Brake fluid question

[rpgk]

Hello all.
Just wondering if someone could advise regarding the best brake fluid that should be used. I am hearing differing advice between Glycol (normal) brake fluid and silicon brake fluid. I had been led to believe that Silicon based fluids had a higher boiling point, as such were better - I am now being advised otherwise.
Many thanks for any input offered.

[Stuart H]

It would depend on what your running and hard you brake.

[andrewc]

To acheive a DoT rating, a fluid must exceed boiling points for dry and 'wet' where it gets contaminated with moisture, and DoT 3 is surpassed by DoT 4 and both by DoT 5.1.

Some DoT 4 fluids will have a clean boiling point thats in excess of DoT 5.1's requirements but doesn't get a 5.1 rating as its contaminated boiling point doesn't pass the 5.1 rating.

Racing fluids often have a much higher dry boiling point than road fluids but have poor wet boiling points so would struggle to get a DoT 3 rating for the road. However as brake fluid often gets changed regularly via bleeding this isn't so much of an issue.

Silicone does have a higher boiling point than DoT 4, but less than DoT 5.1, but also is more compressible than the other types of fluid and often results in a spongy pedal - fine for a classic car but not for a race car.

I think the best value for money road fluid for performance is Castrol's Super Response DoT 4 (or whatever they call it now, it changed name recently).

Otherwise AP's range of racing fluids is worth checking out.

DOT 3 - 205°C (dry) / 140°C (wet)
DOT 4 - 230 / 155
DOT 5 - 260 / 185 <- 'aka Silicone'
DOT 5.1 - 260 / 185

[rpgk]

Thank you very much - certainly a better understanding now.

[Al Weyman]

I have never looked back since switching to Castrol SRF before then I used to suffer from brake fade at the end of a long straight in my heavy Camaro race car. I tried all the usual 'race' fluids and none worked but the SRF and I wont ever use anything else.

[robhollyman]

as above, SRF, its not cheap but its by far the best

[MGDavid]

[Al Weyman]

Don't need changing every five minutes either so can work out reasonably economical especially if your brakes faded like mine did, once I had to take to the escape road at the end of the Revitt straight where my cars hit over 140mph due to terminal brake fade, a brown trouser moment for sure! there used to be a race shop in Hendon and I happened to ask the guy in there years ago and he put me on to SRF and it cured it immediately.