Do you need brake-fluid replacement?

I splurged on the $13 tester.

Wife has the Prius out of town just now so I can't take a reading but I'll see what it says next week.

 

I've learned that the ethanol in gas is also <> hygroscopic <>( has to look that one up).
There's a pretty simple test tube thingy to measure it too. To see it just put a few ounces of 10% ethanol gas in a glass jar and add a drop of water. You'll see the drop(s) of water at the bottom of the jar. Than if you swirl the jar around the ethanol absorbs the water and clouds up the gasoline. Eventually water separates out again. Good the test with some non ethanol gas too.

Thanks to everyone for sharing their brake fluid adventures, dealer service experiences and testing results.

 

The thing I like about this one is that it gives an actual number. It also comes with an insert that states an error range (+ or - 0.3%), a working temperature range (0-104 F), a storage temperature range, an altitude limit and a humidity limit. It makes me a little more confident that the product actually underwent some sort of testing. The number should make it easier to compare results over time. I don't know if the brake fluid in the lines would be worse than the fluid in the reservoir, so I plan to change when it gets anywhere remotely near 3%. So far, it seems to last about 7-8 years on my prii in Southern California (not right on the coast), assuming these testers are valid.

 

Unfortunately I just tested the 7 year old brake fluid in my 2013 prius C again with the same product and it is now saying it is 2% water. I don't see how it went from 2.5% water 4 months ago to 2% water today. I guess it says the error range is 0.3%, so if the fluid was truely between 2.2 to 2.3% water both times, both tests could have been valid. However, I am a little suspicious because I have had this problem with other testser showing lower % water over time on the same fluid.

I am planning to get the fluid replaced this Saturday. That is why I tested it today. I wanted to get a test done within a few days of the replacement, so I could test the new fluid compared to the old fluid.

 

Brake fluid should typically be replaced every 2–3 years regardless of mileage, because it absorbs moisture over time, which can reduce braking performance. That said, $300 is steep—independent shops often charge far less. Check your owner's manual for Toyota's recommendation, but many mechanics agree it’s a good preventative step.

 

A small bottle of DOT3 is pretty cheap. Crack open a new bottle and see what your tester is reading.

 

That's I good idea. After reading this comment, I bought a 12 oz bottle of Prestone DOT 3 Brake Fluid this week at WalMart. Just opened it today and immediately tested it. Then I tested the 7 year old brake fluid in in the 2013 Prius C. Both were 1.6%.

 

I've never weighed in on this. Regarding the title question: somewhere around model year 2014 Toyota Canada began saying to replace brake fluid every 48k kms (~30k miles) or tri-yearly, whichever comes first.


(Toyota Canada Maintenance Booklet excerpt attached)

OP says dealership asked for $300 USD for this service. That's mildly preposterous; $100~150 USD would be a fair price. That's the going rate in Canadian funds up here, lol.

There's a link in my signature regarding DIY brake fluid replacement. (on a phone turn it landscape to see signatures)

 

There may be an issue with your tester. A new sealed bottle of DOT3 should be 0%-0.1%; whatever the accuracy specification of that unit. That bottle of Prestone should also have a production year/month date stamped on it too.

 

Maybe, or maybe these testers just aren't that reliable. I also wonder if different additives used by different brand brake fluids interfer with whatever process these cheap testers are using to measure the percent water.

Here are the test results on the new (sealed) bottle of brake fluid just opened today. As you can see, the other pen brake fluid tester aslo said this bottle had as much or more moisture than the old brake fluid. This pen also had the same issue at one point. It detected less moisture in the brake fluid over time. I think there is more likely to be a problem with these testers than the sealed bottle. I think the brake fluid production date was 1/29/25 based on the stamp towards the top of the bottle on the image below. As expected, there was no copper detected via the test strip.




Here is the result of the original factory filled brake fluid in my 2020 Prius Prime with the other pen tester. I forgot to get a picture with the tester OP bought, but it was 1.6-1.9%


Here are the results of my 7 year old brake fluid in my 2013 Prius C. It was replaced at a dealer in 2018 and they used valvolene fluid.




Here are the results of testing 21g of the same Prius C brake fluid I mixed with 1/8 tsp of water of water in a pastic disposable cup and stored in my garage for over a year. These are the little cups used for dressings and sauces when you get food to go. The lid was definately not air tight.

 

I contacted Prestone to see if they could provide any more insight. They confirmed your statement about the % water in unopened brake fluid, as well as my suspicioun about the accuracy of pen brake fluid testers in general. See their statement below

"Those Brake Fluid moisture testers are highly in accurate. The Prestone bottle you mentioned was produced on the 29th day of 2025. All Brake Fluid productions are thoroughly tested to ensure moisture is below 0.1%. We have tested many different types of % moisture testers and historically they have not been accurate. I am not sure what is causing the inconsistencies. If you are looking for a more accurate way of measuring Brake Fluid life we would have you get Brake Fluid Boil Point tester. These are found to be more reliable but can cause some false readings too."

 

did your invoice state flush or replace????
If the invoice states replace, It could be a simple turkey baster fluid removal and refill. It's still better than nothing, but was it really worth $225 for "being jobbed"? Could've done it at home for a few bucks.

 

Sorry, just asking because they charge $200+ for putting fuel injection cleaner in your fuel tank or blowing a can of anti-fungal down your HVAC system. They're certainly not removing your injectors for that kind of money..........
Brake fluid is pretty clear, If it changes to an amber color within 30 days; it's more than likely mixing with the darker old stuff in your system.
A few years ago, I was roasted on this very forum - because people seem to think there's no difference between a brake system flush and a turkey baster job. Actually saying they were the same thing and using a turkey baster wasn't fraud, when the invoice clearly stated that they did a brake system flush. Those are usually those independent shops that advertise brake service for $50-$75 bucks, actually using a turkey baster. Brake service can be defined as anything the shop calls it; whereas brake system flush is pretty clear what they are suppose to be doing.

 

In my past, I've successfully used something called Vag-Com to use the abs pump to bleed my old VW. I also successfully used a pressure bleeder. The integrity of the system was never breached though.

On a previous MINI, I had problems getting the bubbles out on one wheel, again, with no system breach, with two types of vacuum bleeders. I bought a pressure bleeder, but then talked to the local mechanic who suggested gravity bleeding. It worked great.

My question is, would gravity bleeding work if the system were breached, or is using the ABS pump via a bi-directional obdc tool the only way?

 

Just baste out and refill the reservoir? I highly doubt that. They would likely do a thorough brake fluid replacement with Techstream.

The Repair Manual outlines both a with and without Techstream method. The latter can be relatively easily done by a careful do-it-yourselfer. I've done it twice now (on our 3rd gen), car in Invalid Mode, had my wife help push the brake pedal. Takes about an hour for the actual procedure, and for me an extra hour raising/lowering the car and removing/installing wheels. Theoretically I think it could be done with wheels on, car on the ground, but much more awkward.

That said, a fair price would be up to $150 USD.