Topic: Brake Fluid mixing???

[Johnie]

K4 - Can I mix DOT 3 with DOT 4 without causing a problem? Or better yet, bleed the brakes down and then add DOT 4 to the master and run that through without causing a problem with anything? I have DOT 3 in there now as that is what the PO said he uses. Was thinking about DOT 4 since it does not collect moisture so readily. I was also thinking about changing over the KO & K1...

[BeSeeingYou]

I have a bottle of what is labeled DOT 3-4 so they are compatible.  I believe DOT 4 is a premium version of DOT 3 with a higher boiling point and absorbs moisture less.  Just don't mix with DOT 5.  I would still drain the old stuff out if you don't know how long it has been in there.

[Bill/BentON Racing]

They 3 & 4 readily mix,if it calls for 3 ok for 4,if it calls for 4 not ok to add 3.It will still mix and work,but not to the specs of Dot 4.Dot 4 has higher wet and dry boiling temps.Bill

[Johnie]

Yah, I flushed the KO, K1 & K4 with new DOT 3 every couple months during the riding season since these are OEM systems that have never been rebuilt. I heard the good on the DOT 4 which is why I was thinking about changing it over. So is the DOT 4 a synthetic or not? If so, will it reek havoc with my OEM seals?

[dusterdude]

dot 4 is not synthetic,only dot 5 is.you can tell whether or not you have dot 5 because 5 is purple in color

[jkot55]

I do not think that you can use DOT4 in these old bikes.  Not sure that the seals will like it.  I would not mix them either.  I have heard many suggest that it is o.k. and to be honest I have no personal experience with mixing.  It just seems that there is really nothing significant to gain from mixing or converting to something other then what it calls for.

[HondanutRider]

From the Honda Common Service Manual (published in 1988):

[Johnie]

From the Honda Common Service Manual (published in 1988):

Excellent info in the service bulletin there.
Thanks...