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Brake Fluid ... How many Dots?


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What is the preferred brake fluid to use in a 2002?

Dot 3,4,5 or 5+ ?

I know the Dot 5 is silicone and does not absorb water. Found this out the hard (expensive) way when I put it in my seldom-used BMW R100S motorcycle.

Any moisture collects in big drops and sinks to the lowest point in the brake system (bottom of the calipers and slave cylinder). Creates a big rusty mess!

Dot 3, 4, and 5+ are hydroscopic and hold any water vapor in suspension. They all have slightly different "wet" boiling points, but don't differ significantly.

Dot 3 and 4 have different viscosities, but which is better and why?




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18 minutes ago, BarrettN said:

does anyone know if the blue fluid would discolor the fluid reservoir? 

I swap ATE Super Blue and regular fluid all the time - haven’t ever noticed a color change on the plastic MC reservoir…


IMHO, if your fluid spec is DOT 3, you should run a newer top-quality DOT 4. ( I like Pentosin Super).

Edited by visionaut
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23 minutes ago, BarrettN said:

I've always liked using ATE dot 3 fluid and alternating between using the blue and gold fluid, it makes flushing a snap - just flush until the fluid changes color. I haven't done this on my 02, does anyone know if the blue fluid would discolor the fluid reservoir? 

Hey, yellow and blue make green! 

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I use either Castrol or ate.


What I have noticed is that if say, your clutch system is a bit worn, then Castrol usually swells the seals and fixes the problem whereas the ATE does not.


I do change the fluid every year of street use and after a track day.


If you really want to nerd out, you can get a brake fluid moisture meter to check it. I have one. I used it twice......


BTW ATE blue has not been legal in California for many years..... Because, you know, it's toxic.


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1 hour ago, John76 said:

Why?...It's a blue state.

Something about the blue dye. And, CA isn’t all blue. There are some, very, deep blood red areas. Like, confederate flag on a pole mounted to their truck’s trailer hitch red. Like, I didn’t know if they’d like my German car, or if they don’t like any non American made anything.

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ATE blue was banned in the entire US a decade ago. Not because of toxicity, because it was feared dumb users would mistake it for blue washer fluid and put it in the wrong reservoir...


Yes, ATE blue permanently stains plastic reservoirs.


DOT 3&4 are interchangeable.  Main difference is the higher boiling points of DOT 4.  

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