No, you should not mix different types of brake fluid unless they are specifically designed to be compatible with each other. Brake fluids are categorized by their composition and performance characteristics, typically labeled as DOT 3, DOT 4, DOT 5, or DOT 5.1. Each type has different boiling points, moisture absorption rates, and chemical properties.

Key Points:

1. DOT 3, DOT 4, DOT 5, and DOT 5.1: These are the most common types of brake fluid. Mixing DOT 3 with DOT 4, for example, can lead to issues because their chemical compositions are not compatible. The resulting mixture may not perform as expected under high temperatures or during braking.

2. Silicone-Based vs. Glycol-Based: Brake fluids like DOT 5 are silicone-based (non-hygroscopic), while DOT 3, DOT 4, and DOT 5.1 are glycol-based (hygroscopic). Mixing silicone-based DOT 5 with any glycol-based fluid will result in contamination and poor performance.

3. Contamination Risks: If you mix incompatible fluids, it can lead to reduced braking performance, corrosion, or even complete system failure. This is especially dangerous since brake fluid is critical for vehicle safety.

What You Should Do:

- Always check your vehicle's owner’s manual for the recommended brake fluid type.

- Use the same type of brake fluid that is already in your system when topping off or replacing it.

- If you're unsure about the type of brake fluid currently in your system, have it flushed and replaced with the correct type by a professional mechanic.

In summary, mixing brake fluids can compromise your braking system's reliability and safety. It's always best to stick with the same type of brake fluid as specified by the manufacturer.