Fuel Meter Inaccuracy: 7k+ miles of Data

I think that is about where I am right now. I used to feel 5.6% was closer but lately I have been just under 5%. I've also been stopping at a single click rather than two which used to be the norm.

 

The other day I let mine get to where the last segment started to blink. I was thinking " better get fuel soon you are about to run out!" The "trip to empty' meter read 23 miles. So I pulled in and filled it. Lo' and behold it took 9 gallons to fill it up, not the 11.5 gals +/- I was expecting.

Guess it's good the gauge is pessimistic but that seems like a heck of an error to me. I could have potentially gone almost another 150 miles before it really ran out.

 

So far I have ranged from 1.3 to 7.8 percent optimistic readings. An overall average of 5 percent. Just sucks to have a great tank for bragging rights taken away by loosing a couple miles per a gallon.

Not a computer gamer, so the Prius and Fuelly is as close as I get to having some of that fun. Sort of fun to try at this time of warmer weather being ahead of the bell curve on Fuelly with other 2012 owners. I am looking forward to the colder months to see how my new driving techniques of the last few months translates to reduced mpg's.

 

Hi SageBrush,

Thanks for the info. I'd rather be safe than sorry so it IS a good thing there is something left in the tank when it starts to warn me to get fuel. My mileage is all over the place so I can't count on getting close tot he same mpg per tank as you, at least now I can trust the gauge and drive accordingly.

Regards

 

Once the last little pip starts blinking at you, on average how many gallons are still left in the tank?

Any possible damage by pushing it so far?

 

now you know why i post both #s in my sig

 

For myself as noted above I found I had all but 3 gals. in the tank once it started to blink. Yours may be different no way to tell unless you fill it up as soon as you can and see how much you added.

Any car with an electric fuel pump isn't helped by running it dry. It can potentially seize the pump or at the very least damage it. The fuel not only cools the pump, it lubricates it.

 

Several tanks on Trip A here are the results

Trip A : 5,111.5 Miles
Average Speed: 40 MPH
Indicated MPG: 54.6
Calculated MPG: 52.289
Gal's used: 97.753
Gas Type: Regular unleaded various brands Costco etc. with 10% Ethanol​

For a while I thought the MPG gauge was over reading about 3 mpg​

but it looks like its about 2.31 mpg over read instead. At​

least according to Trip A.​

​

​

Read more: http://priuschat.com/threads/calculated-vs-computer-mpg-please-post-your-results.65053/page-43#ixzz20c9dmLEe​

 

So you are saying you had over 7 gallons left once the very last pip started to blink?

 

Uhhh the proofreader had the day off..." I had 3 +/- gallons left when the thing started to blink!" P~

 

Gotcha. So in other words you could probably drive 120 miles or more once the last pip starts blinking, correct?

 

It would be a good idea to check your own cars fuel gauge be refilling when your gauge just starts flashing or the miles remaining goes to zero.

Gen III Prii commonly take right about 9.6 gallons when filled to 2 to 4 clicks right after the last bar starts blinking. 11.9-9.6 = 2.3 gallons in reserve. I frequently go to 0 miles remaining and mine takes a hair under 10 gallons then.

If you want to go past 0 miles remaining, reset the trip odometer when miles remaining hits 0 and then you will have a good idea how much of the approximately 2 gallons is remaining.

 

I have found out that when filling up on slow speed you can still
put in another 2 gallons of gas up to the filler neck with
standing fuel.

I do not recommend this in common practice when filling up
due to the emission control system possible be impacted
by the vapor control system.

But,if you want to know what the real full tank capacity is I am sure
it is somewhere a little over 13 gallons.

 

Alfon; i am surprised you would even mention that. it is HIGHLY not recommended one do it one single time

 

Yep that's what I drew from that leftover fuel reading. But the " Miles to empty" was telling me only 23miles so I scampered in and got it filled only to find 3 gals. left!

Better to be safe than sorry I guess, no sense pushing it just so I can brag I got 'x"number of miles to a tankful.

Cheers

 

I can't pump my own gas in Oregon and there is a law or a violation of law if you
pump beyond the first pump click off. Also in summer with warm temps filling
that way may be an issue more so than in winter.

I do not recommend filling your tank this way, but just to point out that
the true maximum tank capacity is more than 11.9 gallons.

 

Another easy way to compute your range is to multiply your "displayed" mpg value by 10. It is a simple calculation to do and will give you confidence that you can make it that far without running out of gas. You could treat that value as your Miles at empty value (and still have a decent reserve).

Thus, if your displayed mileage is 50.0 mpg, your range would be 500 miles. With that 50.0 mpg, you are probably getting 47 - 47.5 mpg (actual). If we assume 47 mpg and divide it into 500 miles = 10.6 gallons. You would still have a 1.3 gallon reserve, thus if you got an incomplete fill up, so long as it wasn't over 1 gallon, you should be fine.

 

So far my comfort level has been one bar or at the start of the blink of one bar. For the way I fuel my Prius this works out to 9.5 to 10 gallons. Even with the higher mpg's I am reluctant to try to work that last 1/2 to 1 gallon.

And after the derecho we had this way recently I am reluctant now to let the tank get too low. We were fine in my household, but others around here weren't so lucky.

Between the earthquake last August and the drecho this month, feeling safer in having 200 miles of gas in the tank.