Estimated versus actual mpg

The HSI screen doesn't show gallons used. You are thinking of the EV/HV ratio screen, which doesn't round off the gallons used. It instead truncates. It'll say 8 gallons used when I'll have put 8.75 gallons in the car. The truncation is very frustrating.

On the HSI screen, it will show an estimated running MPG. This number is based on the total miles driven, whether it's HV miles or EV miles. This is based on the last time you reset the screen. There are two screens, Trip A and Trip B. I use Trip A for the current tank and Trip B for a lifetime average. You toggle between them with the Trip button on the steering wheel.

If you want to know what your HV-only miles are for a particular tank, you need to have reset one of the EV/HV ratio screens (again there are 2 screens, 1 & 2, just like Trip A & B on the HSI screen) prior to filling the current tank. Divide the number of HV miles by the number of gallons you pumped and you'll get the gas-only MPG. I'm averaging between 45 MPG and 51 MPG for HV-only. When I add in the EV miles I do, I'm averaging between 55 and 65 MPG. My Fuelly page has notes for each fillup that includes the EV/HV values for each tank.

I have found that the Cons number reported by the HSI screen is a little optimistic. It's usually off by about 4% to 5%. Sometimes it's only been off by about 1% or 2%, but other times it's been off by nearly 10%. I try to be consistent with my fillups, but it's not always the same pump or even the same gas station, so there's a fair amount of variation. But if I average it over several or more tanks, the error rate is pretty consistent around 4%. According to my lifetime trip meter, it's claiming 61. According to fulley.com and 15 fillups, it's averaging 58.5. Which is about 4%. I can live with that error margin. My GenII 2005 tended to be optimistic by about 8% to 10%.

 

Unfortunately, that does not work. HV miles include blended miles, where both gas and electricity is used, so this method does not completely take out the contribution of electric power.

 

Need I point out that the Prius has always used a blend of gas and electricity? The PiP just has more electricity to play with.

Snarkniness aside, I get your point. The super-enhanced blended mode does muddy the water and makes it hard to determine your HV-only miles and equivalent HV-only gas milleage. However, I don't think it muddies the water so much that you can't make a decent guess at what the HV-only gas mileage is.

 

but it is free electricity outside of that recieved by plugging in, yes?

 

There is no such thing as free electricity (OK, those with solar panels can smirk). In blended mode, you are running up HV miles since the ICE is running, but really also using the battery. And in EV mode, you may be using energy regenerated from a climb powered by the ICE. Thus, I think the HV/EV ratios are pretty meaningless statistics. What counts is how much gasoline you burn plus how many kwh you pull from the wall.

 

this is what i'm saying. it would be nice to know actual mpg's and mpkwh's, but, apparently they are too intermixed to determine accurately.

 

Others will know the details, but my experience is that warm-up uses small amounts of gas (unless the engine was turned on by sharp acceleration). The PIP will use battery power when possible in order to warm the engine at limited revs.

 

Well, after owning the PiP for 33 days I finally went to the service station and filled er up. Notice I did not say "I finally had to fill er up". I did not - I still had 4 PiP bars left. However, tomorrow I head off for the first road trip @ 450 miles round trip and i wanted to see what she would do in all hybrid mode (minus the 12 miles from initial charge). I had 901 miles on my initial tank of gas. The computer said I had gotten 163 miles per gallon and I put 5.75 gallons into the tank. The actual calculation was 157 miles per gallon. So the computer was 6 miles high. Not too bad! Even better is the 157 miles per gallon! And frankly who's to say that the computer was wrong. I did not put the initial tank of gas in, the dealer did. Even if I had done it who's to say that all the gas pumps are set the same?? Either way +/- 6 mpg on 157 is pretty accurate. Speaking of accurate is the fact that I was down 6 PiP Bars and the car took 5.75 gallons of gas! Assuming each PiP bar is a gallon of gas this is pretty much what I should have put in - cool.

Rob

 

Mine is about spot on. Run these numbers.....



820.2/91= 9.01 gallons......heres the fill up:



90.03 MPG calculated. 91 MPG indicated.