when to fill up?

I've been filling up at about 3 pips just as a rule of thumb. I don't see any problem with waiting until 1 pip as long as you get gas shortly after. I think the thought about filling up at half a tank is based on limiting the amount of air space that could trap water vapor, but I don't know if that really is a factor in a gen 3 Prius.

 

ummm...well, half a bar i guess since its only on half the time... there is a DTE on the trip display... i drove 120 miles past the blinking bar...60 miles after DTE hit ZERO...

should you do this?? up to you.... the blinking bar probably starts when tank is about 12% full. Toyota does this to put the "fear of walking" into you...now if you are an exercise nut, this might not impress you

 

I believe the manual officially says that going below 1/4 tank can damage the fuel pump or something. (Cooled by fuel or something like that.) At least to the best of my recollection.

Prior to 2010, there was a bladder in the gas tank that was supposed to nicely shrink/grow as the tank was emptied/filled to keep evaporation to a minimum, but it could cause problems in cold weather where you "fill" the tank but end up a couple of gallons low. Which turned "gas gauge" into "guess gauge", evidently. So some refueling advice you see may be based on those years.

Personally, I used to run my Subaru until the yellow light came on, which never made my wife happy. With the Prius' great mileage, running down to 1/4 tank is something like 400 miles, so it's really not annoying to refill "earlier" than I used to, gauge-wise.

Not sure how seriously to take Toyota's warning about going below 1/4 tank. (It may be a leftover excuse from the bladder days.) On a long road trip, I'd definitely be tempted to go below 1/4 if it worked out better convenience-wise to get gas or eat farther away.

 

I'm usually a 2 pip filler. But, two things that make me go past that point are...

1. My all-time best MFD is 63.2 mpg. If I'm close to breaking my mark I might push it to try to set a new mark.
2. I'm obsessed with getting at least 60 mpg every tank (which by my calcs is 61.3 mpg on my MFD). If I'm slightly below 61.3 mpg on my MFD I'll drive it a couple more commutes to try to get it to that level.

Either way, I don't drive to flashing pip. If I'm on 2 pips and I can't get to my goals within 40-50 miles I fill it up. 3 straight 60+ mpg tanks for me and closing in on #4 (and possibly an all-time high tank)!

 

At 3 pips I start looking for a convenient time and place to fill up.
Generally between 1 and 3 pips. Haven't had an issue over 50k miles on two Prius.