Brake fluid recommendations? Dot 3 VS dot 5

GHOST RUSTERS said

I might have misunderstood but I’ve read there’s some consideration between the two with moisture in mind… water displacement I’m assuming? I do live in the Midwest and it’s mighty cold, I certainly don’t PLAN to for the car to be out and about at negative temps, but it will spend its downtime during the winter in an insulated garage… would that be a concern with moisture in mind between dot 3 and dot 5?

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One absorbs moisture (DOT 3), the other does not (DOT 5). So, what does that mean? It means that with DOT 5, the moisture will not mix with the fluid. So the moisture will be "wherever it is" in the system and OUTSIDE of the DOT 5 brake fluid. So, rust and corrosion "CAN" be an issue. I know, we're now gonna get all the "I've been runnin DOT 5 147 years and never had problems" crowd, but that's the FACT and there's no gettin around it.

Conversly, DOT 3 will absorb moisture, since it is water soluble. That means that the fluid will become more diluted over time. How much time? Crapped if I know. A LONG time I guess, since I've seen 50 plus year old cars with the same brake fluid and same brake system and the brakes still worked.

I'm not advocating for one or the other. I'm just stating facts. The DOT 5 is REAL nice if you have a really nice paint job and don't want it to be possibly damaged.


In the end, BOTH fluids should be flushed and changed with new over a period of time, just like all service manuals say. So if done correctly, that would get any moisture out of the system anyway, theoretically.