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DOT 4 in a DOT 3 system

Discussion in 'Technical and Troubleshooting Torque' started by jd, Feb 2, 2011.

  1. Okay, not specifically bike related but figure it may still be relevant to some older model bikes. I'm planning on doing a major upgrade on my cars brakes very soon (better rotors, better pads, braided lines), and obviously as part of this will also be changing the fluid.

    The cap on the reservoir however states DOT 3 only, but I'm not sure if this is purely because of the age of my car (it's a 1989 build), or if there's a genuine risk of damaging something by using DOT 4 or Super DOT 4. I would like to move up to a higher temp fluid but everything I've looked at so far that states "for DOT 3 or DOT 4" always has in fine print on the back something along the lines of "not suitable for all DOT 3 systems.

    So just wondering why there would be a problem with using DOT 4? And does anyone know of any DOT 4 fluids that would be safe to use?

  2. Smee, I'm well aware of the differences between DOT 3 and DOT 4, that's why I want to switch to DOT 4.

    My question was far more specific. I want to know what problems DOT 4 can presumably cause in a DOT 3 system for manufacturers of brake fluid to be putting a "not suitable for all DOT 3 systems" disclaimer on their bottles. I also want to know if there is a brake fluid manufacturer that guarantees their DOT 4 (or better yet Super DOT 4) is safe for DOT 3. That answer is not in either of the links you provided, and from what I could find with SEARCH has not been asked before.
  3. FWIW, you may find a Dot 5.1 fluid (I think Motul does one) that is supposed to be compatible for all Dot 3 and Dot 4 systems (US legislation FMVSS 611).
  4. Ah ha, think I found the answer to my own question. Just in case anyone else is interested:
    http://www.penriteoil.com.au/tech_pdfs/87_DOT 3 and DOT 4.pdf

    So looks like Penrite 525 Super DOT 4 is the way to go :). The Motul would probably work too, but it's specs. are no better (which is strange for what's supposed to be a 5.1) and I'm guessing like most Motul products it's probably twice the price of anything else.