Fuel Tank Guage on Dash seem Non Linear Is this True?

[JimN]

Last night coming home I had 3 pips. Starting out this morning I had 2 pips. Within 35 miles I had 1 pip. It started flashing a few miles from the gas station close to home. MFD states 486 miles, 55.3mpg. I pumped 8.378 gallons at the slow setting until automatic shut off for 58.0mpg calculated. How much gas was left in the tank? Nobody knows. That's why it's the GUESS GAUGE.

[miscrms]

Originally Posted by JimN

Last night coming home I had 3 pips. Starting out this morning I had 2 pips. Within 35 miles I had 1 pip. It started flashing a few miles from the gas station close to home. MFD states 486 miles, 55.3mpg. I pumped 8.378 gallons at the slow setting until automatic shut off for 58.0mpg calculated. How much gas was left in the tank? Nobody knows. That's why it's the GUESS GAUGE.

On the other hand this is not really unreasonable. If you were showing 3 pips, theres nothing to say you weren't right on the edge of going to 2 pips. The temperature difference of a morning start probably tipped it over the edge. If you use my estimate from the previous post of 0.8 gal per pip at 55.3 mpg you would have expected about 44.2 miles per pip. If your last fillup was similar to this one, at ~8.4 gal, you would be looking at more like 0.76 gal per pip, or 42.2 miles per pip. Lastly, your cold start AM mpg was probably lower than your 55.3 average, so something a little less than 42 miles on a pip would be expected. Given all that, 35 miles on a pip was pretty reasonable. You don't mention how many miles you traveled on the last solid pip, but based on the above somewhere around 40-45 miles would have been expected.

I'm not saying that the gauge doesn't take me by surprise sometimes too, but when you go back and look at it what happened was usually not unreasonable. I think the problem is with our perception of how accurate it should be. I've seen regular gas gauges seem to drop almost an 1/8 of tank overnight, temperature/pressure makes quite a bit of difference even without the effect of the bladder. My wife ran out of gas in our Subaru 10 miles after the fuel light came on. Other report being able to get 30-40 miles, and I've personally gotten over 20 miles. Since the Prius gets 2.5 times better mileage, all these numbers would be 2.5 times bigger to maintain the same relative accuracy.

Rob

[rwhoyle]

When it gets to two pips, fill-up!!!!