When bleeding my Hope brakes, is there a reason why I can't bleed the used oil straight out of the caliper and back into the container that stores the new oil?
DOT fluid is hydrophilic (absorbs water).
Brake boiling/fade can be caused by water in the fluid boiling at 100C Vs whatever the much higher boiling point of DOT is.
I have always discarded DOT.
Someone can no doubt offer a more technical explanation but old DOT fluid - bad.
Also dirt etc in the fluid.
There is the possibility that the fluid is contaminated with moisture as DOT 4 & 5 fluid absorbs it, thus lowering the boiling point. Recycle the fluid at your local tip.
I mean it's basically sloppy seconds, why would you want to reuse it?
Brake boiling/fade can be caused by water in the fluid boiling at 100C Vs whatever the much higher boiling point of DOT is.
It works like that with mineral oil, but DOT chemically absorbs water so it doesn't sit seperately. DOT has a 'dry' boiling point and a 'wet' boiling point, but both are much higher than 100°C.
Thanks all