Computer vs. computed MPG

people who dont understand why people track both pump and computer dont realize that the more points of data you have, the more imformed you maybe.

i tracked both to see if any pumps gave me favorable mileage...didnt find any of those, but did detect a pump that was most likely shorting me.

 

Hmmm 25 mile error in 22000 plus miles. Hey that's about a .001 percent error. Very very serious.

 

oh ya... keeps me up nights!!

actually i've been kinda losing my touch. when i first got my Prius, the MFD was higher. then the pump slowly past it. my "heyday" was at between 13,440.8 miles and 14,022 miles where at some point in that tank, my MFD and my pump calculations MATCHED PERFECTLY!!@@!

but those were the days...been going downhill ever since

 

Happens all the time. Rounding error? Who you going to call?

 

I've never tracked this kind of thing before, but I started when there were only a few of us geeks on this forum (damn you John 1701A!!!) and we were curious about EVERYTHING having to with this car... and now that I've started... I...CAN'T...STOP!!!!!!! I'm serious....I don;t want the data and I've tried to stop, but I've been doing it since Nov 2003. What if I stop now and then in 3 months, wish I had it???

I think I need professional help!!!

 

Just turned over 15,000 miles on my '05, thought I would share my numbers:

distance driven since pickup: 15138
Refill gallons dispensed: 317.92
Calculated MPG: 47.6
Weighted average MPG per MFD: 49.1
Gallons consumed per MFD: 308.35

Average cost / gallon $2.35
Cost of gasoline purchased: $745.97
Savings over 15MPG Jeep: $1622

I suspect that the dealer had about 8 gallons in the car when I picked it up last summer, which accounts for 2-3 gallons difference, but can't explain the other 7 or so gallons.

Anecdotally, my calc vs MFD was closer in warmer temps. I was within the 2-3 gallon mark until temperatures turned cooler in the winter. Maybe the gas station pumps are less accurate in winter and claim that they dispense more than they actually do in colder temps?

 

I also have been keeping records on my new Prius...down to the trip (for tax purposes). So far, after three tanks, am averaging a little above 50mpg. I did, however, find a gas pump that was rather off. So, keeping this data does help.

 

The thing that drives me nuts is that I don't trust the manual calc because it's very hard to get reproducable results at the gas station. Variation in temps and pumps means that it's hard to know if you're replacing what you burned or not. On my last fillup I put 9.87 gal (US) into the tank and that's the most I've ever put in the thing. As a result, I've seen that the fuel gauge jibes with what others have reported. In the past the first blip used to go off at about 72 mi. This last tank it loitered until ~124 mi. As a result I'll probably go over 500 on a tank for the first time in 5k+ mi with the car. Dont' know why the tank suddenly took on more fuel but it really highlights the way that the bladder can play Old Harry with the manual calculations. <_<

I just go by the MFD since that's a (hopefully) consistent measurement that's independent of quirkly fuel pumps and fluxuating temperatures.

 

<div class='quotetop'>QUOTE(tripp @ Apr 10 2006, 01:24 PM) [snapback]237699[/snapback]</div>

That is why only long term calculations are accurate after a few gallons and a few thousand miles patterns begin to build up. I would say that a 3 or 4 tank running average is closer to how you are doing. Exceptions are wide swings in the weather and gasoline formula change season. Both cause jumps that are real. Averages over seasons give trends. If you make radical changes in route, driving style or distances for your day to day commute there will be major shifts. Addition of "mpg" aid such are radiator blockers, block heaters will cause shifts from one year to the next. Then there is the holy grail "plug in hybrid" that will give the old average a kick in the, well, posterior.

 

<div class='quotetop'>QUOTE(hdrygas @ Apr 10 2006, 08:37 PM) [snapback]237886[/snapback]</div>

very well said Henry and at least that will be a kick UP...with that in mind....

HURT ME HURT ME!!

 

<div class='quotetop'>QUOTE(FreshAirGuy @ Mar 13 2006, 12:27 PM) [snapback]224207[/snapback]</div>

I want to justify droping the big bucks for a new Prius when I could have been using my old SUV instead. My wife still looks at me like a naughty boy who just got a big toy. So, I want to be sure that when I tell her that the new Prius gets 52 MPG on my way to work instead of the 13 MPG of the old truck, I am right.
Does it make financial sense to buy the new Prius? Probably not on a dollar to dollar comparison, but it feels great to drive on rolling hills at 35 MPH and see the batteries recycling the energy spent climbing the hills.
I was in a bumper to bumper traffic yesterday going back home, and still got the 52 MPG :lol:
Yesterday, I was impresses by people getting around 100MPG on the "pulse and glide" technique. So, if there are people who want to increase their FE, there is plenty of room to play.
Cheers.

 

<div class='quotetop'>QUOTE(hdrygas @ Apr 10 2006, 09:37 PM) [snapback]237886[/snapback]</div>

Are you planning on doing that mod Henry? I hope to, if the Li-Ion batteries become a little more reasonable in price (not that I know what they actually cost now).

Dave M.