Synthetic brake fluid again?

[karls59tr]

Has anyone heard of water pooling in brake lines in a car that has been sitting for a long time because the moisture in the line separates from the synthetic fluid?

 

[TR3driver]

"Synthetic" ? Or DOT 5 silicone ? They are different things.

"Synthetic" brake fluid is just regular DOT 3/4 with a new marketing term pasted on the label. Kind of like "fresh frozen" fish, the term is basically meaningless. Water will never separate from DOT 3/4, but the mixture does turn very corrosive over time. I lost a TR3A once because the long hard line under the car had basically rotted through from the inside. This is an extreme example, but shows the kind of corrosion that DOT 3/4 can cause (the yellow fluffy stuff is the corroded aluminum)


Water pooling in the lines is a common criticism of DOT 5. Not a matter of separating, just that water will totally not mix with DOT 5. So any liquid water that gets into the MC (like if you remove the top in the rain) will stay separate. But, at least in my limited experiments, the water also remains as a bead, surrounded by silicone (much like the way water beads up on a good wax job). In fact, silicone is what they add for the "wax job" in a do-it-yourself car wash. So since the water is not in contact with the metal, it doesn't cause corrosion.

 

[karls59tr]

So if a car with silicone brake fluid had been sitting for an extended period of time with suspended water in it ,would this possibly cause a spongy pedal?

 

[TR3driver]

No, I don't believe so. However, I have heard stories of air coming out of solution much later, so there might be an air bubble somewhere.