Gas Tank Guessing Game

welcome! you're correct about the bladder. just fill to the first click and keep a running average of your calculated mpg's.
you can try waiting a minute after removing the gas cap, pumping as slowly as possible, holding the pump handle upside down or 90 degrees, and trying different pumps.

if you go 200 miles at 50 mpg, you should be putting 4 gallons back in, right? but only if you started from full.

 

Take bisco's advice. Just fill the tank till the pump shuts off, reset the tripmeter, and note the odometer as well. Go through that tank, as low as you feel comfortable, refill the same way, reset the tripmeter after noting, note the odometer, do the math for the miles per gallon, report back.

 

bisco, does the Gen4 have a blatter or a regular fuel tank?

 

No bladder in the Prius since Gen 2

 

^^^ they realized the error of their way and engineered a way around it. probably cost 'em a few shekels.

 

o/p, the bars and the dollars and the amount of miles on a tank and the weeks between fill ups mean absolutely nothing. you have to do the math. it's painful, but like they used to tell me in school, someday it will pay off.

 

In my region, $10 of gas is less than 4 gallons. 200 miles is quite reasonable for that amount. Plenty to traditional cars won't get 100 miles for that price.

Those traditional cars will also swallow up $25-40 per 'tank' of fuel.

Your car is suffering from a small/weak bladder, but is doing just fine on MPG.

 

Why is this thread posted under Gen4 fuel economy?

 

uncertainty, that's a funny way to put it. My favorite "uncertainty" was filling the tank with a slightly acting-up fuel nozzle. You realize it's got to be full, you pull the nozzle out, and it vomits up a good half gallon or more. Good thing you're not smoking.

.

 

I have tracked a total of 10 tanks on Gen4 and 2 on Gen3 (as I had come to the idea of doing only a couple of months before selling it...).

I wrote down every so many traveled km, the DTE and the km driven so far with the tank and its related fuel consumption value.
I then calculated how many total km the MFD had been estimating at that point (i.e. current traveled km from tank + DTE estimated km) and recalculated the fuel equivalent fuel consumption, by not considering the fuel light fuel level, as per user manual (6.4L // 1.69 US gal).

As I result, I have found out that my Gen4 is overestimating range on average by 20%, and taking into account the fact that the MFD overestimates by about 4-5% in Gen4, this values lowers to 13%.
Otherwise said, whatever the DTE says, take 20% off and you know more or less when it will reach zero in real driven km.

I have noticed that the fuel light comes on typically at 50km // 30mi DTE. When DTE is at 0, and the fuel bar is totally empty, I still have about 5L // 1.3 US gal in the tank....

Gen3 was on average (albeit calculated over only 2 tanks) 22% off.

All in all, I really don't rely on the DTE indication but simply use on the amount of km driven so far, the (corrected) fuel consumption for the tank, and calculate, based on these values, how many liters I have used, that is, how many I have left in the tank.
I then use an average fuel consumption of choice, typically 5L/100 // 47 mpg (I am being conservative, in a way), to estimate how much left I have, before being forced to walk.
I have printed a table that I simply look up, to avoid calculations on my phone while driving (unsafe!).

A 20% off DTE estimation, is not too shabby. But DTE/fuel light/fuel bar are in general so conservative, that I never really rely on neither of them to know when to fuel up again (which is essentially based on logistics and "strategic planning" ).

 

Maybe just keep an eye on the gas gauge, lol?

 

I think if you fill at half tank, DTE gets even more inaccurate. IT appears to assume the miles between full-ups are for a whole tank, not what was just added.