Odd fuel gauge behavior

Here's the skinny:

-Driving home with about 140 miles since fill-up. MFD says about 63mpg, so assuming the normal error, I've used a little over 2 gallons.

-Fuel gauge shows full minus one pip. I would have expected full minus two at this point.

-Then, after a run that was neither strongly uphill nor strongly downhill, the fuel gauge goes up to completely full for about ten minutes.

-Then, it goes down to full minus one for about ten minutes, then full minus two.

-When I got in it this morning it showed full minus three, then after about ten minutes went to full minus two. I drove another 50 miles and it is still at full minus two.

-Distance-to-empty seems to stay consistent through this period.

So, does anyone have an idea? This may be my first tank on "winter blend"... is there a possibility of foaming or something? I don't know if the Prius gas gauge is fed by a float like older car tanks, or is measured by weight, or what.

Should I be worried if this behavior continues? Has anyone else seen this?

The Prius uses a float like most cars. There is also a damping time constant to reduce rapid swinging of the fuel gauge, and also an inclinometer to compensate for grade. I suspect your fuel was sloshing around a bit as you went up and down hill. The distance to empty calculation, on the other hand, is working from calculated remaining fuel.

Tom

Nothing odd here. Not only does this behavior happen in my Prius, its analog equivalents happened to the gas gauge needle in every previous car I've had.

It's simply just not as accurate a device as you want it to be.

I'd say that's the answer I needed. I'm surprised, I guess, with all the other technological wizardry that they're using an old-school float to do the initial measurement. Oh well, whatever works.

To add to the insult, most vehicles are intentionally mis-calibrated so that about 75% of the fuel has been used when the gauge reads half full.