Why 99.9 MPG more than 5 minutes?

[2009Prius]

Just noticed this after getting home.



The last leg of the commute was local roads between 25 and 45 MPH. I am sure the ICE was on some of the time. There were no long stops. I don't understand how it got more than 5 minutes of 99.9 MPG.

[NYPrius1]

Were you going down hill?? They battery was sure kicking in.

[2009Prius]

Originally Posted by NYPrius1

Were you going down hill?? ...

There are some gentle up and down hills, but most of the route is pretty flat. Again I am sure the ICE was on at least some of the time.

[Matt Herring]

Originally Posted by 2009Prius

There are some gentle up and down hills, but most of the route is pretty flat. Again I am sure the ICE was on at least some of the time.

99.9 mpg is just the max the MFD displays for mpg. In EV mode my SGII typically reads 3500-4000 mpg while I'm in EV. In neutral coast my SGII reads 120-200 mpg until I get back into the ICE. So, 2 bars of 100 mpg on the MFD over 10 minutes is entirely possible...great job!

[a priori]

The ICE could have been on for a large portion of the time. The 5-minute bars are averages across each 5-minute period.

Don't be fooled or confused by the 99.9 reading. The readout shows only 00.0 to 99.9. Anytime the mileage reaches or exceeds 99.9 MPG the readout registers 99.9.

Let's take a quick look at how some of this could happen. I'll make some assumptions that may never happen in reality, but still serve to illustrate a point. We'll set you up to run a loop that covers one mile in five minutes. Each minute you cover the exact same distance (1,056 feet). Because you go up and down and either push on or let up on the accelerator, the ICE will turn on and off.

First time around: Let's say you have a machine that registers mileage each minute, and it tells you you've had steady MPGs for each minute at 74.3, 34.6, 98.2, 22.9 and 121.6. If you had the MFD screen give these readings, you could easily see the first four numbers but not the fifth, because it would register as 99.9. If you were steadily covering the same ground in each of those five numbers for one minute each, the 5-minute bar would show at about 70 MPGs.

If you had the same first four numbers for the next four minutes, but the final minute was at 275.1, the next 5-minute bar would show 99.9, instead of the actual 101. If on the next try you had a the same numbers for the first four minutes, but the fifth and final minute was when you were moving but the ICE was on for only the first couple of seconds, you could have had something like 1,235 MPG for that minute. The true 5-minute average would be 293, but the 5-minute bar would show 99.9.

Hope this helps!

[nooaah]

Yup, 99.9 is the max it will display, but you were doing better than that (clearly). For the last 10 minutes of my commute, I'm able to do battery to regen to battery without the ICE ever coming on. Even after I've driven 200 miles it still can raise my total MPG by over 1.

[donee]

Hi 09Prius,

Traffic pattern probably was accidentally in a Pulse and Glide, with the glides on some long down hills, and the pulses on short uphills and you hit the green lights. My drives to and from work each day, this time of year (50's to 80's F) show at least one period of 100 plus mpg. A good drive home will have up to 3 of them.

[CharlesJ]

Originally Posted by Matt Herring

99.9 mpg is just the max the MFD displays for mpg. In EV mode my SGII typically reads 3500-4000 mpg while I'm in EV. In neutral coast my SGII reads 120-200 mpg until I get back into the ICE. So, 2 bars of 100 mpg on the MFD over 10 minutes is entirely possible...great job!

So then, does the car computer computes MPG with that 99.9 as max to calculate MPG or does it use the actual what you read on the scan gauge, 3500, etc as well? I have been wondering about that.

[Trevor]

My bars typically look like that when I'm on my way home from a road trip. take the Verrazano bridge from Brooklyn into Staten Island, I get a really long downhill to the toll booth which tops off the battery, then it's all local streets, so if get all the lights then I get a pair of 99.9 bars at the end.

[2009Prius]

Originally Posted by CharlesJ

So then, does the car computer computes MPG with that 99.9 as max to calculate MPG or does it use the actual what you read on the scan gauge, 3500, etc as well? I have been wondering about that.

I bet the computer uses the actual fuel consumption, not the artificial display limit.