View Full Version : Thread of the Day: Simple method to determine if DOT5

10-22-2012, 5:54 PM
Sorry if this is a repost I did search and didnít get any hits with anything similar, if it is let me know I will kill this thread. First I am not claiming to be an Expert or that this method is the best or even the only way of determining whether youíre Running DOT5.
So you buy a bike and ride it for a while then the time comes to change your brake fluid. You look at your aftermarket master cylinder and there standing proud is the manufactures name, logo, or design, if anything at all, but nowhere does it say what fluid is in it. If itís a Harley aftermarket master cylinder your guess is as good as any. HD switched from DOT5 to DOT4 in 2006. DOT5 in ONLY compatible with DOT5 you cannot mix any other fluid with it without problems. DOT5 is silicone based and DOT3, DOT4, and DOT5.1 are all glycol based. I am not a chemist and I donít know the chemical makeup of each of them itís based on their boiling points, but if youíre interested thatís what the internet is for have at it! For our purpose it doesnít matter just keep in mind DOT5 cannot be mixed with any other brake fluids but DOT5. If you find that youíre not running DOT5 it 's NOT good practice to mix any brake fluids even if they are compatible. Every time I have run across a glycol based fluid I flush the system and just run DOT4 and I have never had any issues. This method will only tell you if you are or are not running DOT5. It will not tell you if it is DOT3, DOT4, or DOT5.1.

Step1: Acquire 2 small test tubes, an eye dropper, a bottle of DOT4 and a bottle of DOT5. If your thinking well know I am going to have a extra bottle of brake fluid I canít use and its going to go to waste, well youíre a CHEAP ASS, but then again you already know this. It will cost less than the medical bills or funeral if you guess wrong.

Step2: Use dropper to take some old fluid out of master cylinder and put it into each of the test tubes.

Step3: Add DOT4 to one and DOT5 to the other and then shave vigorously, like your jerking it to Megan Fox the rougher the better your results!

Step4: Let both tubes sit for at least 5 minutes. One tube will have a clear separation between fluids like oil and water and one will look like one uniform liquid. If the separation occurs in the one you added DOT4 to then it is DOT5. If the separation occurs in the one you added DOT5 to it is one of the other glycol based fluids.

I am sure someone is going to want to argue about mixing this with that but like I said I am no expert and this has worked for me on multiple bikes when I didnít know what fluid to add.

10-24-2012, 1:47 PM
i learned this the hard way,had dot 5 in my bike put on new pads and all had was dot 4 when i took mt front end apart for powder coat the inside of the master cyclinder looked like crap,didnt seem affect the braking but it defiently does not mix!!

10-24-2012, 1:56 PM
I thought the purple color was dot 5

10-24-2012, 3:11 PM
Will this technique work if you replace Megan Fox with Natalie Portman? If so, thank you for the write up.

10-24-2012, 3:54 PM
I thought the purple color was dot 5

DOT 5 is purple when it's new. It turns clearish brown after a little while and virtually the same as the glycol based fluid.

Good write up sgilliesjr

10-24-2012, 4:19 PM
the is a good tip now I'm going to watch transformers