Flushing brake fluid

You probably won't notice much difference moving to 5.1 I'm sure some here are going to tell you it's not recommended for the system I have one of these cars well a generation two with purple silicone in it and it works just fine but that's another story The dot four is actually pretty good so you can just drain and refill for the most part but if you want to flush I guess you certainly can notice that you're reservoir is still for the most part clear it's not turned black etc because that fluid and the seals don't interact like it used to so you should be in pretty good shape internally is the point

 

I'm not a mechanic, but as I understand it, getting any air in the ABS system requires a rather complicated procedure to bleed out.

 

You don't want DOT 5.

It's hard to switch a car to that stuff even when the car has a simple brake system, and the Prius is just about the most sophisticated brake system on public roads.

When you switch from a glycol-base to a silicone base you need to remove every trace of the outgoing fluid. Disassemble everything, blow air through it, thoroughly dry it for days type stuff.

...and that's assuming all the seals in there are still okay with a silicone-base fluid. Some may need to be replaced, and if they're shaped any weirder than an o-ring I don't know where you'd even find the item.

Stick with DOT 3 or 4 glycol based fluid. The anti-boil safety margin you get from converting to DOT 5 is not something you get close to on the street anyway.