My first fill up: 57.7mpg

You would have easily made it another 100 miles with your 11.9 gallon tank. Now you know what your mpg offset is, you can subtract a rough difference and know how far you can take your car. I think you were being too careful. Did you even have the fuel warning on?

 

Easily? I don't agree, that much would be pushing extremely deep into the safety margin. Be prepared for failure. [WARNING] Running out of gas (Gen III)

No, that is the last warning before it runs dry.

 

seven hundred or bust!

 

Probably, but how often are you happy to be wrong ? Be careful not to run down the traction battery on an empty tank. That can be painful to your car and your wallet.

600 miles on a tank that reads 55+ mpg on the car meter is safe.

Btw, if your motivation to push the tank towards empty before a fill-up is avoidance of fuel stations, consider this arithmetic:

An extras 10% miles per tank pushes you into the danger zone of running dry. The benefit is one less pit stop every 10 fill-ups. Since 10 fill-ups is about 6000 miles, you are talking about one less pit stop every 3-4 months.

 

Possible, yes, but I wouldn't call it certain. Making allowance for variations in fillups, usable portion of the tank, fuel consumption in non-ideal conditions, car-to-car differences, and sloshing and slope effects on the tank, and I can easily imagine running dry in less than another 100 miles.

In the thread linked above, Bob went 122 miles (at 56.6 mpg) past the point where the last bar started flashing, not from DTE = 0. You probably went about 25 miles from the flashing bar to DTE = 0, then another 23.7 miles past that, which is about 49 miles into Bob's distance. That leaves only (122 - 49) = 73 more miles until dry, if your conditions and car are the same as his. Adjusting for your higher displayed MPG, that makes 83 more miles. Then you need to guess whether, on the random variables, you drew a longer straw than Bob, or a shorter straw.

I have gone 90 miles past the flashing bar on mine ... on a very good MPG day, in benign circumstances where failure would not have been painful, and with a spare can of fuel along for the ride. That was far enough for my test and emergency planning purposes.

 

no way to know because it depends on how many lights and stop signs you hit, etc.

 

The earlier model Prius have an abundance of "out of gas" indicators including the "Check Engine" light. The driver can use the remaining traction battery energy, typically 1-2 miles, to find a safe place to park or reach a gas station. So when we got our 2010 Prius, I was curious to find out what it told us as I also do gasoline quality studies(*).

The first time I can the tank dry, I was driving at low speeds and hilly street on a downgrade. The "power steering" light came on so I pulled into a parking area by a park just 100 yards ahead and discovered the engine was not running. I had my safety gallon; added it, and; was off. There was no other indication that all gas was burned.

The second time, I was on a 50 mph, limited access, four lane with an access road. Only this time a slight upgrade and again, "power steering" light but what surprised me, no accelerator response. The traction battery showed charge but the car had become an inertial mass . . . just like a stupid, regular gasser. Still, I had enough momentum and no traffic so I coasted to a parking lot and added the safety gallon. But it was clear, the "power steering" light meant the car was power inert.

The third or fourth time, I was using the energy flow display making a turn onto the downgrade, ramp of 70 mph Interstate highway extension, I-565. As I made my turn, I noticed acceleration was weak and looking at the energy flow display, the power arrows had gone away BUT the car was responding to the accelerator. I still had traction battery power!

I put on my flashers and drove 200 yards beyond the end of the on-ramp and pulled safely to the right edge of the shoulder. Standing in the grass, I added the safety gallon and was off.

I contacted Toyota about this change in behavior and was told this is how they designed it. Toyota has turned their backs on an important safety advantage, letting the driver know they are down to limited distance, traction battery power.

As for 'flash' calibration, it typically means our car has 2.1 gallons remaining. However, a high-G turn or slope can induce 'flash' early. So I reset the trip meter when 'flash' starts and then track how much of the 2.1 gallon minimum remains. When down to less than 1 gallon remaining, I put a safety, 1 gallon gas can in the car. This is the most recent tripmeter when the car ran out of gas:

In this case, 2.34 gallons burned before out of gas on July 21, 2013. Only this time, I ran out of gas on a downgrade at a stop-light. I saw the energy flow arrows had gone away.

When the light changed, I drove on traction battery 0.6 miles to a safe neighborhood side street to add the safety gallon:


An engineer and private pilot, I want to know the limits. So I have no problem with doing 'the forbidden experiment' with attention to details. It doesn't mean I recommend driving to the limits but knowledge is power and gives me confidence to make the hard choices.

My usual practice is to drive about a gallon into "flash" and typically fill between 10-11 gallons. I don't use the coun-down miles but it appears to be a good metric for those who wish to 'tickle the tiger.' Once it reaches 0 miles, it is time to find a gas station.

Bob Wilson

* - In gasoline studies, I run the tank dry and add a gallon with a known mix. I used this to determine:

1. E85 - runs but raises a 'harmless' Check Engine light and poor MPG.
2. E50 - runs without the Check Engine light and not so good MPG.

 

Although I've run Prius out of gas over 40 times, I've rarely heard the stutter and I was listening for it. As for feeling it, no. The car smoothly transitions to electric power and continues to run within the traction battery limits. Unless the driver knows to monitor the energy flow arrows, running out of gas is unknown until the traction battery level gets so low that a false "power steering" indicator comes on.

You could have easily reached 600 miles. But I'm also someone who believes in having a safety gallon when running under flash. I know my car and due to ordinary differences during manufacture, there is no assurance your car will behave exactly like mine.

Bob Wilson

 

There are two locations:

• driver side, rear, insert, behind rear wheel - if you have a plastic can that fits in that location, it will hold them upright against turns and bumps. Fold the carpet over to minimize solar heating that can lead to extra pressure in the spare container than needed.
• behind passenger seat on floor - best with stuff to prevent shifting and a cover to block direct sunlight. Again, solar heating can lead to more pressure in the can than desirable putting pressure on seals, caps and valves.

I have used both but am partial to the floor behind the passenger seat because it is less exposed to sunlight.

Bob Wilson