Hey everyone, I have seen what can happen to a system that has both old (dot 4) and new (the dot 5) mixed together. If you want to see what happens...just mix a half a cup of both and let it sit. You'll see the dot 4 seperates to the bottom and the dot 5 to the top (that is if I remember that right)...but does it??? What happens is the dot 4 takes the purple dye out of the dot 5 (the dye only serves the purpose of identifying it as dot 5 brake fluid). The white/milky part of the mixed solution is actually the dot 5. I just thought that you'ld all be interested in what happens to the two being mixed. Now, does it mess the system up?? Can't say that I remember my instructor (from UNOH, Lima, Ohio) saying that it did. I do remember that dot 5 is more expensive, lasts longer, not hygroscopic (absorbs moisture), and has a higher boiling point. Later, chris '70 Imperial LeBaron _________________________________________________________________ MSN Toolbar provides one-click access to Hotmail from any Web page – FREE download! http://toolbar.msn.com/go/onm00200413ave/direct/01/