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Thread: Dot3, Dot4, Dot 5.1?

  1. #1
    Half Boost
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    Dot3, Dot4, Dot 5.1?

    Well I put new stainless flex lines on the front of my car and need to flush the old fluid out. I have forgotten the fluid I used last time what are the preferences.

  2. #2
    Some Boost
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    I use Motorcraft Dot 3 for my track car. Even the Porsche guys use it.

  3. #3
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    Porsche guys using Motorcraft must say something! I seem to remember that Dot 4 is silicone and not good for the street (absorbs moisture?) Dot 3 is the standard in all cars what is 5.1 about?

  4. #4
    Moderator Meotchh's Avatar
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    DOT3, DOT4, & DOT 5.1 are all three glycol based, meaning they will "absorb water". Technical term is the fluid is hygroscopic. DOT 5 is silicone based so it is not hydroscopic. If you choose to run DOT 5 in a car that has always run glycol based fluid, you should perform a very through flush to remove the glycol fluid since it does not play nice with silicon based fluid & is very damaging if there is any moisture in the system. The other important difference in each is the boiling point.

    Here's a little more detailed info I reference back to when needed...
    http://www.advancepetro.com/differentbrakefluid.htm
    Quote Originally Posted by brsvo View Post
    Porsche guys using Motorcraft must say something! I seem to remember that Dot 4 is silicone and not good for the street (absorbs moisture?) Dot 3 is the standard in all cars what is 5.1 about?
    Last edited by Meotchh; 05-31-2017 at 07:47 PM. Reason: My spelling sucks & now I fixed it
    There's nothing more to see here, now move along...

  5. #5
    Some Boost
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    Quote Originally Posted by brsvo View Post
    Porsche guys using Motorcraft must say something! I seem to remember that Dot 4 is silicone and not good for the street (absorbs moisture?) Dot 3 is the standard in all cars what is 5.1 about?
    From my previous research, Motorcraft has the highest boiling point of all DOT 3 brake fluids that are not "race" rated.

  6. #6
    Half Boost
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    Thanks for the info I will do a complete flush of my system and run 5.1.

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