I always get hustled at the dealer to buy a $300 brake-fluid replacement, even though the car has only 37,000 miles. This is not mentioned in the Toyota maintenance manual. Is it really needed?
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.
The only thing in the Prius Prime maintenance manual is this: Inspect power steering fluid (if equipped) and brake fluid level/condition [every 15,000 miles].
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.
That is exactly what I am worried about—it is going to be worse with more moisture and air afterwards than not letting them touch it! I should probably wait until it is six years before I do it. I could buy one of those moisture sensors as it was suggested here. Incidentally, they also hustle me for a $300 traction-battery cooler fan service. It is an owner-maintenance item that takes only five minutes. And there was no dust whatsoever on the air filters when I did a few months ago.
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 have ordered this and will give it a try: Kaiweets brake-fluid tester pen with corrosion-resistant probe
Using the brake-fluid tester above, my four-year-old DOT 3 brake fluid showed 0.5% water. I am guessing it will be good for at least another four years. This debunks the biannual brake-fluid-change requirement. In fact, I know that if I let a technian touch my brake system to change the fluid, air, dirt, and moisture would get in there. Note that you need to remove a weatherstrip and cover to access the brake-fluid reservoir.
