Fickle Fuel Gauge or Shrinking Fuel Tank?

[goldenpanda]

When it started to shudder I knew I was running on vapors. With precious little energy left to get to a gas station in the Nevada desert, I let my Prius slow gradually from its 65mph cruise. My display read 478 miles, 47.1 mpg.

The mental battle had begun way back, when Add Fuel came on somwhere over the Sierra Nevada Mountains, just 400 miles after I had topped the tank. I never had a car with a reliable fuel gauge, but I always knew the tank capacity of any car I drove. 11.7 gallons for the 2004 Prius. The fuel computer had proven itself over 8000 miles of driving -- I could make it to 500 miles with a gallon's reserve left over. It would have been insane to add fuel now.

The engine sputtered for another moment before giving out completely. Amidst the silence of the cabin I was told in big, threatening, red letters there was a "Problem!". Even now, reporting in its methodical, measured way, my Prius car was not jumping to any conclusion that I had afterall run out of fuel.

Just two bars on the battery! Where did the juice go? I just came out of a long climb over the Sierra Nevada Mountains. Was it making room for a expected descent?

No descent was to be had. I had slowed way below the flow of traffic. Instead of using my flashers the only thing that occured to me was to take the break down lane. Alas, the lane was too narrow forcing my left side to vibrate over the bumps. I figured it was costing me too much energy and swerved dangerously back onto the driving lane.

I took my first exit with only a vague belief I saw a sign for gas. Just as I took the turn, I saw the gas sign for the NEXT exit. Oh well, would never have made that far anyway.

Incredibly, with what was left of my coasting speed, a single bar of energy got me up a torturous, under-construction off-ramp, over an overhead pass, and accelerated back from a red light stop to arrive at the Union 76. The display now read 480 miles.

I checked that the gas station was indeed level as the eye could tell. My Prius car took in 10.035 gallons from empty. Indeed I had the shrunken fuel bladder. It was 55 degrees, not freezing cold but colder than last summer -- when Add Fuel came on back then I could put in 10 gallons.

Yet one more way in which this car isn't like any other. I won't ignore the fuel gauge again, at least not in my Prius car.

[efusco]

Very dramatically and poetically presented!

Word on the street is that there is, with a completely full tank, supposed to be 11.9 - 1.5 = 10.4 gallons of usable fuel.

But as you've convincingly shown, there are confounding variables. Many of us have experience early pump shut off before the tank is completely full...since you're not supposed to 'force in' any additional fuel after the pump auto-stops you may not have completely filled the tank. As you mentioned also, there is the bladder shrinkage/expansion issue.

It is clear that one should not push their luck too far in the Prius, esp. outside of heavily populated areas with a gas station every other block.

I've, knock on NiMH, never run out of gas, but I've never pushed more than 50 miles beyond the 'add fuel' warning....that said, I've also never gotten in more than about 9.5 gallons of gas, so I'm probably not using the full capacity...and that's after having the fuel guage and filler tube TSB work done.

[DaveinOlyWA]

neither have i gotten 10 gallons in, but i dont feel the need to stretch the tank. i have even refilled at 4 bars in anticipation of a long trip so i wouldnt have to get gas somewhere else.

the only car ive had with this kind of range is my other current vehicle. a ford f150 with dual 18 gallon tanks. but i would have to take out a loan now to fill the thing. besides i quit using the other tank years ago in order to save gas by not carrying the extra 150 lbs or so.

[john1701a]

> My display read 478 miles, 47.1 mpg.

Plan on 9 gallons for non-emergency use.

And take advantage of the Multi-Display providing another meter of when to plan on refilling. Of course in this case, you went way past what it would have indicated...

40 MPG = 360 miles
41 MPG = 369 miles
42 MPG = 378 miles
43 MPG = 387 miles
44 MPG = 396 miles
45 MPG = 405 miles
46 MPG = 414 miles
47 MPG = 423 miles
48 MPG = 432 miles
49 MPG = 441 miles
50 MPG = 450 miles
51 MPG = 459 miles
52 MPG = 468 miles
53 MPG = 477 miles
54 MPG = 486 miles
55 MPG = 495 miles

[rocketman7]

My trip odometer is currently reading 504 miles and I'm still on the last bar (not blinking yet). I've got a 23 mile drive home so it will probably start blinking soon. BTW, the indicated MPG is 51.8 MPG.