I can see that my car's brake fluid was changed before by the previous owner but I have no clue if it is dot 3, 4, or 5. I'm planning on swapping out the master cylinder and brake booster next weekend. I know you can mix dot 3 and 4 and not dot 5. But my question is, how can you tell if its dot 4 or dot 5? color? anyway to test it?

 

why not just pick up another bottle for ~$4 and save the headache?

 

I agree. Just flush the entire system.

 

after replacing those parts, just keep bleeding the system until it's a consistent color. Pretty sure after replacing those you'll go through enough fluid you won't have to worry.