The benefits of Dot 5 are that it is not flammable, does not take on moisture so you don't need to flush it. It was developed for the US army for trucks etc that sat in storage for long periods but could still be operational ready without a load of work.
I used it on some classic cars in the UK.
3 things:
1: it's expensive.
2: It's a PITA to bleed. Much harder than normal.
3: It gives a spongey feel to the lever or pedal.
They tried to introduce it in motorsport for fire reasons but the drivers hated the pedal feel.
If you want to use Dot 5 it is better to use it with an all new system. You can empty & flush but you risk the seals swelling up (they will have absorbed some of the Glycol stuff over the years) & causing the brakes to seize.
The higher the number you go with the normal stuff with 5.1 being the highest then the higher the boiling point. They also become increasingly Hydroscopic so take on water much faster.
Having used both types my own opinion is to use Dot 4 (more common in the UK, Dot 3 seems to be most common here) & change it every couple of years.
Using fluid from a sealed container is not always a guarantee of moisture content, I read a report of fluid from several suppliers that was quite highly contaminated in un-opened bottles!
Dan
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