How much brake fluid is needed

[moonigan]

I'm looking at changing the brake fluid for something with a higher boiling point. MOTUL RBF600 seems to come highly recommended for track work but I'm unsure of how much I'll need. I've had a read through the owners manual but cant find any reference to indicate how much to buy.

Cheers
Paul

 

[Tweed]

on a non-///M you'll need about 1.5 - 2 litres to make sure the old stuff's gone. Just did my 3.0 with ATE superblue, nice and easy to see when the new stuff's coming through

Perhaps someone will come along to confirm whether the ///M's are the same...

 

[BMWZ4MC]

I've just bought two litres of ATE superblue (and yellow stuff pads all round) for my ///M, so I'll let you know if it's enough after the weekend!

 

[moonigan]

I've just been to a mates garage to arrange to get the fluid changed and he asked me why I was doing it. I explained I wanted something with a hight boiling point for track work and showed him the specifications of RBF600. He then proceeded to dig out a nifty little device that determines the boiling point of brake fluid and tested it on the stuff that is currently in my car (its whatever fluid BMW use when they do a change). The results were enlightening.

The boiling point of the fluid in my car is 272C which exceeds the specification of DOT 5.1 fluid (260C) and is 40C shy of the tested results of RBF600 (312C). So the conclusion we both came to is that unless I am going to be driving the car very very hard on track then there is no need to change the fluid and that doing so would be a waste of cash.

So this begs the question do cars used for track days really need brake fluid devised for motorsport when the stock fluid would appear to be more than up to the job.

Cheers
Paul

 

[Rags]

I've just been to a mates garage to arrange to get the fluid changed and he asked me why I was doing it. I explained I wanted something with a hight boiling point for track work and showed him the specifications of RBF600. He then proceeded to dig out a nifty little device that determines the boiling point of brake fluid and tested it on the stuff that is currently in my car (its whatever fluid BMW use when they do a change). The results were enlightening.

The boiling point of the fluid in my car is 272C which exceeds the specification of DOT 5.1 fluid (260C) and is 40C shy of the tested results of RBF600 (312C). So the conclusion we both came to is that unless I am going to be driving the car very very hard on track then there is no need to change the fluid and that doing so would be a waste of cash.

So this begs the question do cars used for track days really need brake fluid devised for motorsport when the stock fluid would appear to be more than up to the job.

Cheers
Paul

Sales Talk that we have all fallen for?

 

[peddy]

What do BMW use?

 

[mmm-five]

The DOT spec is the MINIMUM the fluid has to abide by - there's nothing stopping someone selling a DOT3 fluid that's more than capable of performing better than DOT5.1 fluid. They might simply not want to bother with the recertification if they've made the same product for years.

DOT3/4/5.1 will be fine more most uses, but that extra guaranteed 40ºC might be the difference between slowing enough for a corner from 130mph or not

Dry Boiling Point
DOT 3......205°C (401°F)
DOT 4......230°C (446°F)
DOT 5.1...270°C (518°F)

Wet Boiling Point
DOT 3......140°C (284°F)
DOT 4......155°C (311°F)
DOT 5.1...191°C ( 376°F)

 

[peddy]

I think the benefits of 5 or 5.1 is evident within time were the brake fluid mixes with moisture. i would think a difference of between 155 and 191 degrees would really show?

 

[BMWZ4MC]

...and the answer is:

A litre is sufficient