Does it matter if brake fluid is synthetic

jkris

New member
This may sound like a stupid question, and it probably is. But I don't want to die a fiery death because my brakes failed. I'm curious if I bought Pennzoil synthetic brake fluid like in Eddies write up, if it would be bad to pour in if there is the Mopar brake fluid still in the master cylinder. Is there a difference? Will it be safe or do I need to redo the brake fluid in the master cylinder. Please advise before I potentially hose my brake system and become Skeletor. Thanks in advance! The Pennzoil stuff does meet Mopars specs according to the owners manual.


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JeepinLife

Caught the Bug
Just buy a bigger fire extinguisher...

you'll be just fine.. however I have heard that mixing synthetic and conventional fluids together can break down the physical properties of the fluid. But in this case you're not really using it for friction protection


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2nd.gunman

Caught the Bug
I don't know about JKs but on some cars particularly Toyota's it will cause all of the seals to swell and leak requiring a total brake rebuild. It's depends on the seal material whether you'll have an issue or not so if others have done it with no issue you should be ok

I stick with what is recommended on the master cylinder cap just to be safe
 

JeepinLife

Caught the Bug
So I looked into this further and asked a pretty reputable resource of mine and was advised to not mix glycol (dot 3,4,5.1) and silicon (dot 5) break fluids. So just double check the labels. All but the dot 5 is actually manufactured as synthetic but some label it so and charge more... go figure


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cozdude

Guy with a Red 2-Door
So I looked into this further and asked a pretty reputable resource of mine and was advised to not mix glycol (dot 3,4,5.1) and silicon (dot 5) break fluids. So just double check the labels. All but the dot 5 is actually manufactured as synthetic but some label it so and charge more... go figure


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This is true. You can mix any dot 3 brand together and you can put some dot 4 with dot 3. 5.1 and 5 should ONLY be added if it's an emergency but will need to be flushed out with a full brake system flush afterwords.
 

TRLJNKY

New member
Ive seen some nasty brake systems after someone mixed synth and regular. As mentioned earlier, all seals were extremely swollen and the vehicles required a complete brake system overhaul. Ive never tried flushing out conventional and running synthetic to see if same results. Im not sure if the rubber seal compounds are different or if its just a chemical reaction. Good luck. It wast on Jeeps Ive seen this but Id imagine end result would be the same.

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