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Reading my M6 manual...

Brake Fluid:
European Model: SAE J1703 or FMVSS116 DOT-3 or DOT-4
Except European Model: SAE J1703 or FMVSS116 DOT-3

The only difference between DOT-3 and DOT-4 is the boiiling point of the fluid , right ?

In the non european model we can also use the DOT-4 ?

Ok I found something that answer my questions ?

"As a trailing note on the DOT ratings, if your car was designed for a particular type of fluid (especially prior to the development of DOT 4 fluids), you should make every attempt to stick with that fluid! For example, if your car was delivered with DOT 3 fluid, the internal components of the system (seals, brake hoses, and fittings for example) were specifically designed and tested for compatibility with DOT 3. Because DOT 4 fluids contain a different chemical composition, the system may not necessarily react in a positive fashion to the borate esters floating around in the mix."

"In other cases, just the difference in viscosity of the two different fluids may cause the seals to wear at different rates. What starts as an annoying squeak might eventually become a torn seal or worse. The examples could go on and on, but the message here is this: it’s fine to upgrade from DOT 3 fluid A to DOT 3 fluid B, but you should think twice (maybe even three times) before switching from DOT 3 fluid A to DOT 4 fluid of any sort."

"That said, when dealing with modern hydraulic braking systems a numerically higher DOT rating is typically considered to be compatible with a lower DOT rating (except for DOT 5, of course). Unfortunately, this same generality just isn’t true for most older hydraulic system materials."

http://www.stoptech.com/tech_info/wp_brakefluid_1a.shtml

A seldom talked about characteristic though is that because of this chemistry, the DOT 4 fluid will have a more stable and higher boiling point during the early portion of its life, but ironically once the fluid does actually begin to absorb water its boiling point will typically fall off more rapidly than a typical DOT 3.


Ok, another question.
I am planning to buy the Motul RBF 600 Brake Fluid.

The Specifications are:
FMVSS 116 DOT 4 / SAE J 1703 / ISO 4925

The DOT-4 is not an specification for non european model, but the SAE J1703 is OK. In this case is a right choise for this model ?
 

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Ah man, I wish I could help. I was just looking for the brake fluid capacity of the 2015 Mazda 6 and it looks like nobody was answering your question. I'm no expert, but I don't necessarily think its worth worrying too much over. Its hydrolic fluid at the end of the day--and while DOT4 has a higher boiling point than DOT3, I've heard the differences are negligible. Good luck!
 

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Viscosity is also different between the fluids, and for reasons explained in the quoted material, DOT-4 ought to be flushed more frequently than DOT-3. DOT-4 is supposed (required, at least after a fashion) to be backward compatible with DOT-3. However, that’s pretty much on the fluid marketer(s) to check and self-enforce. The DOT brake fluid standard could be much more tightly written than it is.

You pays your money and you makes your choice.
 
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