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Dot3 or Dot4??????

Discussion in 'Technical and Troubleshooting Torque' started by Browncoat, Oct 13, 2010.

  1. My brake fluid resevoir cap says dot3 or dot4 on it. So my question is which is better? What is the difference?

  2. Use Dot4, i dont even think u can get dot3 brake fluids anymore, but dot5 isnt compatible. Difference is higher boiling point.
  3. Yeah, you can get it still. ISP has dot3 and dot4 right next to each other. Higher boiling point? so is that something that happens alot? boiling.
  4. The higher the boiling point, the more repeated braking it can tolerate... so for track work, you'd go as high as you can.

    I thought dot 3, 4 and 5 were all compatible, but Dot 5.1 wasn't.
  5. Almost, mister Rob. :)

    DOT 5 is the incompatible one (and can't be used at all on ABS-equipped vehicles). DOT 5 is silicone based; 3, 4 and 5.1 are polyethylene glycol based.

    Wikipedia stoof:
  6. I'd have thought your brakes would fade through pads glazing long before the fluid wanted to boil.. but ok.

    Thanks for the responses.
  7. It's one of the two heat-related 'failure modes' of a hydraulic brake system.


    More prevalent on vehicles whose brake fluid hasn't been replaced frequently, as the brake fluid will absorb moisture over time which turns to steam at ~100*C, creating compressable "air bubbles".
  8. Interesting. Thanks again all.
  9. If you put a layer of molybdenum grease on your rotors, your pads will last forever and the fluid won't boil.
  10. Don't go there mole.