Brake fluid

[Dudley]

What are the negatives in mixing DOT 3 with DOT 4 in the reservoir...about 2 table spoons full.

[Big Arm]

In my opinion.......I don't think that much would matter. I'd more than likely done the same thing in a pinch.

[M109Dreamer]

The main difference is the temp range that Dot 4 has over Dot 3.

I have always used the Valvoline Dot 3 & 4 in my bikes without issue. You can pick it up at your local auto part store.

Link below shows you what the can looks like.

http://www.valvoline.com/products/br...brake-fluid/28

[Chupaca]

just stay away from the 5...if you prefer you can suck the fluid out and replace it with fresh fluid of all the same kind. Depends on when your due for a fluid change anyway..I always keep the same fluid on hand but if out on the roads I will mix 3 & 4....

[Questions]

The negative affects of adding the DOT3 to the DOT4 system is that it will begin to lower the boiling point of the DOT4 fluid. Just the same, if you add DOT4 to DOT3 fluid it will increase the boiling point. Small amounts will have minor affects on the overall system, but it will affect it. Being that the fluids boiling point lowers due to the fluid being hygroscopic, and absorbing water, if the fluid is not changed at the recommended intervals (2yrs) and on top of that DOT3 is being introduced into the system, the fluids boiling point will not take long to become more like that of an actual DOT3, which can lead to some boiling of the fluid leading to braking issues.

[stillriding]

This thread got me to thinking about a question I've had for a long time regarding brake fluid. We're supposed to use it from a fresh can because the fluid can absorb moisture. But, what if you don't use a whole new can? If you screw the cap on tightly can the fluid be used later? If so, how much later?

[BajaRon]

What are the negatives in mixing DOT 3 with DOT 4 in the reservoir...about 2 table spoons full.

In real life, zero. You'd have to add a fair amount more than this to make any effective difference.