# Brake Fluid Question



## bert06040 (Feb 10, 2011)

I have an '05 Passat. Today a buddy and I changed all the rotors and pads on it. He emptied out what he could from the reservior with a turkey baster. When he refilled it, he inadvertently poured DOT 3 into the reservior. I immediately pointed out that the res. stated only DOT 4. He then syphoned it out with the baster and refilled it with the appropriate fluid type, DOT 4. My question/concern is will this cause any damage to the break system? And should I flush the system completely? Or will it be ok as is? Thanks.


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## FCP Euro (Sep 4, 2008)

Has the fluid been pumped through the system before you removed the DOT 3 and replaced with the DOT 4??? If it wasn't pumped through the system, you should be fine if you caught your mistake and refille with DOT 4.


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## bert06040 (Feb 10, 2011)

Well, we hadn't pump the the brakes yet. I caught the mistake then we syphoned as much out as possible. We topped it off with Dot 4 then pumped the brakes. My concern is that it mixed with what was already in the res. and it may have "contaminated" it. I know the boiling points for the two are different, but will this slight blend damage my brake system? Should I bleed it just to be safe?:facepalm:


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## FCP Euro (Sep 4, 2008)

I would bleed the brake lines, and completely refill with DOT 4 just to be safe. Noramally catching it before you were to pump the system would be fine. But better to be safe then sorry, and the brake system is not something to be taken lightly, when it comes to your safety and safety of others.


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## bert06040 (Feb 10, 2011)

That's very true. Thanks.


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## FCP Euro (Sep 4, 2008)

Not a problem at all. Glad to help! :thumbup:


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## O_o (Nov 12, 2009)

Like Justin says, it's probably OK, but why take a chance?


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## spitpilot (Feb 14, 2000)

How old was the fluid in the system?....You should flush fluid every other year as VW reccomends...to remove moisture contamination that can corrode ABS valve block, calipers etc..very expensive to leave fluid in there for years! VW OEM fluid is actually DOT4+..slightly higher wet and dry boiling points...mixing DOT 3&4 won't ruin your system...by DOT regs they must be compatible since you can use DOT 4 in a DOT 3 system...by mixing you will lower wet and dry boiling points...and increase the probablility of brake fade during hard usage (say trailer towing or mountain driving), but do no damage to sealse etc. I'd do a brake flush and call it done for the next two years!


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