Can you use brake fluid in the clutch reservoir?

No. While brake fluid and clutch fluid are both hydraulic fluids, and compatible, they serve different purposes and should be kept separate. Brake fluid is used to transfer hydraulic pressure from the master cylinder to the wheel cylinders, while clutch fluid is used to transfer hydraulic pressure from the master cylinder to the slave cylinder.

The main difference between brake fluid and clutch fluid is their boiling points. Brake fluid has a higher boiling point than clutch fluid, which is necessary because it must withstand the heat generated by braking. Clutch fluid does not need to withstand as much heat, so its boiling point can be lower.

Brake fluid also tends to be more corrosive than clutch fluid, so it is important to use the correct fluid in your vehicle's clutch system to avoid damage.