hydraulic clutch

my car has a hydraulic cluch and the fluid level is in the "LOW" mark i know it uses brake fluid but dont know if i should use DOT 3 or DOT 4, and what if i have DOT 3 and i add DOT 4 or if it has DOT 4 and i add DOT 3 will it mess it up or will it work. cuz i dont know which one it has.
(it looks gray)
thanks

I should say on the cap. Usually DOT 3. DOT 4 is more heat resistant. As for mixing ??????????
Someone here will know about that I am sure.

DOT3 and DOT4 are interchangible, but not mixible. IE if you had DOT3 in your system, and wanted to use DOT4, you would need to flush the system. DOT5 in not compatable with ether. if the fuild is low, you ether have a leak in the system or the clutch is worn down and will need replaced soon.

check the owners manual if its not on the cap.

Top it off, it should say on the cap what DOT number it is. Keep an eye on it, and if you have to add to it too frequently, get it checked out.