how much usable fuel left

My guess would be 2 out of the 2.6 gallons left would be usable before the gas got below the suction pickup point.

One thing to keep in mind when running low on gas is that the fuel pump is in the fuel tank. It uses the fuel to cool the pump motor. If you run the fuel low you take a chance of overheating the fuel pump motor.

So, as you said, why take chances?

 

That is hard to say there are too many variables, like your actual MPG how much fuel you put in at the last filling, where you drove, etc. Some members push their cars out to 600 miles per tank and still have some fuel left maybe like half a gallon. The most I have been willing to go is about 550 when I fueled up my car it took 10.5 gallons. I think I can push it out to 600 miles per tank, but I don't want to run out of fuel. If I carried a gas can with me I would consider trying for 600 miles per tank but I don't so I won't.

PC member Bob Wilson has done allot of research on this topic purposely running his car out of fuel.

PriusChat Forums - View Profile: bwilson4web

This may not be the correct thread but it should put you in the right direction.

http://priuschat.com/forums/gen-iii-2010-prius-main-forum/64211-warning-running-out-gas-gen-iii.html

When in doubt fill up your car, other wise it could cost you some $$$$.

 

Don't take chances. Why risk having to replace the fuel pump? It's a lot cheaper to fill up your tank before you need to, than to have to have your car towed and have the fuel pump replaced. Looking at those two alternatives, I think I would fill it up with gas when it gets to a 1/4 tank or a little below.

 

Another item for perspective, even though it's a Ford engineer talking: http://priuschat.com/forums/other-cars/94001-gas-gauge-says-full-but-thats-not-quite-true-npr.html.

 

Because of possible gauging variations among individual cars, I think it better to test you own specific car to the level you could foresee needing, before you need it, and do it in circumstances where the cost and hazard of messing up and running dry is very low.

If your fuel gauge variance is one of those on the wrong side of the distribution curve, you don't want to discover this on a dark and stormy night, on a holiday, on a 100 mile stretch without services, with your mother-in-law in the car. My very first car ran dry with its fuel needle above E, but at least I discovered that on pleasant warm day, in town with parents not far away.

 

I also found in my first 5,000 miles that when my dash gauge said almost empty (not flashing) and I filled her on up I was putting in around eight or nine gallons. I'm not in to pushing things here but I too wondered about this with a twelve gallon tank. I track milage and usually get over 50 mpg's (although now in winter I'm more like 47 mpg's). I was pretty low on my way into work, according to the gauge but it is only a 35 mile round trip so I decided to see. On the way home the little light started to blink but having never had to put in even 10 gallons I decided to just drive home. When I stopped to fill up it took just over 10 gallons which gave me a warm fuzzy feeling that I still had more than a gallon left. Not something I'd do normally as the whole fuel pump cooling thing, still it's nice to know. There are probably variations to some degree from one car to another but "if" one got the blinking light I'd feel safe if need be to run 50 more miles to find gas.

 

The most I've driven on flashing pip was 75 miles and took 11.5 gal to fill up. The most I've driven on flashing pip on PHEV was just over 200 miles and that took 11.36 gal to fill up. You can go up to 50 miles on flashing pip. Anything after that, carry a spare gallon of gas or go fill up your tank.
Most Prius gets 50mpg. There are about 2 gallons of fuel left in the tank when the pip starts flashing. Theoretically, you can drive just over 100 miles before running out of gas. The fuel pump is pretty robust. Running out of gas just 1 time in its lifetime is not going to damage it. Do it frequently then yeah, it's going to fry.
If you want to push it a little, 50-75 miles at 0 DTE should be OK. Anything past that, then you're on your own. If you drive frequently on steep hills, then you should fill up your tank as soon as the gauge hits 1 pip to avoid sucking up air and damage the pump.

 

I believe the true Prius gas tank capacity is probably closer to 13.5 gallons.

When the gas pump first clicks off you can still pump in at least another 2 gallons before you see fuel at the gas tank neck.

I know this is forbidden even though it is not mentioned anywhere in the 2010 Prius owners manual.

I remember when Wayne Gerdes did his mpg tests with many vehicles he always filled up to the neck with standing fuel being visible.

I have filled up our Prius a few times like this in other states, in Oregon filling up your own vehicle is strictly forbidden, and noticed no lights or flashing bells went off. The car ran perfectly and I could smell no odor of raw gas.

just my thoughts and observations.

alfon