Hi all
So I've had this problem with my 4Runner ever since I've bought it. No matter how much I've changed fluid and bled my brakes, my brake fluid always turns green after a short period of time, and I'm curious if anybody can think of a reason why or if anyone else has the same problem.

My car still stops alright, but whenever I replace the fluid and bleed my brakes the pedal is MUCH firmer - then slowly the pedal gets very soft as the color changes and eventually I need about twice the pedal travel just to bring it to a stop, almost using all the travel everything I got.

Over the past 4 years I've bled all four corners easily over 10 times and have gone through countless bottles of fluid. Every time I bled them I wouldn't stop until the fluid coming out was just as clear as what was going in, but the longest it seemed to stay away was maybe 2 months at absolute best before it all turned just as green. I realize there's probably a good amount trapped in the ABS box doing this, but I don't see a way of how you would/could clean it out. Is it just time for a new one maybe? Even then I very rarely have ABS activate so it shouldn't be circulating, right?

I ask because if you do a google search for causes behind green brake fluid you'll get every possible answer under the sun, everything from "there's algae in the system" to "you gotta sacrifice a goat" - and not a single one of them related to 4Runners, or really any cars from the 90s for that matter.

Pic related is my master cylinder. Green as a Jolly Rancher, except this time it's still pretty clear; typically when I bleed my brakes it comes out looking like swamp water. This fluid has only been ran since mid September, and my ABS has been off the entire time (haven't gotten around to replacing the front left sensor)

Sorry the pics are so huge, I tried to downsize them to 20% but I guess that's just how it goes now.

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There is a way to measure the amount of moisture in your fluid, you might google that. Since you live in Washington, high humidity all the time, I'd get a new cap for the master cylinder and see if that helps.

Just gave her a quick poke with a multimeter and only got 0.09v at the highest, and she liked to settle around 0.08v
I suppose I could spend the $20-40 on an actual tester too but it should still read higher if it was waterlogged, 0.3v is the max of what you wanna see

I have not encountered this...that I've noticed. Brake fluid seems to always slowly turn a dark brown/grey color over a period of months/years .
Does it do this across different types/brands of brake fluid? DOT 3, DOT 4?
Maybe check/have it checked for copper contamination using the paper test strips.
It can't be water contamination over just a couple of months, can it?
If it was me, I'd find a brake professional and ask if it matters that it turns green.

Just how green is the fluid? I feel like the container might make it look a little darker than it is.

I don't think living in a humid climate is causing your green color. I haven't changed my fluid in almost 4 years, all those years I spent in Washington from Aug-May, and spent another summer in the oppressive New Jersey humidity. The pedal is still firm, and my fluid isn't green.

I don't think the brake system contains any copper that could corrode to green. Has the brake system been worked on before?

I would doubt it's humidity related as well, we get a lot of rain yeah but our humidity in general is pretty low - certainly nothing compared to states like Louisiana and I certainly don't see anybody from there having the same issue. For example a very humid day to us is like 50%

The most extensive thing I've done to my brakes aside from renewing rotors/pads/drums is replacing the left-rear brake line sometime last summer, when it twisted and snapped while trying to throw in my locker. I did use some nickel+copper line to repair it, but my issue was persisting long before that so I doubt it's the cause. It's also the same tubing we've had on our Jeep for clear over a decade and it hasn't given that car any grief either. I haven't noticed it change with brake fluid, pretty sure I've grabbed DOT3 every time but I've definitely grabbed different brands of fluid

If test strips can test for contamination like that I'll go and snag some tomorrow for good measure. Probably a couple bucks well spent and would provide some more info

What sucks is I used to work with a brake wizard - literally known around here as "The Brakes Guy" because he completely rebuilds and upgrades braking systems for all sorts of classics and race cars as a side job. Dude knew EVERYTHING. But unfortunately I left the place back in 2021, and never thought about asking him when I was there

If you "Google" problem answers are:
Copper levels high enough it will turn green
Water in brake fluid and copper in brake lines, very common on GM cars

Curious what you find. I just bled mine a couple weeks ago and had the same thing, very clear but very green fluid. It was all flushed out probably 1.5 years ago when replacing the master cylinder and calipers.

Like you mentioned, it was not dark or cloudy at all, just green. Have not necessarily noticed any performance issues


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I use the DOT4 synthetic and the fluid seems to not want to absorb moisture like the other stuff does.


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I too use synthetic, for the less water absorption. I use penzoil and its not quite clear and looks green in the reservoir but not that green

Can you post a picture of the fluid on a white paper towel or piece of paper? Some of the reservoirs I've seen on Toyota's age green for some reason.

Here's a cotton swap dipped inside, it showed up on camera the best (but still not great, it's a little more green in person). I used to have a clear bottle filled with a bunch of it, but apparently it got dumped into the waste oil at some point, that would've been perfect
My reservoir definitely has a tinge to it, I can see the plastic itself is green where the small air pocket is. Whether that's from age or getting dyed by the fluid I'm not sure. Unless the fluid is eating it? Doesn't seem likely but it is almost 30 years old now. The reservoir DOES make it look much more colored than it is though

Had to order test strips online. Nobody around me had them; NAPA offered to order the $80 kit but for some reason couldn't order the $20 kit, and they'd both arrive Thursday regardless if I bought online or in store. Should be here in a couple days, then I'll have a better idea of contamination

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It's preparing early for St. Patrick's day. You could have tried a pool supply store for copper testing strips. Used to do that test all the time when I worked at a pool store.

Don't use DOT4 fluid, it's meant to withstand higher temperatures but it will absorb more moisture from the air than DOT3. DOT3 is what the manual says to use.

Huh, would've never thought of that. Good to know for the future

I’ve been using it for years…..


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