If I understand your post, then the "miles till empty" number would be exactly the same on every fillup. It's not, so how is it determined?

 

The computer uses a best guess at your expected mpg based on medium term driving habits, I don't have any exact formulas but I don't feel this exactly mean last tank, as you could fill up every 3gallons and count as a refuel; and I don't think it uses the user's ave MPG tracker feature either.

It will auto adjust range as it goes changing both the expected MPG and multiplying by estimated fuel left in your tank. It is not static for a whole tank.

If you scroll through, you can find screens that display instantaneous MPG going all over the place. A modern fuel injected vehicle knows exact fuel rates so it knows MPG and can estimate tank volumes. It is not hard for it to do some rolling calculations as it goes. It won't jump the Range up and down though to help the humans stay sane.. It'll only go 1way and instead pause the range countdown until it catches up and can continue the countdown.

 

That's not what I intended. My primary message was in response to the OP's wondering how his actual range could be different than what fueleconomy.gov publishes. The short answer is the gov's number is pure fantasy, and only theoretically achievable by incurring damage to the vehicle. @raytseng 's description below is likely a good description of how the range is calculated.

Well described. Fundamentally, the first range posted after a fillup will likely be least accurate, and the range will gradually become more accurate as it approaches zero.

 

I dont ever look at the miles until empty. I like to calculate it manually.

I average 25 mpg on my F-Sport.

 

I assume the OP is aware the humans low fuel light and computer est. range and is set with a 2.9gallon reserve?

There are other threads that explain the common reason is because low fuel will damage the fuel pump. I think this is only half the story.

Obviously gasoline is a liquid, so it sloshes around. Unless you have the vehicle on a treadmill, when you get to low fuel the real issue is the fuel can't be picked up reliability. If you are on a slope you might not get fuel at all, so they can't guarantee the vehicle will run. So this point is more about reliable fuel delivery due to gravity and liquids than just overheating the pump.
Additionally the problems are more than just the pump overheating. If it is barely picking up fuel, you could get unreliable fuel delivery to the engine. You can get misfires and surges. This is just as much of a concern. It is like for your home electrical where a brownout with power flickering is worse and cause more damage than if the grid shut down gracefully.

Anyway, if it's the zombie apocalypse, and you must drive the car until it dies, you probably could go that extra 2.9gallons x mpg assuming you're on a nice flat road.

 

On a round trip Dayton > Indianapolis > Dayton (266 miles) on Tuesday of this week, plus ~50 miles of local short-trip driving, my F-Sport got 24.8 mpg, per gas pump refill calculation. I use the radar cruise control as much as possible -- that seems to boost efficiency, for some reason.

 

That’s interesting because on my 2022 450hL cruise control *reduces* my real-time mpg. It seems to accelerate at points where I would coast or just slightly feather acceleration. I suspect that’s the reason for my different results.