Brake fluid refresh?

[supton]

Sure, there might be some motion, over long periods of time. Fresh & dry fluid might wick up moisture laden brake fluid, but I can't imagine the process being fast.

I suspect that any quick changing of color is more related to what residue was left behind in the M/C. And mixing with the fluid in the M/C, maybe the first inch or whatever of the brake lines. There is some level of back and forth in this area as you pump the brakes.

 

[50yr Street Mech]

Ok ....You all win. Makes total sense. I get it. I was just tryin to cheat a little bit. Thankfully, I always make sure the bleeders have good caps on them,,,,if not,,,the 8 mm bleeder goes SNAP .... Then you're in a world of doo-doo.....On a RARE occasion, I run into a 10mm bleeder.....

 

[KGMtech]

Did my DOT3 flush for my QX60 this morning. The only problem was my Motive Power Power Bleeder pump system had a cracked hose in the line that goes to the top of master cylinder. Remove hose section, cut out cracked area and re-attach. Do this task about every 2 years, only needs 1 litre of DOT3, so that's usually $20 CAD for the Kleen-Flo brand = good enough.

 

[Mainia]

NO.

 

[Dborch41]

There is some, albeit very slight, circulation of fluid between the wheels and the master cylinder. It's due to a process know as "thermal diffusion", which is the relative motion of fluids arising from a temperature gradient. Basically, the fluid in the calipers gets very hot while it stays considerably cooler up at the master cylinder. Heat seeks cold which does create movement of the fluid even without active circulation.
Early forms of residential steam heat worked on this principle. There was a single pipe from the boiler to the radiator, the hot water would find its way up the pipe where it would cool in the radiator and sink back down, all through a single pipe.
Again, it's not a significant amount of movement, especially from the wheel furthest from the M/C, but it also isn't totally stagnant.

 

[50yr Street Mech]

Some is better than none. Like I said before, If I have the TIME, I'll do a 4 wheel flush. Trying to get things off the list is hard, always another fire somewhere else to mess up you're plans. Never fails. I was doing an easy tune-up on my 2AZ-FE / 4cylinder one day. The next thing I hear is the motor in the HVAC system grinding away like a car metal on metal brakes. Had to stop the tune-up, and address that situation. Always something

 

[willbur]

There is some, albeit very slight, circulation of fluid between the wheels and the master cylinder. It's due to a process know as "thermal diffusion", which is the relative motion of fluids arising from a temperature gradient. Basically, the fluid in the calipers gets very hot while it stays considerably cooler up at the master cylinder. Heat seeks cold which does create movement of the fluid even without active circulation.
Early forms of residential steam heat worked on this principle. There was a single pipe from the boiler to the radiator, the hot water would find its way up the pipe where it would cool in the radiator and sink back down, all through a single pipe.
Again, it's not a significant amount of movement, especially from the wheel furthest from the M/C, but it also isn't totally stagnant.

I think they call it "convection" flow, at least that is what my physics class called it. Its used as emergency backup reactor cooling in subs.

Regarding no circulation in braking system, observational evidence seems to contradict that in my experience. Master cylinder seal wear darkening fluid one week after fluid exchange with a turkey baster suggests very fast wear rates but my MC is 21 yo with 160K on it- It should have worn out 19 yo ago with that reasoning

 

[Carmudgeon]

Rhetorically, what self-respecting mechanic would simply siphon out the contents of a coolant expansion tank and call it a day and job well done?

What self-respecting owner would want a job done in such a fashion for a system that carries greater consequences if a failure occurs?

 

[LordNilesStandish]

Just get a mightyvac or similar. I prefer the ones which pressurise the master.
Then just go around and crack each bleeder until fresh fluid flows. It's an easy job
I know it's a bit more work but changing brake fluid every two years is essential.

 

[Fordiesel69]

Poor mans brake fluid change. Been busy and with this heat here in NC I don't care to be outside much. I hate it when i have to change clothes several times a day because I soak them with sweat. Anyway, is it worth sucking out the brake fluid out of the reservoir and filling back up with fresh every few days to get some fresh fluid in the system until I can bleed each wheel properly? I usually do it when I replace my brake lining but at the rate I'm going that will be years from now since I don't put the miles on like I used to. I wish they wouldn't have banned ATE Super Blue brake fluid. It was nice seeing blue fluid come out an knowing for sure it was fresh at each wheel.

Well......you have to suck out and replenish the resivoir anyways, so yes do that now. Then select a day to bleed each wheel.

I just did my motorcycle, and I had to relearn how to use the clutch and brakes it made THAT MUCH of a difference. 2016 to 2025 was way too long. I will do it ever 3 yrs from now on.