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Silicone or Synthetic, How to Tell

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theleisure

theleisure

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Hi there,

I have a '66 Sprite that's new enough to me that I've never had to refill the master cylinder. I'm not sure if this particular car has silicone or synthetic brake fluid. Is there a test I can do to see which fluid I need? I'll have to refill soon, it looks a little low.

Thanks
 
Get a syringe. Pull some fluid from the reservoir into the syringe. Now spray the brake fluid all over your fender. If your paint peels off, it's conventional fluid. :devilgrin:

If you don't like that idea, supposedly silicon fluid won't mix with conventional fluid. If you have some conventional fluid lying around the garage you might put it in a glass jar then add some fluid from your reservoir and observe the results. This suggestion is purely theoretical as I have not personally tried it.
 
Silicone brake fluid is dyed purple. After a while the dye fades and you're left with a pretty clear, pale fluid. If the fluid is amber or brown, it's not silicone.
 
Thanks for your help guys. While I was at lunch I dug up the PO's phone number and gave him a call. It ends up that he used Castrol GT LMA. New problem is that that brake fluid is not available in Key West. If I want to fill the reservoir but don't feel like waiting a week for shipping is there another brand of fluid that mixes well with that Castrol GT LMA?
 
I think that's a DOT 4 so any DOT 4 off the shelf should be fine.
 
I can attest to the fact that silicone will not mix with conventional fluid. Mis them and they will look just like oil and water.

Brian
 
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