Originally Posted by parapaul
How do you use your car, and what other upgrades have you made to the braking system?
For normal road use, there is absolutely no benefit using anything other than bog standard DOT4 from the nearest motor factor.
If you track it, if you've upgraded to braided hoses, if you've got upgraded pads/discs/calipers and you expect to reach the point of brake fade, then
you should think about using DOT5.1 instead.
The main difference is the boiling point of the 2 types - DOT5.1 has a higher boiling point, but for normal road use this is almost completely irrelevant
DOT ratings and boiling point do not go hand in hand.
Motul RBF600 is DOT 4 fluid.
dry boiling point of 312 °C / 593 °F
wet boiling point 216 °C / 420 °F
Motul DOT 5.1 fluid
Dry boiling point 270 °C / 518 °F
Wet boiling point 185 °C / 365 °F
In my experience with tracking road cars, you can overheat old 'cheap' fluids easily.
You can easily get to this point in on the road, mountian passes whilst on holiday come to mind...
I have always found soft pedal (fluid boiled) sets in before I feel 'hard pedal but no brakes' - characteristic of overheated friction material.
A soft or sinking pedal from overheated fluid normally won't recover and needs bleeding.
New fluids will survive better than 12m old stuff in any case, hence the manufacturers 24m reccommendations.
Anyhow, given the relatively small price premium of something akin to the RBF600 DOT4 (+£10) I would not bother with less in a powerful, heavy car.
Just my 2p.
You can flush quite easily with 1ltr of fluid.
Just empty the reservior to within a few mm of the pickup so you dont pull air unneccesarily.
The top up and bleed each corner. I did mine again recently.