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OK to Mix Synthetic and Conventional Brake Fluid?

I recently got a used car, and I noticed this past week that clutch fluid is low. I don't know what kind of clutch fluid is in there, only that it is most likely DOT-3 fluid, per the manual recommendation. I bought some synthetic DOT-3 - can I add it worry-free without knowing exactly what's already in there?


  • Yes, as long as both fluids are DOT 3, you can mix without worry. If this is the Miata, the OEM fluid is DOT 3.
  • I agree about fluid type mixing, harmless. Most important for new owner of USED vehicle is Why is it low? A small leak? It is a simple design with master and slave being the only devices.Even if you think it just evaporated it would mean the fluid is very old. Get a helper and add a full pint by bleeding it out the slave cylinder at the transmission.

    If you are handy you can remove the intake brace (behind alternator) and then snake your arm back to the bleeder valve with a 10mm wrench , otherwise you will need to jack it up and come from the bottom.

    Always disconnect battery in trunk before servicing.

    Good luck. I have had my 99 since 98. You won't like your Miata if you loose the clutch from a leak.
  • Aren't all brake fluids 'synthetic'? Not like they come out of a barrel of oil...

  • All brake fluid is synthetic. As long as your can of brake fluid does not say silicone-based, it is likely the only change made to new "synthetic" brake fluid is the label.

  • No guys, not all brake fluid is synthetic
  • Then where's it come from? I don't know of any other way to make a glycol ether, than to 'synthesize' it in a chemical plant.

  • They harvest the glycol crop and squeeze out the brake fluid.
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