Consumption display misleading?

Unless you actually pump in 12gallons, your math is off.

Take distance traveled divided by gallons pumped in. This only works if you filled it completely up the time before, and the fillup for math was for a complete fill.

You should get a blinking light with 2+ gallons left. If it told you to add gas when there was none and had no reserves, people would not like that.

 

That's not how you do it.

Divide the distance actually traveled between fill-ups by the number of gallons you put in the tank at the last fill-up.

The consumption display is supposed to show actual fuel consumption, whether you have the AC on or not has no effect on how it works other than the AC resulting in a bit lower fuel mileage number.

The consumption displays in Gen III Prii are typically 5 or 6% optimistic.

The calculations have nothing to do with tank capacity or miles to empty.

 

How many gallons do you put in at each fill-up?

To calculate mpg just divide miles driven since last fill-up by gallons added.

 

This forum is filled with threads about the MFD inaccuracy. I fill my tank each time and calculate my mileage. I have consistently seen a 2.1 mpg discrepancy since the car was new. I have around 24,000 miles on it and have calculated every tank, to check.
You're still going to get fantastic mpg if you let the car teach you.

 

Do you actually run the tank dry, stranding the car? If not, you don't really know if you are close to empty. There is a lot of built in margin so that you cannot run out of fuel and claim that you were not warned.

See my other recent response in Fuel?

 

When you pump gas in your Prius when the pump first auto clicks
off you can still nurse in another 2 gallons until the gas fills up to the top of the neck.

The tank on your Prius is quite possibly more like 13 gallons from bone dry to completly full to the top of the neck.

Also the computer mpg guage is always off by 2.5 to 3.5 miles per gallon.

alfon

 

Note that this (while always bad advice) is extremely dangerous in a GenII (2004-2009) because of the bladder system. When the pump says it's done, believe it.

 

Also you may wreck the charcoal canister that filters the fumes, by overfilling. This would be a somewhat unfortunate outcome just to fill an extra 2 gallons that the Prius was not designed to hold.

 

It's not "150 miles to empty". It is "150 miles until you need to fill up very soon". There is no law saying you can't fill up now. Did you start with a full tank that YOU pumped? If so, then go fillup tomorrow and calculate it. If not, then fill up and wait another few weeks until you need to fill up. Unless you start with a full tank, you can't make the calculation properly.

 

The Trip A/B MPG display takes everything into account, then (unfortunately) inflates the reading by a few percent.

The 'Distance To Empty' makes a guess based on the your history, and doesn't count the last couple gallons. That is a built-in safety margin, allowing for major forecast errors. Fuel consumption is very highly variable, especially in the short term, and there is no way the car can possibly predict when it will face nasty gas-guzzling conditions, such as rain, mountain climbs, and short trips on cold mornings.

This sounds perfectly normal for my tanks that produce 50 mpg at the pump.

 

As others have said, the MFD is off. My personal experience has it about 3 MPG too high based on simple math at fill-ups.

 

I started using the fuelly.com site to track my MPG. The display usually reads around 50-51 MPG at fill-up but as you can see in my handy-dandy fuelly.com signature banner the calculated MPG is about 48MPG overall. It is always 2-3MPG lower than the displayed value.