Two Hawk - 1/8/2021 20:44

All of the above has errors!

Yes dot 3, dot 4 and dot 5.1 are compatible, you just end up with the worst characteristics of both when you mix them, the lower initial boiling point of dot 3 and less desirable moisture boiling point curve on dot 4 as it ages and picks up moisture.
Dot 5 is silicon, incompatible with all others, DO NOT MIX DOT 5!
Simple charts here: https://epicbleedsolutions.com/blogs/faq/whats-the-difference-betwee...
There is also a Dot 4 LV low viscosity (or Dot 4+) for some late model traction control/abs systems.