so I just had to fill my tank yesterday for the first time. 2015 prius 2. It was on the last bar, which started flashing, so I got a bit nervous and filled it. I'd wanted to try to hit 400 miles, but when it started flashing, I didn't want to take the chance and I filled it at 382. It would only take a little over 9 gallons. That's with me repeatedly trying to top it off. I would have thought that low fuel bar flashing would mean it would have taken closer to 11.5-12 gallons. I know it's only got a 12 gallon tank, but 2.5 gallons is a big deficiency from 12. Is this normal with the prius? On the plus side, I filled my car up and it cost me $21. That would have been 1/3 tank in my old car and less distance, and about 1/4 tank in the wife's suv.
My 2 cents: fill it when it's reasonably low, no point in stretching tanks. Stop pumping when it clicks off the first time. If you want to calculate something, mpg is worthwhile.
I fill up till I see liquid fuel in the filler. I have never had any problems with emissions or whatever. If you have a GII with the bladder, perhaps some care doing this would be needed (but I always filled Pearl up the same same way with no issues). DON'T PANIC. (as per the "Hitchhikers Guide"). Now, I live in Edmonton, where the air temp is -usually- MUCH lower than the ground temp. So fuel -shrinks- after fillup. Except in the depths of Summer. It seems to me, Toyota has designed their vehicles very conservatively, allowing for a great deal of fuel expansion. The FJ Cruiser is the same. I like to fill all the way up because I get an extra 100 km range to empty with the Prius, 50 km with the FJ (and you need all you can get with an FJ - the fuel tank is TOO SMALL). I know, a little silly, considering I usually fill up at 1/2 full, but with a Prius you fill up so infrequently I like to spend extra time at the station to fill it -all- the way up. So enjoy filling your Prius fuel tank. You won't do it very often.
I typically stop when I get the first click which is typically between 8.5 and 9 gallons. I also usually stop once my estimated miles gets to around 50.
The blinking light is unsettling but as you found, they leave a large margin in reserve. I've only pushed mine once to hit just over 500 miles to the tank. If you 38 mpg is right, that will be tough but I am certain you can improve on that.
To OP, there's a very good chance the tank wasn't quite full when you drove it off from the dealer. Even though 10 bars on gas gauge, it might have needed another gallon or so to be filled up. In other words, you may go quite a bit further on your next tank and get better MPGs. btw, I usually put a little over 9 gallons to fill up also. I've never pumped in 10 gallons to fill up. I'll let it go to 1 bar usually, 1 blinking bar rarely, but I go right to the gas station.
You'll get a lot of different feedback. My opinion is that Toyota and "The Prius" IS conservative with their gas gauge. BUT My further opinion is that you did just fine. In a "non-panic" manner fill up when you get down to the last flashing Pip. If it turns out you are putting less than 10 gallons of gasoline into your vehicle...celebrate less than 10 gallon fill ups. Toyota gives you a very conservative buffer when the final pip starts flashing...but I see no advantage in really doing much of anything but filling up.
FWIW, here's what the EPA has to say about topping off the tank: Don't Top Off Your Gas Tank! | Mid-Atlantic Air Protection When at home, I fill up when the gauge gets down to 1-2 bars or starts flashing. I don't panic though because I know there is still almost 2 gallons left in the tank even when the display says 0 miles to next fill-up. When traveling, I fill up based on GasBuddy fuel prices along my route. With a little bit of planning, I generally end up filling up every 300-400 miles or so. Since we stop every 2.5 to 3 hours anyway, stopping for fuel where prices are lowest is no big deal. Granted, I don't save much these days with low prices and high mileage, but I can't seem to break the habit I started with our old 24 mpg van. If I'm going to stop to take a break, I might as well get fuel if the price is right. I save at least 10 cents a gallon doing this, oftentimes more, though that only amounts to $10-$15 on a 5,000 mile trip like the one we just completed to Florida/Georgia and back.
