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Can you mix Sythenthic DOT3- DOT4 Brake Fluid

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Old 04-14-2009, 11:28 AM   #1
spedaleden
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Default Can you mix Sythenthic DOT3- DOT4 Brake Fluid

I am flushing the brake system. This is a C4 and Master says use DOT3 the fluid I have is Valvoline Synthetic DOT3 DOT4. Can I pour it in with DOT 3 or should I use plain DOT3

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Old 04-14-2009, 12:56 PM   #2
2armor
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I believe they are compatible. The DOT 4 container says 3 / 4 right? The only difference I know of is the DOT 4 has a higher wet and dry boiling point. I've seen resorvoir lids that say dot 3 0r 4 too.

At the least heres a bump-
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Old 04-14-2009, 12:59 PM   #3
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You can not mix synthetic with conventional brake fluid, no matter what the rating. Don't do it.

Hans
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Old 04-14-2009, 01:58 PM   #4
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Quote:
Originally Posted by Wrencher View Post
You can not mix synthetic with conventional brake fluid, no matter what the rating. Don't do it.

Hans
Thanks
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Old 04-14-2009, 02:20 PM   #5
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SILICONE brake fluid cannot be mixed with conventional fluids, but Valvoline Synthetic Dot 3/Dot 4 "Mixes well with conventional fluids".

http://www.valvoline.com/pages/produ...sp?product=138

Its dry/wet boiling points are 480*/311*, btw.


TSW
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Old 04-14-2009, 02:30 PM   #6
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Quote:
Originally Posted by TheSkunkWorks View Post
SILICONE brake fluid cannot be mixed with conventional fluids, but Valvoline Synthetic Dot 3/Dot 4 "Mixes well with conventional fluids".

http://www.valvoline.com/pages/produ...sp?product=138

Its dry/wet boiling points are 480*/311*, btw.


TSW
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Old 04-14-2009, 02:49 PM   #7
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Silicone is DOT 5. His is syn 3/4. This should be compatible.
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Old 04-14-2009, 04:30 PM   #8
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Hi

You can not mix synthetic with conventional brake fluid

Aren't all brake fluids synthetic except for the silicone fluid ?
I don?t know of any mineral brake fluid.

Dot 3 is well mixable with Dot 4 as mentioned B4.

Some believe that C3 systems should not be filled with Dot 4 due to premature brake piston seal failures. Something to do with a different additive or so.

Rgds. GŁnther
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Old 04-14-2009, 06:03 PM   #9
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Quote:
Originally Posted by Wrencher View Post
You can not mix synthetic with conventional brake fluid, no matter what the rating. Don't do it.

Hans
Geez...You need to get your facts straight before making such a grand statement.

The synthetic DOT4 is not silicone, and it can be mixed with DOT3....
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Old 04-14-2009, 09:23 PM   #10
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good grief....I noticed that none of the naysayers said why you can't mix synthetic and standard, they just say you CAN NOT DO IT.
whatever. mix away. won't hurt anything, won't kill seals. that's a bunch of nonsense.

and by the way. I HAVE mixed regular with synthetic and haven't crashed yet!!
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Old 04-14-2009, 11:17 PM   #11
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Keep your seatbelt cinched up tight....
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Old 04-15-2009, 12:33 AM   #12
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Thanks Guys, I used DOT3 just to be safe
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Old 04-15-2009, 01:02 AM   #13
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An interesting article on brake fluids:

http://www.afcoracing.com/tech_pages/fluid.shtml
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Old 04-15-2009, 01:34 PM   #14
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I should have posted in more detail. Yes, silicone is a definite no-no as far as mixing goes and yes you "can" mix the rest, but I highly recommend against it. True, you may never see a problem in a street car, but why take a chance? I flush mine annually to prevent/reduce moisture content, plus I always change it after a day of racing, and I exclusively use Ford DOT 4 fluid. Why? After 35 years of repairing and racing (IMSA, SCCA Can-Am and Trans-Am, club GT-1,2,3,4) I find what works and causes the least problems. I don't mix oil, coolant or gear lube either and it might be overkill, but I don't have problems and I've repaired other's stuff because of it. No offense to the others, but that's how I do it. The great thing about this forum, you get lots of informed opinions and you get to make a more informed decision base on that.

Hans
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