Question about changing brake fluid

[Spart]

Does not matter at all.

It matters in the cold, as I mentioned above. Higher viscosity fluids impact the operation of the clutch when it's frigid out.

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[Nanook]

It matters in the cold, as I mentioned above. Higher viscosity fluids impact the operation of the clutch when it's frigid out.

I would think that would be an almost imperceptible difference in clutch operation.

 

[Spart]

I would think that would be an almost imperceptible difference in clutch operation.

You'd think wrong, lol. When it's -20°F out, your clutch pedal will not move as fast until engine heat gets into everything, if it can.

It's also one of the very good reasons to delete the CDV, because it exacerbates the problem.

 

[Nothing]

For a street car, look at the wet boiling point. That is the worst condition, get one that is not considerably low. DOT4 will be better, but they are not all the same.

Generally it's said higher performing DOT4 fluids are more hygroscopic and get to the diminished point faster, so if you're not tracking, you will be nearer the lower BP longer. You drive spirited, but if it's street you'd have to be reckless to use the brakes enough to get to any DOT4 boiling point. If you're on a mountain, you will get there quick, just change annually.

The question I have for everybody: where do you dispose your used BF? My only local option appears to be haz mat disposal, which requires a weekday appointment. This is highly inconvenient. Everything else in life from paint, to batteries, to oil is taken at some retail point. Oh and coolant is only haz mat.

 

[Nanook]

The question I have for everybody: where do you dispose your used BF? My only local option appears to be haz mat disposal, which requires a weekday appointment. This is highly inconvenient. Everything else in life from paint, to batteries, to oil is taken at some retail point. Oh and coolant is only haz mat.

Haz disposal for us too. Our local conenience center (dump) will take it. I don’t remember there being a charge, and it’s open nearly every day so it is convenient for us in VA.

 

[zumbooruk]

in addition to higher boiling point (and more hygroscopic) than DOT3, my understanding is that DOT4 lower viscosity is better for anti-lock and traction control systems, since the lower viscosity helps ensure faster fluid movement, enhancing system performance, and DOT5.1 is even more so...

Since I rather not change my brake fluid often and I do not intend to track, I researched and found these DOT4 and DOT5.1 with longer 2-3 year change interval

Castrol React SRF (for comparison since it is popular and have high wet boiling point):
Dry Boiling Point: 320°C (608°F)
Wet Boiling Point: 270°C (518°F)
Change Interval: 18 months

ATE Typ 200 (DOT4)
Dry Boiling Point: 280°C (536°F)
Wet Boiling Point: 198°C (388°F)
Change Interval: 2 years (some sources say up to 3 years)

Bosch ESI6 (DOT5.1)
Dry Boiling Point: 270°C (518°F)
Wet Boiling Point: 185°C (365°F)
Change Interval: 3 years

ATE Super DOT 5.1
Dry Boiling Point: 265°C (509°F)
Wet Boiling Point: 180°C (356°F)
Change Interval: 3 years

interestingly these DOT5.1 have lower wet boiling point than the DOT4 above, which might be a tradeoff for the longer change interval?

 

[Spart]

in addition to higher boiling point (and more hygroscopic) than DOT3, my understanding is that DOT4 lower viscosity is better for anti-lock and traction control systems, since the lower viscosity helps ensure faster fluid movement, enhancing system performance, and DOT5.1 is even more so...

Since I rather not change my brake fluid often and I do not intend to track, I researched and found these DOT4 and DOT5.1 with longer 2-3 year change interval

The ATE and Bosch fluids seem like great options for a daily driven sports car if you keep up with the maintenance.

One thing to keep in mind with brake fluid, as a general rule of thumb:

DOT 5.1 absorbs water faster than DOT 4, which absorbs water faster than DOT 3.

If you truly want the longest service life, performance envelope be damned, use a good DOT 3. Note that corrosion resistance becomes an issue with long service life, which for the majority of folks who never get any serious heat into their brakes, will be the first issue they run into.

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