What is brake fluid made of?
4 Answers
Brake fluid is a synthetic oil composed of various additives, categorized into three types: DOT3, DOT4, and DOT5.1. Below are some relevant details about brake fluid: 1. Replacement interval: It is recommended to replace the car's brake fluid every two years. 2. Precautions: If the vehicle experiences inconsistent braking performance during normal driving, the brake fluid should be replaced promptly. Before replacement, clean the braking system with alcohol. During seasonal changes, especially in winter, if a decline in braking effectiveness is noticed, it may be due to the brake fluid's grade not being suitable for winter conditions. In such cases, when replacing the brake fluid, opt for a type with lower viscosity at low temperatures.
I deal with cars every day, and brake fluid is mainly made from glycol ether or ester as the base oil, mixed with a bunch of additives. The additives must include antioxidants and rust inhibitors, otherwise the pipelines will corrode over time. This isn't something you can just mix randomly—there's an international DOT standard. The common DOT4, for example, contains borate esters to raise the boiling point. However, it has a critical flaw: strong water absorption. When repairing cars, I often see brake fluid that hasn't been changed in two years with water content exceeding 3%, making the brakes feel spongy when pressed. So, I recommend car owners test the water content every two years—don't wait until the brakes fail to regret it.
Brake fluid is essentially the lifeblood of a car, and I've studied its composition. The base fluid mainly consists of high-boiling-point substances like polyethylene glycol or silicone oil, while anti-pressure additives ensure it remains effective under high temperatures. There are significant differences between types: DOT3 uses glycol-ether bases which are cheaper but absorb moisture easily, whereas DOT5 with silicone oil bases doesn't absorb water but has poor compatibility with ABS systems. The tricky part is its delicate chemical properties – I've seen mixed types turn into curdled tofu-like sludge during repairs. Last time I helped a friend change his fluid, the brake caliper pistons were completely rusted after three years without replacement. So always follow the maintenance manual for scheduled changes.
We ordinary drivers don't really understand these technical details. All we need to know is that brake fluid looks like yellowish watery liquid. The mechanic told me it uses alcohol compounds as base oil with some anti-corrosion additives. The key point is its high temperature resistance, since brake pads can generate over 200 degrees Celsius through friction. What veteran drivers should pay most attention to is moisture absorption, especially during southern rainy seasons. Last time when my brakes felt spongy, testing revealed excessive water content in the fluid. Replacing it immediately restored braking power. Remember not to exceed three years without replacement - safety is far more important than saving money.
