DOT 3 ,4, or 5 brake fluid indentification.

How do I identify the brake fluid in my latest rod that I did not build.
It appears to be a clear slightly yellow in color with no real overwhelming smell in it's under the floor master cylinder.
I have a bottle of DOT 5 on the shelf but it's purple in color.
I know you cant mix them so should I go for the DOT 3 and hope it works?

 

Good question. I'm not sure if the two would mix together or not, but I guess I'd take a couple of ounces of both fluids, pour 'em in a can and see if they mix together, for starters.

 

take some fluid out of the reservoir and put it on a spraycan enamel painted test panel, to see if it bubbles like paint stripper. If it does not affect the paint, it is 5.

 

Do not mix DOT 5 with either DOT 3 or DOT 4.

DOT 3 & 4 are glycol based and can be mixed. If you fluid is yellow in color, you have one of these in your car. DOT 4 has a higher boiling pt than DOT 3.

DOT 5 is silicone based, purple in color and is silicone based. Dont mix it with anything. For many years Harley used DOT 5 in production, but I believe that they are mostly DOT 4 now.

There is also a DOT 5.1 which I believe is glycol based, but I have never worked with it.

 

Are you trying to get your fill level up? IMO, instead of guessing just drain/refill to your standards. It'll save you a lot of headaches.

 

You can mix 5.1 with 3 and 4 , I just did a full brake job and for the first time used 5.1 and so far have the best feeling pedal I had in a long time. Not sure if it's the fluid that helped so much but I'm happy witrh it. If you think you may have 5 in there you would need to completely flush before going to another type of fluid.

 

dot 3 and dot 4 are compatible dot 5 isn't. dot 5 is mainly only used in newer cars cos the other types can destroy the newer style seals. if it were my car i would be draining out the fluid you have in there and filling it with new clean dot 4 fluid (being sure to bleed it all the way through to the wheels) that way you know whats in there and you know you have good brake fluid.

 

^^^what they said...5 does NOT mix with the other two. If you do you will contaminate your entire system!!!