Brake Fluid flush.

[kornholio]

I had a brake fluid flush done. I noticed that on the invoice it says that they used Dot 4 syn fluid. Two questions i have is one is it compatible. The second is did they really use dot syn fluid or did they just put that in the invoice to make themselves look good. I tried to research this and on the internet a lot of people say that 3 and 4 are compatible but to stay away from Dot 5 which is not. Is this correct. All input would be greatly appreciated.

 

[just_phil]

Both DOT 3 and DOT 4 are compatible. Synthetic fluid is not that more expensive. Valvoline synthetic is about the same price as anything else out there, plus you only need 12 oz, that's about $3-$4 worth of fluid. So I'd say it's legit.

 

[kornholio]

Thanks for the reply. I was really wondering if they did use it. Now i know what is in my master cylinder for future, i will continue to use the dot 4 syn fluid.

 

[S197GT]

it sounds like you did not get your brake fluid flushed at a dealership. mazda uses DOT3 brake fluid in the CX-9, which makes sense because DOT4 is generally recommended to be replaced every 2 years. mazda never calls for flushing the brake fluid in their service schedule but does list the brake fluid as DOT3:

"Brake fluid SAE J1703, or FMVSS116 DOT-3" (Page 10-4 in owner's manual)

https://www.amazon.com (commissions earned)

not that DOT4 is bad, it is "better" when it comes to boiling point, but it is overkill, and the issue i would have is that while DOT4 generally has a higher boiling point than DOT3, it absorbs water faster so it needs to be changed more often.

our BMW uses DOT4 and calls for a brake fluid flush every 2 years.

when i do a flush i use a lot more than 12 oz. i usually fill up a 20 oz water bottle and then another half of one with the old stuff; but i probably get some of the new stuff in there, too.

good read:

http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid

"A seldom talked about characteristic is that because of this chemistry, the DOT 4 fluid will have a more stable and higher boiling point during the early portion of its life, but ironically once the fluid does actually begin to absorb water its boiling point will typically fall off more rapidly than a typical DOT 3."

"There are certain DOT 3 fluids with higher boiling points than some DOT 4 fluids. The real differentiating factor is that DOT 4 fluid should be changed more often than a DOT 3 fluid, because of the effects and rates of water absorption."

 

[kornholio]

So I guess that when I am flushing this out again I should go back to DOT 3 fluid then.

 

[S197GT]

i would.

having said that as a practical matter, my wife's bmw is overdue for a brake fluid flush and driving it the other day i couldn't feel anything different. (i think i went about 6 months over last time.) so, i am not saying that you absolutely have to change it in two years exactly. i am sure there are a lot of old used european cars driving around that haven't had their dot4 fluid changed in quite some time.

just something to be aware of.