What type of fluid is commonly used in clutch master cylinders?

Clutch master cylinders typically utilize brake fluid due to its properties as a hydraulic fluid that can operate within the confines of a clutch system. Brake fluid is specifically engineered to withstand high pressures and temperature fluctuations, which are common in automotive applications. It also has the necessary viscosity to transfer force effectively from the master cylinder to the slave cylinder, allowing for smooth and efficient operation of the clutch.

Furthermore, brake fluid is designed to prevent corrosion and has a high boiling point, which is critical since the clutch system can generate significant heat during operation. This fluid helps ensure that the clutch engages and disengages properly, providing reliable performance in both driving and shifting conditions.

Other fluids mentioned, such as transmission fluid and hydraulic fluid, may be used in specific systems but are not standard for clutch master cylinders. Fuel oil, on the other hand, is entirely unsuitable due to its composition and intended uses.