Brake Fluid. Dot 5 or Dot 4. Silicone or not?

[427SCR]

I have had silicone in my DAX for 30 years! It's great but expensive. The biggest issue is that you cannot simply replace standard fluid with silicone, you have to have a brand new system that is totally clean, with all new rubbers. The greatest advantage is spillage. I have actually used silicone brake fluid to clean my gelcoat! It has no corrosive effect.

[aaronjb]

Actually I think I might have used RBF600 last time - I know there was a point where you couldn't get hold of one of them.. or the other.. whichever is easiest and most cost effective is almost certainly going to be more than enough for most of us!

ATE Super Blue (now Typ 200) is also meant to be very good - I can't say personally as the two cans I have are still sat on the shelf(!) but a friend swears by it, IIRC it's in his Gallardo and his S8 right now, and they both stop well

[MartBlak]

Thanks Aaron,
I was getting my phobic and scopic muddled up.

I have been reading more and am going to get Motul RBF660 as per your recommendation.....though on other sites the RBF600 gets well recommended.  "RBF600 has a lower dry boiling point and a slightly higher wet boiling point. It also has marginally better longevity, needing to be flushed at about the same frequency as RBF660, if not at slightly longer intervals."

Martin

[aaronjb]

DOT4 is hygroscopic - absorbs moisture from the air which lowers the boiling point of the fluid and can corrode steel components. Most common fluid type used in all road cars, however.

DOT5 is hydrophobic which means it repels water and doesn't absorb it, can lead to water accumulation (though IMHO that is not a significant risk in a road car system - moisture will be most prevelant at the reservoir, not the calipers). It is silicone based and must not be mixed with any other fluid.

DOT5.1 is not silicone based, it is basically 'super DOT4' with a higher boiling point.

My opinion: Castrol SRF or Motul RBF660; both are DOT4 but significantly better than DOT5.1 specs, have excellent pedal feel and high boiling points. They're all I use in any car I change the fluid in, and I wouldn't touch DOT5 with a long bargepole..

[MartBlak]

I am 100% sure I could have found the answer to this on the old website but am having to start again now I am at the stage of choosing Brake Fluid.
Google gives you many contradictory recommendations depending on the angle the writers are coming from. I had problems of my old brake fluid stripping off the gel coat and eating into the fibreglass so would like to avoid this if possible (OK, don't spill it is the first solution but accidents and leaks happen!).
If I understand correctly DOT5 is hydroscopic so does not absorb water and then condensation might cause problems in the system? (would this be an issue?) DOT4 is not but boils at a lower temperature? (I will hopefully be doing a few track days but mainly road use).
The question of silicone based brake fluids is one I am interested in....apart from the much higher cost! Are they worth it and are there any problems to be aware of?
Many thanks for any advice
Martin