100+ miles and No change on Fuel Indicator

[priuscat]

We frequently get to 150 miles before the first bar drop registers. Then it's something like 50-100 miles to the 2nd bar drop. As the tank gets lower, the bar drops occur more frequently.

It is odd, but it all evens out in the end. We have maxed at 525 miles on a full tank of gas, a few months ago. We tend to top it off anywhere below half empty.

[MrBook2]

I have been keeping track of the non-linearity of the gas gauge over my last few tanks, writing down on a notepad when the pips disappear. (I count down, so when I say the tenth pip, I mean going from full to 9 pips left.) After six tanks of gas, the tenth (or first depending on how you count) seems to disappear after a little over 140 miles. The next several pips (9-6) each last between 20 and 30 miles on average. Pip number 5 seems to last longer (sometimes twice as long) and then the remaining pips (down to 2, I always fill up by then) also last a bit longer than the earlier ones. In table form:

Pip number - Miles for pip - (Stdev) - Number of points averaged

10 - 143.5 mi - (35.25) - 6
9 - 23.2 mi - (6.22) - 6
8 - 32.8 mi - (8.44) - 6
7 - 28.8 mi - (4.32) - 6
6 - 35 mi - (9.11) - 6
5 - 39.25 mi - (16.2) - 5
4 - 42.24 mi - (13.26) - 5
3 - 64 mi - (---) - 1

There is quite a bit of variation, and this only covers a little over a month of driving (mostly in Michigan, with a mix of in town and highway) but as a general rule of thumb, I assume that after the first pip goes, all the other pips are about 30 mile (except for pip 5 which is higher) when I am trying to figure out when I will need to gas up. The standard deviation is pretty high on some of them (there is quite a bit of scatter) but I intend to keep track of this.

Yeah, I know, this all seems a little carried away, but I wish the gas (guess) gauge were a little more linear. I suspect that the first pip taking so long is actually done on purpose, to make you feel good. It makes it seem like the car is going to go forever if you fill up and the gauge doesn't budge for over a hundred miles. Same thing with the long pause at half. Can't prove it though.

As for the subject of temperature and its effect, have a look at this table:
http://www.aridtech.com/articles/art5_6.html
If you filled up your car at 30F with 10 gallons, and then moved the car to a place where it was 110F, you now have 10.6 gallons. However, this represents a huge chang in temperature (80 F) and a more likely scenario would be more like a change from 60 F to 80F in which case you go from 10 gallons to 10.1 gallons. Since the prius has an 11.9 gallon tank (or so they say) each pip should be 1.19 gallons if it were actually linear. A change of 0.1 gallons is still on 8% of a pip. Of course all of this is somewhat moot since the "tank" is really a bladder that changes with temperature in a way that is completely unknown to me. If Toyota were smart, they would make it mimic the way gasolines density changes so as to not have an overpressure if a full cold tank is moved to a place where it is warm.

Sorry for rambling for so long, but I have been thinking about this for a while now and you caught me in a talkative mood.

By the way, I am new here (06, package 3, seaside pearl.)

--Aaron

[NuShrike]

How many of you have watched this in your previous vehicle?

I did and my old '96 Civic did the same thing. Needle didn't move until past ~125miles, depending.

As I understand it, pretty typical of most vehicles out there, especially if you fill it to the top and a bit more.