Fuel reserve at 0 miles DTE - some data

All:

It's taken a bit with my Prime, but I finally had enough fill-ups to try and get an idea of how much fuel is in the tank when the car claims 0 miles DTE. I've heard many folk say it is around two gallons, so a bit surprised I'm coming up with only about a gallon. Attached (hopefully) is the data I've gathered and math/assumptions, is there something I'm not doing quite right?

For each fill-up I noted the DTE number and gallons filled. The manual says the tank capacity is 10.6 gallons, so the gallons still left is just the the capacity minus the fill-up amount. I thought about trying to use the cars claimed miles remaining and tank capacity for MPG, but that ends up being circular reasoning as you have to assume how many gallons are left at 0 miles DTE again! So, while not ideal, I just assumed my average MPG of about 45MPG. I then simply took the DTE miles divided by MPG to subtract those gallons from gallons in the tank to get an estimate of gallons in the tank at 0 miles DTE.

Fully understanding this is noisy data, I wanted to get a decent number of data points before doing the math. As you can see, most of this data was all around a long (5,200 mile) road trip late last year, I hardly use any fuel around town--exactly why I got (and love) the PPPXP--Pretty Prius Prime XP.

(I haven't tried an attachment in while, so if it still doesn't work the easy way, I'll follow up with a post doing it the hard way)

will

 

@KMO: I thought I had read that somewhere in these forums, but I'm not very good at searching for stuff I'm specifically looking for.

OK, if the math checks out at least as best it can be, I'll take that info a reasonably accurate then. I've been both a "fill it up at a half tank" person and a drive it until it says empty person too for many years in a row of each. With the Prime it makes it easier to be the latter, so still mulling it over.

will

 

@fuzzy1: Nope, not that bold! At least not on purpose. To your point though, the huge assumption is that the tanks capacity is per the spec sheet. I'm suspicious of that too given that in my Gen1 Prius I've pushed my luck and put over 11 gallons into a tank that is claimed to be only 10.5 gallons. Only your suggested test truly measures EMPTY and not quite willing to go that far. I suspect there is reserve even above what they say the tank capacity is. I've seen some other posts here where Subaru and Jeep really mean it when they say 0 DTE and don't do all this reserve stuff Toyota does. The engineer in me likes that approach, but fully appreciate Toyota's reasoning too.

@Preebee: That would be interesting if Toyota picks different reserve levels for different models (Maybe not trim levels, but possibly between the Prime/AWD and not). One of my data points came close to suggesting a 1.5 gallon reserve, but that was the most extreme measurement. Gathering data is easy so I'll continue doing it. Just with a lot of city driving, the speed of gathering data is pretty slow.

For my Alaska trip in my Gen1 I was carrying around a Jerry can of fuel as a precaution, so I guess I could do the "real" test, but not that bold. BTW, even for an ICE car, range anxiety can still be a very real thing up in the far north where gas stations are easily if not mostly 200 miles apart. That Jerry can was good insurance. My wife and I actually drove to the Arctic Circle in my Gen1, it was an adventure.

will