Dot3/4 vs 5.1 for daily driver

[KrisZ]

That was my main question. So the water does drop out and sit.

Yes, water will collect at the bottom, pretty much like with any oil.

https://mgaguru.com/mgtech/hydraulics/ht115a.htm

 

[Jetronic]

Interesting, I never heard of the acid issue. Im assuming that is bad for ABS module and various seals?

Borate esters to increase the boiling point, but water and esters canlead to acid formation.

That was my main question. So the water does drop out and sit.

DOT5 and DOT5.1 are totally different things

 

[Jetronic]

I was told 5.1 isn’t compatible with older seals. Is this correct? This is too bad because I believe it’s easier on paint than the 3 and 4.

Dot5 is silicone oil, dot5.1 a glycol (mostly).

 

[barryh]

I was told 5.1 isn’t compatible with older seals. Is this correct? This is too bad because I believe it’s easier on paint than the 3 and 4.

As stated earlier in the thread, 5.1 is glycol based the same as Dot 3 and Dot 4 so it will be fine with the seals and it will still damage paint.

The confusion between Dot 5 which is silicone based and 5.1 which is glycol based arises because the Dot numbers are performance specifications rather than chemistry specifications. That said it wasn't very clever to have two distinctly different types of brake fluid with such similar designations. What hasn't helped is the brake fluid manufacturers starting to label their products as synthetic as if that was something new which may lead someone to think 5.1 is silicone based. Truth is they have always been synthetic.

 

[camrydriver111]

Not to hijack the thread, but on a related note, is it fine to just exchange the brake fluid in the reservoir? I know the best is to bleed all the lines, but without a power bleeder that is difficult.

You need to bleed all lines. The fluid inside the caliper and brake hose will be most degraded and may even have some fine debris from rubber.

 

[Lubener]

But what about 5.1? Hoe does it get the moisture out of the system? I am assuming the water is heavier and settle son the bottom?

Brake fluid absorbs moisture in the system. It does not prevent or eliminate moisture from forming in the hydraulic system. Use what is recommended in your owners manual and flush the system at every brake job and you will be fine.

 

[KrisZ]

Brake fluid absorbs moisture in the system. It does not prevent or eliminate moisture from forming in the hydraulic system. Use what is recommended in your owners manual and flush the system at every brake job and you will be fine.

Dot 5 doesn’t absorb moisture.

 

[brandon9715]

Dot 5 doesn’t absorb moisture.

DOT 5 is rare and mostly used in military equipment that sits for years. Very few if any consumer vehicles use DOT 5.

 

[KrisZ]

DOT 5 is rare and mostly used in military equipment that sits for years. Very few if any consumer vehicles use DOT 5.

I get it, but it is still brake fluid, so we cannot make generic statements that brake fluid absorbs water.
And OP, despite confusing the dot numbers, was specifically asking about the dot 5 fluid and how it interacts with water.