Brake Fluid, Dot 4 or Dot 5.1?

[maxibaby01]

Hello guys n gals, bit of advice required please.
Need to replace the brake fluid in my R53 GP.
I honestly can’t recall what was used last time.
Question, is there any benefit to going to Dot 5.1 over Dot 4?
Any brands preferred over others, or are they pretty much the same?
Currently looking at 5.1 from Brembo on Opie Oils, as I’m about to buy 5L of Motul BMW LL-04 oil for the annual oil change.
Any advice comments etc much appreciated. Ta. [emoji4]


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[MINI William]

Dot 5.1 can withstand higher temps so for any spirited driving it will be better off for you.

[maxibaby01]

Yep, thanks for that, didn’t know whether that meant track days only, or general belting around too![emoji4]
Are there and downsides, like working less well at lower temps for instance or becoming more hygroscopic?


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[CiderFex]

I always use Castrol React Performance Dot 4.
Rocky hasn’t had a brake fluid change yet but will get the above when it does.
It exceeds all the temperature requirements of dot 5.1 but is more viscous which means there is a lot smaller chance of it trapping air bubbles.
Dot 5.1 also has silicon in it which just ain’t good for any seals.
I’m sorry the above isn’t more comprehensive but I’m trying to remember all the blurb that I read from well over 6 years ago when I first researched brake fluids.

EDIT:
Just found this better description on Opie Oils website.
“Castrol React Performance Dot 4 Fully Synthetic Car Brake Fluid

Castrol React Performance Dot 4 (Formerly Response Super DOT 4) Synthetic Brake Fluid is a high boiling synthetic brake fluid which far exceeds the requirements of the SAE J1703, FMVSS 116 DOT 3 and 4, ISO 4925 and JIS K2233 specifications. Castrol React Performance Dot 4 (Formerly Response Super DOT 4) Synthetic Brake Fluid is designed for use in all brake systems particularly those which are exposed to extreme conditions. This product has been formulated from mixed polyalkylene glycol ethers and borate ester together with other high performance additives and inhibitors which give ultimate system protection against the effects of corrosion and high temperature vapour lock.

All conventional brake fluids deteriorate during use.

It is strongly recommended that Castrol React Performance Dot 4 (Formerly Response Super DOT 4) Synthetic Brake Fluid should be changed according to the vehicle manufacturers advice. In the absence of such advice, a 2 year change period is recommended.”


Sent from Yorkshire wi a hint o’ sarcasm.

[M600-RKJ]

Just to stop confusion dot 5 fluid is silicon based. Dot 3,4 and 5.1 are glycol based. Dot 5.1 is aimed more at track day applications or very hard road use. Dot 4 would be more than capable of the occasional hoon. I currently run 5.1 because I had a few bottles sitting around. But I never experienced any boiling while running dot 4. So it won't affect anything.

[Craig]

Just to stop confusion dot 5 fluid is silicon based. Dot 3,4 and 5.1 are glycol based. Dot 5.1 is aimed more at track day applications or very hard road use. Dot 4 would be more than capable of the occasional hoon. I currently run 5.1 because I had a few bottles sitting around. But I never experienced any boiling while running dot 4. So it won't affect anything.

What’s also important in that statement is if your going to 5.1 from the lower numbers, then a full flush of the braking system is advised due to the different fluid types [emoji106]

I boiled dot 4 on a track night with the Conv so it got 5.1 thereafter including new pads and was significantly better [emoji2]


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[maxibaby01]

Thanks for all your comments! Will mull over and try to find out what was actually used last time they fluid was changed.

I know that it was Tar-Ox fluid, as they supplied it foc along with S/S braised lines when I bought their discs and pads!

You’d have thought that the 5/5.1 could have been numerated differently to avoid people using them incorrectly by mistake!


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