Can we only use Toyota coolant?

The following link recommends either a year max (Castrol recommendation) or "a few months" (the author:

What is the Shelf Life of DOT and Mineral Oil Brake Fluid? | Epic Bleed Solutions

My thought: once you get the brake fluid level right, there is no need to save fluid. Well, unless you're going to do a brake fluid service on another vehicle in the very near future. Once you get the fluid level correct in the reservoir (say at top mark with brand new pads), there is no need to top it up, ever, unless the system is leaking, and then you have a bigger problem.

With a normally functioning brake system, with no leaks, the fluid level in the reservoir goes down as the pads wear, and then rises back to the top mark with the install of new pads. Topping-up is not necessary. The brake fluid level is actually a good indicator of pad wear.

That is a bit "clouded" on the Prius: the brake fluid level in the reservoir will drop about 1/2" when the driver's door is opened and the system pressurizes. You can pop the hood by going in through passenger door, avoid this.

Decades back I can recall saving a half-full plastic brake fluid bottle, and after a few months noticed that plastic wall of the bottle, from the fluid level downward, had hardened up. Strange.

 

kind of ridiculous because do you think the transmission, motor, and brake system are as well sealed as a bottle? They all have vents and expansion lines. Look at the cap to the brake fluid reservoir and tell me that provides a better seal against moisture in the air than a tightly screwed lid on the bottle it came in.

 

Yeah I wonder about that too. Still, for $7 a pint, and something I only use every 3~4 years, I'm not hanging onto it.

 

Sounds like the fox guarding the henhouse to me.
As I mentioned you will throw it out because the bottle looks funky before the fluid inside goes bad. That foil top is just to prevent spillage due to the top loosening during shipping. The cap itself is enough to keep new air with new moisture out. The small amount of air that is in the bottle won’t affect the fluid.

 

You may be right, but considering the minor expense, and what's riding on it, I play it conservative: fire them out.

 

That’s fine for you, I just don’t want somebody thinking they should discard whatever they don’t use immediately. Castrol might say throw it out after a year but they sell it. I can assure you it will last 5 years no problem if you cap it right away. They make sensors that can measure the % of water in brake fluid. I own one.

 

My scenario too: the only time I'm dealing with brake fluid, is when I'm changing the fluid (every 3~4 years). I'll get 2 pints, with the intention of draining/filling until it's used up. I hold back maybe 2 oz, on the off chance the reservoir level moves a bit over the next few days.

Other'n that I'm done. I have no further use for that oz or two, for another 3~4 years.