Featured Empty Tank Not Empty?

i think the o/m tells you how often the gas needs to cycle through. when i had my 2012 plug in, i just added a couple gallons at a time based on my usage. that keeps it fresh.
and i'm sure the 2021 system is much improved.

 

A member here did that well over 50 times, as parts of a wide variety of engineering and curiosity tests, over three different Prius generations, and reported the results back to us.

I was not all disturbed by his findings. While not pushing my own Prii as far as he did, I did use his results to run my tank down to less than a gallon remaining. Not all at once on a single try, but gradually increasing the tank depth when circumstances were benign and comparing refill quantities to the claimed tank capacity.

I have intentionally tested two cars to fuel starvation, including my current Subaru. On the latter, I got very lucky by wussing out at the last fuel station for a considerable distance, not sure my 2-gallon spare can was enough to get to the next convenient station forward, so pulled up to a pump, and the engine sputtered out as I reached for my fuel log book. Rounded to the nearest 0.1 gallon, the refill quantity perfectly matched to published vehicle specs. I must note that this vehicle has significantly less built-in fuel safety margin than the Prii I once owned, but more stages of more attention-grabbing low fuel warnings.

 

(1) Read the Owners Manual, it says how frequently you should add fresh gas. IIRC, around 5 gallons fresh gas per year.

(2) Read this oldie but goodie:
Autoblog: How desiging the Chevy Volt's sealed gas tank brought automakers, CARB together

 

Not an issue for me because I did my homework before purchasing. I go through at least a tank a month, sometimes two in the summer months.
I tell people that don't fill-up >90 days apart; to only keep a half tank of gas. That way they always have an option to top off with fresh stuff. These new car fuel systems are closed loop, probably tighter than a gas can.
You should ONLY fill-up when your road-tripping.