When should brake fluid be replaced in a hot climate?

My mechanic has advised me to replace the automatic transmission fluid every 15,000 miles in my CR-V due to the extremely hot climate in Phoenix. I do notice an improvement in shifting with regular transmission fluid changes. I am wondering if the brake fluid should also be replaced every time the pads are replaced? Does brake fluid deteriorate like the transmission fluid in extreme heat?

Brake fluid get’s replaced because it’s hygroscopic (absorbs water).

In a drier climate it’s probably not as often as us here in the North East.

50k for me here in NH.

All of my vehicles have their original brake fluid ( 08,06,&…79 )…all of my previous vehicles had only their original brake fluid here in the four corners.

You didn’t say what year your car is, but I’d bet that your manual says to replace it every three years. Does it?

Once it absorbs enough moisture, it becomes less effective in hard braking, plus it can start to corrode parts of the system.

I always replace my brake fluid when I replace the pads, but if you have ABS, then your owners manual may have a brake fluid change on the schedule. Check this first.

Your transmission does not run significantly hotter in Phoenix than it would anywhere else. It is cooled and heated by the cooling lines inside your radiator. It should be changed from time to time, but 30k is usually the recommended interval.

Your mechanic must use the ATF from the Honda dealer, not an aftermarket ATF or a ATF with some additive that is supposed to make it like the Honda ATF. This is very important for your transmission. If anything else was used, you need to take it to a dealer and have a complete fluid exchange done. Do not let a mechanic use a fluid exchange machine that has had anything but the Honda ATF in it.

Every five years is that schedule I’m comfortable with.

For non-ABS systems, I would change the fluid out with each brake job; that would be every 5 years or so.

With ABS every 3 years or so would be best.

Most owner’s manuals don’t call for replacing brake fluid, but it’s a good idea.

My comments are more anecdotal. I used to change the fluid every 2 years when I was in the New England area.The when I moved to CA, I got lax and let the fluid on our Dodge minivan stay there. On the 4th year of ownership, one by one the wheel cylinders and then the master cylinder went out. Might had been coincidence, might had been the car (it was past 100K miles at the time and a lot of other stuff went out too!), or maybe the pedal going to the floor on the first cylinder failure, pushed everything to the extreme. Either was, I learned my lesson and am back to every 2 year fluid changes.

I’ve never heard of a hot climate affecting the life of brake fluid. Brake fluid is specifically designed not to break down when it gets hot, as that’s exactly what happens to it in spades during sustained braking. I’ve always changed out my vehicle’s brake fluid when I have to open up the system for other reasons, like changing the pads or rotors or shoes or wheel cylinders. It isn’t a hot climate here in San Jose, CA where I live now, but I used to live on the border of a sort of high mountain desert area and it would get pretty hot there in the summer. No change to how I treated the brake fluid there vs here. Been working fine so far.

I believe in changing brake fluid periodically, it is in fact hygroscopic (see link) but I’ve never actually seen any comprehensive studies on the issue that establish a recommended periodicity. Anybody got any?

LOL, by the way, spellcheck underlined the word “brake” as misspelled! I know that’s another thread, but I thought it was funny.

15k is to early for tranny fluid change. Most of the guys here do it every 30k. I do it every 50k on my Toyos. As said, se only Honda fluid. I would use the dealer for tranny fluid service.

My brake guys do a brake fluid flush, about every 85k, the life of my brakes or rotors, or every 6 years or so. My experience, no recommendations. First brake work 85k, inner pads worn, new rotors and pads, 85k later pads ok but rotors trashed, took it in due to less brake effectiveness, 85k, do it all i said. Mechanic may have thought it was overkill but I am at like 85k why piecemeal it.

Living in an arid area isn’t going allow the brake fluid to absorb as much moisture as it would if you lived in a rain forest.

So, there has to be a method to measure exactly how much moisture is in the brake fluid.

And there is!


Technically speaking, brake fluid should be flushed every 2 years

By flush, I mean using a pressure bleeder, which puts the system under pressure, and uses the new fluid to force out the old

That said, most owner’s manuals make no mention of a brake fluid replacement interval

To make matters worse . . . for shops and mechanics . . . tv stations and newspapers sometimes carry out “sting” operations on shops and dealerships, looking to see what “unnecessary” work was sold to the customers. Their definition of unnecessary is anything that’s not listed in the maintenance schedule at all, or selling air filters, for example, too soon. Meaning selling them because they are dirty, not because x amount of miles have elapsed.

And brake fluid flushes are high on their list of “unnecessary” work

It’s kind of infuriating, though. Customer comes in for a scheduled service. The air filter is dirty, and the brake fluid is original, and 15 years old. You upsell the air filter and the brake fluid flush. The newspaper calls you dishonest, because the air filter wasn’t due for another 10K and the brake fluid flush isn’t mentioned in the factory scheduled maintenance schedule

What does that mean?

The customer is always right?

The newspaper is always right?


I can see how drier ambient air, like in the southwest USA, can reduce the rate of moisture absorption in brake fluid, but is that the only reason for bleeding brakes?

How many times have you bled brakes only to see dark dirty fluid come out?

Tester: that kit actually measures the amount of copper in the fluid.

From webpage:
Until recently, there wasn’t an accurate process to determine the amount of moisture in the braking system. The Government’s ‘Motor Assurance Programs’ (MAP) established copper as the Industry standard to determine when to replace brake fluid. The Phoenix Systems measures the amount of copper in the brake fluid. The copper level increases when corrosion in the brake
line increases. You ask where does the copper come from? It comes from the steel brake lines. It is an unknown fact that the inner steel brake lines are lined with copper.

does this sound correct?

For the tool junkies among us, there is this brake fluid tester for DOT 3

There is also one available for DOT 4 fluid. I own one of the DOT 4 models, works great.

Back in 1976, I bought a low-mileage 1960 Falcon that had–literally–been driven by a little old lady whom my family knew. Although the paint was chalked, it had racked-up only 18,000 miles in 16 years, and it ran very well…for a Falcon…

That Falcon did get annual oil changes when granny owned it, but the brake fluid had never been flushed. The result is that the fluid was more water than hydraulic fluid when we drained it. That convinced me of the importance of regular brake fluid flushes.

Of course, that car spent its life in NJ, where we do have…a bit…of humidity. If I lived in an arid state, perhaps I would push the intervals outward a bit, but for most locations I think that 3 years/30k miles is a good rule of thumb.

When it comes to brakes, I think that it pays (both literally and figuratively) to err on the side of caution.


“How many times have you bled brakes only to see dark dirty fluid come out?”

If the fluid’s several years old, that’s what you’ll get

Consider this, though . . .

Wouldn’t you rather have fresh, clean brake fluid in your lines, versus that dark dirty fluid you mentioned . . . ?