Oranoco

Having a discussion on another forumn and the subject of brake fluid came up and he was saying that he recomended the use of DOT5.1 as it has a higher boiling point than DOT4. And that DOT4 deteriates by 39% annually.

Now I am aware that brake fluid is hydroscopic (absorbs moisture) but I was always of the feeling that it was better to use DOT4 (replacing every 18months/2 years) for most fast road applications?

Thoughts and opinions people?

Sp3no

iTrader: (1)

I have been having issues with the brake feel on my ST170 for ages, i changed to steel hoses, new disks, pads etc etc trying to get to the bottom of the terrible feel from the pedal. Turned out to be the 5.1 Dot fluid i was using, never considered this as it was meant to be a high performance fluid, back to DOT 4 now and the pedal is once hard again and everything works as it should!!

Paul_Painter

Dot 4 is mineral based and 5.1 is synthetic. They are not compatible. We had some cars accidentally filled with 5.1 and the lines had to be flushed and the master cylinder and calipers replaced as the seals may have been contaminated.

If you require a better fluid than Dot 4 you should use Dot 4+. This has nearly the same properties as Dot 5.1 but is still mineral based.

Cheers

Paul

Gary F

iTrader: (1)

So what's dot 5.1 used for?

Paul_Painter

I've only ever seen it used successfully in race applications.

klumpy

I'm not sure if DOT4 is Mineral based although you can certainly get Mineral based MTB brakes (Shimano).

DOT 4, like DOT 3 and DOT 5.1, is a polyethylene glycol-based fluid (contrasted with DOT 5 which is silicone-based)

Castrol Response DOT 4 is a high performance, synthetic brake fluid.

Ridgey

iTrader: (5)

Most Race brake fluids are DOT4 rated.

tabetha

Usual rumour stuff!!
DOT 5.1 is not and never was designed for high temperature, it was designed and came into being for LOW temperature.
Dot 5.1 is used primarily is cars with ESP in COLD climates where it's much lower viscosity is a major advantage.
Dot 5.1 typically boils around 270C, where as dot 4 ranges from around 230C to over 300C in road/race fluids.
So in short use DOT 4 but a sports/road/race type one.
tabetha

nick-21

Is it not correct to say that in general dot 5.1 has a higher boiling point than dot 4 (i know you have stated there that dot 4 can be up to 300c but i have never come across dot 4 with a higher boiling point than dot 5.1)

I know i have always used dot 5.1 in my DH bike brakes over dot 4 for this very reason, and why the majority of people do.

Anychance you can show me a dot 4 with this high boiling point? Take it the price is high?

klumpy

http://en.wikipedia.org/wiki/DOT_4

"denoting a particular mixture of chemicals imparting specified ranges of boiling point"

Dry boiling point Wet boiling point
DOT 3 205 °C (401 °F) 140 °C (284 °F)
DOT 4 230 °C (446 °F) 155 °C (311 °F)
DOT 5 260 °C (500 °F) 180 °C (356 °F)
DOT 5.1 270 °C (518 °F) 190 °C (374 °F)

nick-21

That is totally general, castrol do a dot 4 which has a boiling point of 280 which is greater than the 270 of the dot 5.1 that wiki state.

rs-tuner

iTrader: (1)

Learn from the master

http://www.fastfordmag.co.uk/files/2...F275.tech_.pdf

ECOS95

I went for SRF.

tabetha

Tarox road race is what I'd use, just research, I don't buy FF, not my thing really.
tabetha