What is the difference between T3 and T4 brake fluid for cars?
2 Answers
The difference between T3 and T4 brake fluid lies in their applicable speed ranges: T3 brake fluid is suitable for speeds between 90 to 140 kilometers per hour, while T4 is designed for speeds ranging from 140 to 180 kilometers per hour. It is crucial not to mix different types of brake fluid due to the following hazards: 1. Mixing can degrade the performance indicators of the brake fluid or trigger chemical reactions, thereby reducing the vehicle's braking effectiveness; 2. The fluid's temperature resistance may decrease, compromising driving safety. The procedure for replacing brake fluid is as follows: 1. Park the vehicle on level ground, turn off the engine, open the hood, and drain the old fluid from the reservoir; 2. Use a funnel to refill the reservoir with new brake fluid; 3. Lift the vehicle using a jack, starting with the rear wheels, and remove the tires; 4. Take off the rubber dust caps on the brake calipers; 5. Loosen the bleeder screws with a wrench, attach a rubber tube to them, and connect the other end to a drainage bottle; 6. Have someone press the brake pedal inside the car while observing the fluid drainage until the fluid level in the engine compartment reservoir reaches the lower limit.
As an automotive technician, I frequently deal with brake fluid issues. The main difference between DOT 3 and DOT 4 lies in their boiling points—DOT 3 has a dry boiling point of approximately 205°C and a wet boiling point of 140°C, while DOT 4's dry boiling point can exceed 230°C, with a wet boiling point around 155°C. This means DOT 4 remains more stable in high-temperature or humid conditions, reducing the risk of vapor lock and brake failure. Another critical aspect is compatibility: DOT 4 is designed for more modern vehicles as it better resists moisture absorption, minimizing system corrosion risks. DOT 3 is cheaper and suits older, simpler cars, but for frequent mountain driving or rainy regions, I'd recommend DOT 4 for enhanced safety. Always check fluid color and moisture content, replace it every two years, and never mix different types to avoid chemical reactions that could damage the system.
