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Old 01-12-2010, 06:05 PM   #1
steven765
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Member#: 105920
Join Date: Jan 2006
Location: Somewhere in the Northeast
Vehicle:
2006 Baja 5 Speed

Default MPG differential at 4 years

So I now have 4 years of data on my baja.
I log every receipt, miles driven, cost and grade fuel. I'm going to start tracking average speed per tank thanks to the scanguage, but i digress.
Anyway so with that every year I add to the table the differential on MPG over the previous year. yada yada results

06 ave mpg 25.03
07 ave mpg 24.44
08 ave mpg 23.36
09 ave mpg 22.46

for a differential of -0.59, -1.08 and -0.9 respectively off the first year

and an average standard deviation of 1.75 for the years individually or 2.06 in total

I could run the linear regression for a pretty chart later, but it will just tell me what I can see: that I'm trending downward at about 1MPG/year .
Regretfully I wished I had ave speed/tank to factor that in.

For reference this is over 372 tanks of gas, 4550.4 gallons of gas or 109k miles. At the prices paid that's $12,567 paid out for gas!

-1Mpg/year is rather sad. I'm about the replace the oxygen sensors hopefully that restores it a bit.

Next up I need to calculate the average MPG by brand of gas.

Yes I'm bored, but this is me procrastinating from doing research
..back to work now argh
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Old 01-13-2010, 11:29 AM   #2
kev m
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2010 Impreza 2.5 Wgn
2011 Nissan Juke

Default

One possible datapoint to consider - Fuel

Does your area use

1. Seasonal gasoline?

and/or

2. E10?

I ask because the months of availability of winterized/oxygenaed gas will likely have an effect on those numbers (as will seasonal average temperatures and number of miles in winter temps vs. summer temps).

Also, if your area changed to E10 gas year round anytime AFTER 06, that would also have an appreciable effect on your numbers.

Personally I don't log the gas receipts, but do spot check mileage at every single fill-up and I notice trends seasonally and with fuel types (not only on the Baja, but on all our vehicles, it can be even more pronounced on motorcycles - ours typically gain or lose 10 mpg without or with E-10 respectively).

That said - with mixed driving conditions and E10 I've pretty much seen 22 mpg from day one. With more highway and/or non E-10 I've seen as high as 26 mpg.
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Old 01-13-2010, 11:49 AM   #3
pagris
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Join Date: Sep 2006
Location: Western Maryland
Vehicle:
06 Baja Sport
Atlantic Blue Pearl

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I am thinking that average speed per tank might reveal a lot for you in this analysis, though it strikes me that it would be problematic to determine - perhaps activate a timer every time you start/stop the engine for the duration of every fill-up. Living in the Hampton area, I am guessing you might have to deal with traffic congestion at times (?)

As Kev M noted, I notice a significant decrease in my mileage in the winter months - I understand it is to be expected, it just seems a little more pronounced in the Baja than with other vehicles I have or did have, like roughly a 10-15 % decrease during daily commuting.

The other consideration is tires - I have seen considerable changes in mpg in some of my vehicles when I have purchased new tires that differed from the previous ones.

109 K in 4 years! Wow! My 06, purchased in 9/06, just turned 25K!
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Old 01-13-2010, 04:10 PM   #4
steven765
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Agreed the speed would help a lot. I noticed about a 4mpg drop with the stupid e10 gas, that happened just soon after I bought the car. I've not seen non e10 gas in NY, VA, or NH now I still wonder if the extra gas you burn because of the e10 negates the lower emissions.
Only one tire change so far, I wore those re92's down to slicks in va hehe. Replaced them is re960's I didn't see much of a change caused by them I looked.
I averaged jan-dev with the correlating stdev so that obviates seasonal causes in this case. Miles are pretty consistent month to month ~2-4k.

*tear* 25k in 4 years; I could only dream. I was driving to dc on a project taking the $ instead of flying, then i got smart then started taking rentals. Now my reserve site is 4 hours away and we don't get paid to travel as reserve so it's on me. The rentals would cost more than I get paid for a weekend's work If it's not one thing it's another.
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Old 01-13-2010, 04:40 PM   #5
kev m
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2011 Nissan Juke

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I dunno - 2-4k miles month to month is a pretty big swing - if the swings lined up seasonally one year but not another you would have some problems with the data.

Actually though, you should be able to tally the seasonal swings by your datalogging of each fill-up yes?
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Old 01-14-2010, 09:59 AM   #6
kev m
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2010 Impreza 2.5 Wgn
2011 Nissan Juke

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Got the new Impreza 2.5i up to 30 mpg this morning on a run over to NJ - though that was only for a moment, though the whole drive before that it was easy to maintain 27-28 mpg (even on a bunch of back roads, but with light traffic).

Not bad for "break-in" - obviously the Impreza benefits from better aerodynamics and I would assume lower weight - might be a difference in gearing too, I should check that.
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Old 01-14-2010, 06:07 PM   #7
steven765
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2006 Baja 5 Speed

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The first summer I once saw 33Mpg on a ny-dc run, but that was 06, i think it was after that summer the e10 became widespread.
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Old 01-15-2010, 10:12 AM   #8
bheinen74
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its due to ethanol.
more added in the fuel now.
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