Synthetic Break Fluid Question

I have a 2008 Buick Enclave, and about two months ago I needed to add some break fluid. I added about 4 ounces DOT 3 synthetic fluid. I found out that if the original fluid was not synthetic, it is not a
good idea to mix them.
The owner's manual specifies only DOT 3 with no mention of synthetic or not (probably because synthetic may not have been around at that time).
The question is, should I have the break fluid changed out (if the original oil is non-synthetic) or is it OK just the way it is?
Thanks,
Dave
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On 3/9/2012 2:01 PM, snipped-for-privacy@comcast.net wrote:

First I'm going to guess you mean brake, not break, right?
And where did you 'find out' it was not a good idea to mix synthetic DOT-3 and regular DOT-3 fluid?
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Oops, yes, brake fluid. I went to NAPA today to get another can, and I then noticed on the shelf below was non-synthetic fluid, DOT 3. I asked the counter guy the difference between the oils. He commented that mixing should be avoided as it can cause clouding. He thought because the car is 5 years old, it probably was not synthetic.
The can I bought earlier (synthetic) says it satisfies all DOT 3 requirement and no cautions statements. I took that as it being OK.
Meanwhile, I have an appointment to be sure I do not have a leak somewhere.
I'd appreciate your thoughts.
Dave
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On 3/9/2012 4:24 PM, snipped-for-privacy@comcast.net wrote:

As long as both cans are marked DOT-3 (or DOT-3/4) there is no problem mixing them. They are compatible. The problem arises when DOT-3/4 is mixed with DOT-5 (silicone) fluid--these are not compatible.
The parts counter guy doesn't know what he's talking about.
All DOT-3/4 brake fluid is glycol based (same stuff as in anti-freeze) and not oil based. That is why DOT-3/4 brake fluid is hygroscopic (absorbs moisture). DOT-5 silicone brake fluid is very different, it is oil based, and won't absorb moisture. But don't ever use DOT-5 in a vehicle that is not designed for it!
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Thanks, Peter for clearing this up for me. Yes, the fluid can, the manual, and the reservoir cover all say DOT 3.
The young counter guy was polite and courteous but innocently had some mis-information.
I have added a total of 4-5 ounces the past months, and as I mentioned, I want to have it checked for possible pinhole leak. Other cars I have owned in the past has normally not needed brake fluid hardly at all.
Again, thanks for getting back to me on this.
Best regards,
Dave
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On 3/9/2012 6:50 PM, snipped-for-privacy@comcast.net wrote:

I'd suggest a careful inspection of the brake system to ensure you don't have an external leak. It is remotely possible the leak won't be visible but that's rare. As you note, it is unusual to have to add fluid, though as brake pads wear the level will drop some as the pistons move out more.
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