Prius noob here - mpg questions

You need to get gas first thing. You do not know your car yet. Your display reads 51.2 but the actual is closer to 48 mpg.

 

^^^
Agreed. Don't make assumptions that the tank was completely full, containing 11.9 gallons and that all of those gallons are usable.

http://priuschat.com/forums/other-cars/94001-gas-gauge-says-full-but-thats-not-quite-true-npr.html might be useful, even though it's a Ford engineer speaking.

 

(deleted, double post)

 

(triple post )

 

Get fuel as soon as you can I pushed mine out to 600 miles for the first time last tank and put in 11.4 gallons of fuel that is to close for comfort. I would hate to be one of those I ran my Prius out of fuel people. I usually fill up between 500-550 miles, do not think I will push it out to 600 miles again. Like the others have sad there are a few variables, differences with each car and the Constant MPG display numbers are optimistic. What kind of MPG do you get when you do the math?

 

When the Prius gas fuel gauge is on the last bar and that last bar starts blinking (there is also an initial beeping when it start blinking), the Prius has slightly more than 2 gallons of gasoline left. The Prius onboard computer is normally about 3 mpg overly optmistic (sometimes it can be off by as much as 5 mpg) so if the MFD says you have sofar average 51 mpg it suggest that you are probably getting about 48 mpg when calculated at the pump. This suggests you have an rough estimated 96 miles (2 gallons at 48 mpg) before you run out of gas assuming uniform driving conditions ( The Prius MPG can drop like a rock in traffic jam lasting over 15 minutes - if you use the cabin climate controls, e.g. Heater, defroster, Air conditioner, while sitting in traffic.). Therefore, if the last gas fuel gauge bar started blinking 467 miles on your trip odeometer that suggest (if your driving conditions donot change) that the Prius will likely run out of gas about the the time when the trip odeometer reading is getting close to 565 mile. Given your current performances of 48 mpg for atleast the last +9 gallons, you'll need to improve your fuel efficiency on the last two gallons of gas to 70 mpg to achieve 600 miles on this current tank. From testimonies that I've read sofar, people drive very fast on the LA freeway and getting +55 mpg is unlikely. While one can drive the Prius past the 0 miles to go point, it is not advisable to allow the fuel tank to go completely empty because it puts added mechanical stress on the fuel pump and could shorten its lifespan.

hope this helps

Walter Lee
(aka "HyperDrive 1" on Cleanmpg.com)
2010 Toyota Prius III, Blue Ribbon/Dark Grey, oem floormats
Yokohama Avid S33D(50psi/48psi)
ScangaugeII (Fwt/AVG, RPM, SoC, GPH)
grill blocking (100% top,100% bottom)
Odeometer +18800 miles, overall 60.9 mpg
best tank 70 mpg
worst tank 52 mpg
last tank 58 mpg

 

Actually the TRUE gas tank capacity is over 11.9 gallons. Probably close to 13.5 gallons. When you fill your gas tank when the pumps first clicks off you can still put in about 2.0 gallons of gas which would fill it up to the brim / filler neck of the tank.

I know this practice if not normally done during routine fill up but
that would be your TRUE gas tank capacity.

alfon

 

Why do people always try and second guess the car? If it says get gas then go get gas. I don't understand why people play these games. It's not like you live in Australia and have to drive hundreds of miles between gas stations....

 

The problem with your assumption is that you assume you will get xxx more miles with xx gallons left in the tank despite your mpg being variable. Even if you average 50mpg over the course of the majority of the tank, you last 2gallons could be used while you're only getting 30mpg due to current conditions. Itis always best to just refuel at 1/4tank or when. The car alerts you to do so. Trying to second guess the car is just asking for trouble.

 

I think the 2010+ models may be more predicable in this regard, but just because you got 500 miles (or whatever) on the last tank, don't assume you will always get 500 miles. It don't work that way. :madgrin:

 

I've found 0 to go to mean between 9.5 and 9.8 gallons first click.

I don't push it, but because of the buffer and the car's fuel economy I don't sweat DTE 0 and can wait for my next convenient opportunity.

 

Follow up: I found my receipt for the aforementioned fill up. TripA 600.1 miles, Cons. 55.8 MPG, my calculated MPG 52.56 MPG, fuel added 11.417 Gallons. Like I said probably won't be doing that again.

 

go for 600. what's life without a little risk? you can try to push the envelope, but don't forget, it will always remain stationary.

 

In any other (non-Prius), two things would be true:

1) I'd be driving it like a normal car, unaware of, and therefore not doing too much to maximize my MPG - this is usually going to translate a calculated average that includes a lot of non-optimal driving (closer to worst case mileage than best).
2) I'd have an analog gas gauge instead of a blinking meter segment, and over time would learn what "less than E" really meant for that car and my driving habits.

As a result, I'd be comfortable driving it past E, and well past the car's early fuel warning light.

In the Prius, I get nothing but that blinking meter segment on the gauge and the early warning. I don't feel as comfortable running past the warning, because a cold spell, or a different route, or having someone else in the family drive, could push me too close to the edge, and I'd never know it.

My choice is to get to my favorite local gas station as soon as reasonably possible when I see the meter start to blink.

This time, I drove about 5 miles to the station, and put in exactly 10 gallons (about .4 gallons after the twitchy pump shut off). This was my first tank, so I've no idea mow much fuel was REALLY in the car, and when it was topped off.

If they topped it off before delivery, I got 44mpg calculated in Denver - not bad for winter, a little snow, E10, and brand new tires!

 

The better gas mileage of a Prius translates to more uncertainty of remaining range. As an example, let's say mileage varies by 20% depending on external factors, and that 2 gallons of gas remain when the low warning light goes off. Now let's apply that to a high mileage car like a Prius and a low mileage vehicle like a Jeep:

Your Jeep's good mileage is 18 mpg, which means at 20% down it's 14.4 mpg. The difference is 3.6 miles. Given two gallons of remaining gas, on a good day you can drive 7.2 miles before running out of gas.

Now for the Prius. On a good day you get 55 mpg. On a bad day 20% less, or 44 mpg. The difference is 11 miles, so with two remaining gallons of gas you can drive 22 miles on a good day. With the Prius you have more than twice the uncertainty of the distance to empty.

This range uncertainty is multiplied by the fact that the Prius is probably more sensitive to external factors. Your gas guzzler guzzles no matter what, but your Prius excels only when all the factors are just right.

Tom

 

I'm with you there. I'ts been years since I drove a car that I wasn't willing to put gas in when I reached half a tank. There's no value in running a tank to empty before refilling and it only takes 2-3 minutes to fill up now that you can pay at the pump virtually every where.