic nature – in southern rainy seasons, moisture absorption can exceed 3% in six months, dropping the boiling point by 50°C. That's why it must be replaced every two years. Last time I saw an owner who hadn't changed it for five years – the fluid had turned soy-sauce brown and the calipers rusted through. Remember, it also lubricates pistons and protects metal components from corrosion. If your brake pedal feels soft and squeaks, check your brake fluid immediately.
As a female car owner, I'm most concerned about the corrosiveness of brake fluid. Once during maintenance, I saw a mechanic using brake fluid to clean his phone screen, and I immediately stopped him in shock! This stuff is extremely corrosive—it leaves white spots on car paint instantly and causes rubber parts to swell and crack. The irony is that it must protect the metal components of the braking system. I’ve now learned to check the DOT rating, with DOT 5.1 being the mildest due to its neutral pH. Last winter, my brakes made strange noises, and after inspection, it turned out the brake fluid had absorbed water and frozen, with ice particles scratching the ABS sensor. I recommend avoiding cheap, no-name brands online—my neighbor bought low-cost brake fluid that emulsified within six months, costing over 2,000 yuan to fix the brakes.
Every car modder knows brake fluid flow rate determines pedal feel. During intense track driving, regular brake fluid thickens like syrup under high temps, causing a half-second delay when braking. I've used racing-grade brake fluid that flows instantly even at -40°C. But excessive fluidity increases seal pressure - my modified car requires checking for line leaks every three months. The worst pitfall is mixing different grades causing stratification. Once when blending DOT3 and DOT4, flocculent precipitates formed in the lines, nearly clogging the master cylinder. Performance car enthusiasts should keep a brake fluid moisture tester - replace immediately if water content exceeds 1.5%.
