How much time or distance does the MFD numerical MPG display account for? I have only reset my MPG display once in the 13,000 mile life of my car, and that was done probably 9,000 or so miles ago. I have noticed that sometimes over the course of a hundred miles or so, the MPG numerical display changes by a couple MPG. I thought that the MPG display was active from the last time I reset it, but if that was the case, a 100 mile trip shouldn't be able to move the MPG this much. I'm not sure I explained that very well... Which leads me to my original question -- anyone know how many miles the MPG display uses when showing its calculation? (Seems like it must be ~1000 miles or miles since last reset). Thanks, Mike
:huh: I think it's from the last reset...... mine has steadily been dropping since Oct & the colder temps.... (will admit to being too lazy to did for the truth.......)
The MFD displays cumulative mpg until it loses power or is manually reset. Being an accountant I just had to run some numbers. Assume your MFD is counting the last 9000 miles since your reset. At 9000 miles your display indicates 50mpg. You burned 180 gallons of gas. Now 100 miles later your MFD reports 48mpg. For this to happen you needed to burn 9.5833 gallons over that 100 miles for an average of 10.43482mpg. With all due respect, either you have someone stealing gas out of your tank, a hole in your bladder, a failing computer, or you really didn't mean to post that you lost 2 mpg. Suppose you meant you lost .2 mpg--going from 50 to 48.8 mpg. You would burn 6.4754 gallons in 100 miles for 15.44306 mpg. What do your manual calculations show? Here's my advice: When you fill up at the gas station, set the nozzle to the slowest position. Reset the MFD. Record your odometer reading. Next time you buy gas calculate your mpg. It should be within 2mpg of the MFD. If you meant to say that your calculated mpg is 2mpg lower than your MFD then I would have said that is normal. How far do you go on a tank of gas and how many pips do you show when you refuel? If you can provide better numbers I'll run them for you. My '75 LeMans with a 350cid V8 got 15mpg. I don't believe a Prius is even capable of getting 15mpg (unless it's short trips in the Arctic?). Keep us posted.
Thanks for the verification on my original understanding that it calculates based on last reset (or power loss). That was my original understanding. I probably overstated the "lost a couple MPG". It is probably more like losing a few tenths. Which still puzzled me. I tend to drive the car fairly consistently (I think!) between long commutes and local stop/go, so I was surprised to see a 100 mile trip affect average MPG so much. Say I went from an avg 48mpg over 9000 miles to an avg 47.7 mpg over an additional 100 miles, that would say my last 100 mile trip was running at about 30.3 mpg. Given my thought that I was driving the car relatively consistently, I would be surprised at the 30.3 mpg trip. I don't keep any manual data. And I can't be completely certain I didn't pull power over the past 9000 miles -- sometimes I muck around with the car and forget when I did it or if I pulled power...imagine that. My gut and some in-the-head calculations simply told me that the avg mpg was varying "too much" based on my assumptions that it averaged since last reset (or power removal). But, certainly, I will pay more attention to the magnitude of change on average mpg going forward. Thanks for the thoughts. Of course, since I plan to add another lumbar support soon, I'll be resetting the MFD since I disconnect power when I touch anything electrical in the car. Guess that'll be a good opportunity to see how the average number floats around...or at least write a note in my glovebox when I did it! Mike
Mike, I'm going to share a "real world" experience and you can bet I have the documentation to back it up. This also demonstrates why I hate the "guess gauge" and distrust the MFD. On Jan. 10 I had 8742 miles on the car and a lifetime 49.5mpg. (176.520 gallons) Over these last 2 weeks it has gotten freezing cold. Tonight on my 35 mile drive home from the office the "guess gauge" went from 2 pips to 1 flashing. The MFD said I went 390 miles on the tank at 52.9mpg. Being "cautious" (others no doubt will use a different word) I went out after dinner and filled up instead of trying to get one more trip from the tank. I now have 9134 miles on the car and I pumped 8.537 gallons to automatic shut off. So I calculate 392 miles at 45.9mpg. I reset my MFD after every fill up but usually I forget at the station so the difference in miles is understandable (and I believe insignificant). Through yesterday I would have said the MFD is within 2mpg of my calculations. Tonight I am rather annoyed that the difference is 7mpg--at best a 13% variance. This one tank dropped my lifetime mpg .1mpg to 49.4mpg. Do I really have another 3 gallons of gas in the bladder? How much farther would I have been able to go? Over the 3 mile drive home the MFD says I'm getting 66+ mpg at 36F. Do you think I believe it or can maintain it? My point is: Don't trust the instruments. If one were paranoid one could believe that Toyota sets them to calculate high to give ownwers a false sense of economy. There will be individual swings, high and low. (It happens in my Intrigue too.) Consistant techniques should produce consistant results over time. Ignore the fluctuations. Keep an eye on the trends. Right now I believe you don't have a problem, just didn't remember the numbers accurately.
Jim, you'll like the way we were taught to trust aircraft fuel gauges: you only believe them when they say "E."
Just an FYI.. On my 2007, when I fill up on gas, my MFD MPG display resets automatically. A nice feature.
<div class='quotetop'>QUOTE(toad @ Jan 25 2007, 04:52 PM) [snapback]380888[/snapback]</div> The MPG does or just the miles driven display? I know my 2006 resets the miles driven, but the MPG does not reset to 0 (on mine).
I'm pretty sure it resets the MPG. I don't remember what the display shows, but I know that before a fill up at around 450 miles, the MPG will barely change no matter the driving conditions. However, just after a fill up, the MPG will change by as much as 10 MPG depending on the driving conditions.
Agreed, I don't believe I have a problem...nor did I when I originally posted, actually. I was merely confused, as usual. I would tend to agree, yes, that Toyota has at least a vested interest in smearing any calcs to the high side of MPG. I wonder if the car secretly stores lifetime MPG anywhere, regardless of resetting the MFD? The lifetime MPG is all I really 'care' about with regards to milesage, and I use even that term loosely. Mike <div class='quotetop'>QUOTE(JimN @ Jan 23 2007, 06:07 PM) [snapback]379818[/snapback]</div>
