justin_o_guy2 wrote on 05/15/12 at 18:43:17:I think the Dot this & DOT that is about how much heat the fluid can take w/o boiling. Go with the high number the system can accept,
That is correct.......The rating is based on dry and wet (3.7% water) boiling points. Dot 3 has a dry boiling point of 401 degrees and a wet boiling point of 284. Dot 4 has a dry boiling point of 446 degrees and a wet boiling point of 311. The reason you are supposed to change brake fluid is that it absorbs water from the atmosphere (like ethanol fuel) and the boiling point will be lowered over time - and the fluid can become corrosive once it absorbs enough water.
Dot 5 fluid is silicone based and is used in applications like antique cars and military equipment that may sit idle for a long time. It does not absorb water and will not hurt paint - but it is compressible and will make your brake system a bit more spongy - and it does not meet the higher boiling points.
Dot 5.1 is hard to find but is similar to silicone based fluids and will not hurt paint or absorb water - but is has better compressibility and boiling values. It is used in bicycle hydraulic disc brakes.
If you change from Dot 3 or 4 fluieds to Dot 5 or 5.1 - the system should be drained first then flushed, however there will always be a bit of the Dot 3 or 4 remaining that can cause corrosion. The best thing to do if switching to Dot 5 or 5.1 is take the system completey apart and clean everything.
You probably don't need to worry much about the boiling points for cruising or normal riding. If you are riding on a track or taming the Dragon and using your brakes with little cool down time - then the fluid will be put to the test as the LS650 brakes are small and have little reserve capacity.