Do you need brake-fluid replacement?

Brake fluid is hygroscopic. It pulls water from the atmosphere gradually over time.

The extra water lowers the boiling point of the resulting compound fluid. Boiled brake fluid is a reeaally bad thing-- the phase change to steam spikes the pressure which can unpredictably lock the brakes on one wheel or another. It takes quite a long time and some bad circumstances to have this failure. But it's good to avoid.

Additionally, the compromised fluid can promote (or at least not resist as well) corrosion damage inside those expensive brake booster valve bodies. This is a much more Prius-specific problem.

So read the maintenance manual again. It's in there for mine, and ours is about due.

 

Okay well that trips over one of my long-standing problems with Toyota's maintenance manuals.

They clearly say you should be inspecting that brake fluid's condition every 15,000 miles. But they don't tell you what the pass/fail criteria is.

You're not just going to look at it, judge the "condition" and shrug and walk away, are you? Well, hopefully not.

...but what exactly do they want you to do? They don't say. The implication is that if you don't know enough to judge the condition of brake fluid, you should take it to a pro. But it doesn't even spell that out.

That does not leave you off the hook.

You can buy testers and you can study the topic to your own satisfaction- but you should be aware of the general risk (steam flashover) and the specific risk (the Prius brake booster) and factor that into your interpretation of the maintenance guideline.

 

Well, they should be dipping one of these in there - before telling you need to change it.
Brake Fluid Tester Pen 5 LED Auto Oil Moisture Diagnostic Tool For DOT3 DOT4DOT5 | eBay
I think Honda or VW states 3 year replacement. I don't recall which one, just remember reading it somewhere.

 

I stopped getting hustled and swindled by the dealer. I just perform the brake fluid flush myself with an inexpensive bleeder bought online and with a toyota specific brake reservoir cap. All inexpensive in today's money.

I checked my dash camera after my most recent dealer visit. They train their tech/valet drivers on brake bleeds. They use a two person team to bleed the brakes. One opens the valve the other pushes on the brakes and you hope the brake reservoir isn't sucking in air. Got my car back now and brakes feel like they were filled with air.

That was the siren call for me to pull the trigger on brake bleeder. Did it myself and I saw a bunch of bubbles come out. Needless to say just DIY.

Leave the big stuff to the dealer. Small stuff DIY.

Just dump the extra brake fluid into a aluminum pan filled with kitty litter and bag it up. Done in an hour or two.

 

FTR

DOT 3, 4 and 5.1 brake fluids are not lifetime fluids...and neither is our transmission fluid.

 

You can tell when it need a fluid change. I used to stick to 2 years. But now I will just go by feeling. I barely touch the pad as is. I think 60 to 80% life left. Original Pads with 98,900 miles now.

 

I'd personally not even consider touching it, until seeing evidence it is needed.
I've not ever seen such evidence in any car I've bought new, starting with my 1979 Corolla.
I've replaced brake fluid in cars I bought used, but again only if seeing/feeling a problem.

I bought an Olds minivan new in 2003, and sent it to the junkyard 13 years later with 190K miles on it.
It still had original spark plugs, original brake fluid, and even original coolant.
The engine still ran like new, it still braked like new (I had done pads and rotors a couple of times) and the van still averaged 26.1mpg as it always had.

Normally I do drain, fill, and bleed coolant, certainly in all my Toyotas.
And I drain and fill the eCVT trans fluid also.
About every 5 years or 100K miles. Sometimes more, sometimes less.

The Olds was a special case in that my specific car/year was delivered with both an oddball coolant, and had a tremendous number of anecdotal reports of replacing the coolant with its official replacement (which had changed) and then blowing manifold gaskets, requiring engine work. So I decided to run the original coolant until it turned to jello, which never happened.

If a mechanic who is totally trustworthy is a bit OCD about some stuff, and does the job meticulously well, it is OK to pay for some extra work to follow his advice and keep him happy and loyal to you as well. But a dealership is rarely any of those things. Their standard procedure is to ramp up what they suggest you let them do, until you push back and just say no.

 

The fewer times a stealership touches your car, the better, is my attitude. I'd prefer to only have the car touched by my favorite tire shop, and myself. I had a windshield shop replace a cracked windshield, that's not a DIY job.

I hesitate to even get my state car inspection done at a dealer, though I have found that my nearest Toyota dealer is both stringent and helpful about flunking the car for minor stuff but allowing multiple free reinspections, despite their internal billing making it a loss for them. Basically they do it to build goodwill. And it is working, if I every need work I can't do myself. So far, I've done all the (small amount of) work in the first 87 months and 133K miles since new. I even declined the free oil changes, etc. I programmed the car to accept a factory-new replacement fob when I lost one. I did pads and rotors on all 4 corners. I replaced the 12V with a bigger one very recently. I added a catalytic converter guard.

 

Problem with those testers is they are only looking for water content. The test strips, on the other hand, are looking for signs of corrosion, and early enough to prevent major damage. Personally, I wouldn’t trust the pens (seen several that didn’t even work when I knew the fluid was contaminated).
Phoenix Systems sells a double ended one so you can test your coolant too. Both tests are extremely simple. I had brakes seize up in the middle of a rush hour traffic, due to bad fluid (that had recently been tested by a mechanic that used one of those pens). Once was enough to never want that experience again.

 

Corrosion is a chemical process, in order for that to happen the correct conditions need to exist. Water content in your brake fluid, in high enough concentrations would allow for corrosion to happen. The other issue is sludge build-up. A 30 year old brake system is purely mechanical with a vacuum enhanced braking (brake booster). There could be plenty of rust in that old system, unless something blows out or you take it apart - you won't know. You can look at the base of your brake reservoir in that old Toyota, I'd bet there's a bunch of sludge down there.
The question here is, how will that sludge affect your modern brake by wire system. Will the pump and/or valve assembly need replacement; or would it be more prudent to test and/or flush out every 5 years?
I do agree with you that $300 is excessive and test equipment does break, if not taken care of properly or validated once in a while. That's a user responsibility to keep theirs tools and test equipment in proper working order.

YMMV

 

I have doubts about a cheap brake fluid tester I bought in the past. It probably was reasonably accurate initially, but it appeared to lose accuracy over time. I personally feel it is not worth it to replace the brake fluid as often as the dealer recommends, but if the tester starts giving results with lower percent moisture number over time, either get a new tester or just replace the fluid. My 2013 prius C hasn't had a brake fluid replacement since 2018 and it sill has 10 ppm copper and < 2% moisture according to test strips and my questionable pen tester. My 2020 Prius Prime got even better results. I was planning on getting another brake fluid exchange on my 2013 Prius C again some time this year, but this conversation inspired my to buy another one of my 6 dollar pen testers to compare the results to the old tester. I also bought OP's 13 dollar tester for extra comparison. I feel 20 dollars in testers is better than shelling out a few hundred dollars to a dealer. I feel like the more time a technician touches my car more than neccessary, the greater the probability for something to go wrong.

Here is my Amazon review of a cheap 5 dollar tester.



twinhealthnut
2.0 out of 5 stars Mediocre Accuracy
Reviewed in the United States on November 20, 2023
Number of Items: 1Verified Purchase
In May of 2022 I used this to test the 2.5 year old original brake fluid on my 2020 prius prime and 4.5 year old brake fluid on my 2013 Prius C that was previously replaced on 2/3/2018. It said my 2.5 year old brake fluid was <1% moisture and the 4.5 year brake fluid was < 2% moisture. I also ran it under water and it lit up like a christmas tree to the highest level of >4% moisture. Thus, I though this product was reasonably accurate.

However, I tested the now almost 6 year old brake fluid on the Prius C today and 2 months prior. Both times it said 0% moisture. I don't think it is possible for brake fluid to get better over time. However, the tester still lit up all the way when running it under water.

To test it further, I weighed 9g of brake fluid and mixed it with 1/8 tsp of water. If the brake fluid was really 0% water, which is doubtful, this resulting mixture would be 6.5% moisture. It did still light up all the way to > 4% moisture. I then mixed the resulting mixture with 11g more brake fluid, which would be a hair over 3% moisture, again assuming the brake fluid was actually 0% moisture. The tester said it was less than 3% moisture. I then added another gram of brake fluid to the mixture, which would make the resulting mixture ~ 2.8% moisture, again assuming the brake fluid was actually 0% moisture. The tester said it was less than 2% moisture. Thus a feel like the tester is now probably 2 percentage points off, because it is much more likely that the brake fluid is closer to 2% moisture, like it was 1.5 years ago.

I am not sure why this product is performing differently now. The results seem consistent, just not consistant with the results from 1.5 years ago. If you are debating on replacing 2-4 year old brake fluid or waiting a year or two, I think this product may give you useful information. However, I question its ability to give consistent results over time.

 

I just tested my brake fluid with the same tester that OP used.

2013 Prius C: 7 year old brake fluid was 2.5% moisure. I will likely replace it at it's next oil change in a couple of months.
2020 Prius Prime: 5 year old original brake fluid was 1.4% moisture.

On the prius C, both of my cheap $6 testers were showing < 2% moisture and would sometimes oscilate between <1% and less than 2%.
Test strips showed 10 ppm copper on both cars.

I feel the soft rubber cap to the brake fluid reservoir on the prius C is probably less air tight than the hard plastic screw cap on the prius prime.