What is the lowest that I can reliably/safely run the fuel tank?

one bar is fine, but dangerous. don't run out, it's a pain.

 

The bladder is a big variable from car to car. While many owners can regularly go down to and past a single blinking bar, over the years a significant number here have reported running out of fuel when trying to do so. A small number have run out with even two bars remaining.

Without testing your own car, and taking some risk by running low (take some spare fuel along for any super-low-tank test), you really can't know. If for some reason you need better range, then do such a test, at a time and place that is both safe, and not inconvenient if or when you run out. Then set aside some of that measured range as safety margin, because future conditions will vary, especially on Gen2 Prii.

If unwilling or unable to do such a test, then keep refilling at or before 3 bars.

 

Our C-Max has a 14 gallon tank/600+ mile range; more urban speeds= 700-750 miles. My personal best was 890 miles hypermiling. Add in a plug and you can get thousands and thousands of miles per tank. You have choices.

 

The running it low advice in most cars is a hold over from the days where the fuel pump was cooled by the gasoline it swam in. When you let the tank drop too low, it got hot and could burn out. Additionally the pumps don't suck from the very bottom of the tank, there is assumed to be sediment and crap there accumulated over lots of miles. So on old old vehicles, 1/4 tank was the recommendation. Voila, 3 pips in the Prius.

You have a 2005, a Gen-2, and I assume you're in the US. So you have a bladder, not a tank. It's a flexible rubber bladder. You don't have to worry about cooling the pump and sediment isn't really an issue in the 2000's with all the filters and screens everywhere. What you do have is the bladder can fold over itself or crease. You could put 7-gal in and assume it is full because it clicks off, but it may actually just be 7-gal because the bladder filled and folded.

With the Gen-2 Prius I generally fill it up at 300-miles. I use a trip meter when I fill up. Sometimes I'll get up to 400-miles but usually just when it approaches 300-mi on a tank, I fill up the next time I pass one of my trusted gas stations.

If you don't want to fill up so often, buy something with a plug.

 

I have never gone lower than 2 pips. Never.

Over 13 years its has worked well never ran out of gas which is a real nightmare in this car and could kill an old hybrid battery. Because usually when people ran out of gas in his car they would drive on the hybrid battery to get to a gas station or drive till that battery is dead. Dead hybrid battery =no start and no way to charge it.

Saw so many of these back in the day every once in a while we still see it on here.

Hybrid battery dies hilarity ensues on your wallet. Tow to the dealer he's got to get in the 'special" hybrid charger "special" means its going to be very special on your wallet. Couple of gallons of gas could cost you hundreds of $$$$.

 

IF......you have a model with a "bladder" in the gas tank, the 3 pips might be important.
If you do NOT have that kind of tank, then one pip is fine or even flashing........IF are in an urban area where stations are plentiful.
And if you consider running out to be an "adventure" .

 

I don't know.
And I STRONGLY encourage you to get OUT of the habit of running it as low as possible.
Regardless of your model, or brand of car really, running it completely empty can sometimes damage the fuel pump.
And if you try to run it as low as possible, the odds are great that you will run OUT occasionally.
AND there is no good reason to do that anyway.

 

As far as I know the flashing one bar IS the low fuel warning. Every gen2 can be a bit different but for mine I refill as soon as it hits one bar and it takes 7 gallons without topping it off. (haven't run out in the two months since I put it on the road.)

Posted via the PriusChat mobile app.

 

The one flashing bar IS the low fuel indicator.

When it begins flashing, if the fuel bladder is fully expanded and not causing any short tanks, there ought to be roughly 2 gallons remaining. If the previous owner's experience is good, then it sounds like you probably didn't get one of the units with a problem bladder.

While some people issue plenty of warnings about running low being a hazard to the fuel pump, others seem do it regularly without consequence. One member here, Bob Wilson, intentionally ran his Gen1 completely out of fuel 50-ish times as part of his various engineering and curiosity tests, and experienced no such failure. At last word, his housekeeper was still driving it.

 

My 2005 I've driven down to one bar BEFORE it flashes then I fill it up. Usually once it gets to two bars I fill it up. The most I've had to fill it up is around 8 gallons.

Posted via the PriusChat mobile app.

 

My 04 scared me once as i started a short 13mile trip up into the national forrest near me. Figured with 3 bars i would be fine (only had the car about 3 months and was still learning the guessometer fuel gauge).i only got about 6 miles and it dropped to two bars but i was close so kept going knowing it would be downhill most of the way back into town, just as i reached the trailhead it dropped to one bar (what the heck 2 bars in 13 miles i thought) . Was worried i wouldnt make it back and so with engine warm i just turned around and feathered the throttle all 15 miles back to the nearest gas station, at about 6 miles back the info display beeped with a warming "get fuel soon" and pip started flashing(that really helped!) . Bugger it only took 8 gal to fill what was supposed to be a 12gal tank, needless to say im carefull now about heading anywhere uphill on 3 pips.
On my normal daily commute getting 50-52mpg my range varies fro 300 to 325miles per tank so im looking for gas anywhere above 300 miles now(my trip info display odo resets at every fillup). Ive had the gauge drop from 3 to 1 pip in the span of 10-15 miles twice since on level ground easy driving , so it really is a crap shoot sometimes.
Wish i could import a euro non bladder tank and fix the guessometer once and for all......dang CARB

SM-G960U ?

 

I've never had anything like this happen, and it sounds like an unusual circumstance for you. How steep were those mountains? Maybe it was a car angle issue? Since it only took 8 gal in, it does sound like you had a bit more in the tank!

 

Owned my g2 for 13 years even with pip flashing when I first bought
The car has never taken more than 8 gallons but I don’t top off the tank because did that when I first bought it got a shoe full of gasoline.

Pull into gas station uncap the gas cap let it vent for a minute then fill it
Up first time it clicks off that’s it.

Now 13 years later I no longer have to vent it it stopped that nonsense I think the bladder has worn out and moves much more freely now.
But when it was new it was a bitch to fill up. That’s in Florida it’s much worse in the cold. much much worse.

 

After the last bar starts to flash, I also get a BEEP and a message saying ADD FUEL on my MFD every time I power it up until I put fuel in it. At least my 2004 does that anyhow. I've tested and know that I get about 90 miles after my last bar blinks. 60-70mph highway miles even. crazy right? I even did the fuel level sensor re-calibration and it didn't change. So I trust it.