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An in-depth MPG analysis (Very Interesting)

889 Views 12 Replies 10 Participants Last post by  JettaTrek
I thought I'd share for the first time the latest results on my miles per gallon data collected on my 1997 Jetta Trek (2.0L).
Quick summary: I have meticuously tracked MPG since my car was new to its current 92,000 miles. To keep consistent, at each fillup, I ALWAYS fill the tank to full, and once the pump clicks off I stop - never topping off. While pumps will slightly vary when they stop, this is the only way to maintain consistency without always adding a specific gallon amount. Gaoline usage is then entered into an Excel spreadsheet.
OK, the data
Over the roughly 92k miles, I have an overall average of 30.20 MPG.
Mobil: Avg. 30.50 MPG (93 fillups)
Sunoco: Avg. 29.98 MPG (96 fillups)
Shell: Avg. 30.05 MPG (9 fillups)
Exxon: Avg. 30.33 MPG (42 fillups)
Others: Avg. 29.24 MPG (10 fillups)
Analysis - while it looks like Mobil is superior to all other in terms of MPG, the data is not what it seems. Sunoco was near my job when I got the car, and at that time it only averaged 28-29 MPG while it was breaking in. Mobil is where I go now most often and now I rarely get below 31 MPG per tank, even during current Sunoco fillups. The others category are generic stations and Gulf when I was desperate, which I do believe have inferior gas as the data shows.
Super (93 octane): 30.67 MPG (29 fillups)
Plus (89 octane): 30.09 MPG (124 fillups)
Reg (87 octane): 30.21 MPG (108 fillups)
Avg. MPG just during heavy A/C use: 31.59 MPG
The data used to show a definitive curve of about 0.5 MPG at each grade level, however, regular has surpassed plus. Although once again the data may be skewed as the car is breaking in. With gas prices being high. I went back to just regular last spring and have experienced great mileage in the 31-34 range each tank full since then. However, I would like to switch to all super for a while again to see the difference now. When my car hit 85k, I truely felt like it was finely broken in. The engine just seemed smoother, easier to rev, and actually it felt more powerful.
Some other notes, gas mileage goes down about 1-3 MPG in January and February during real cold periods (real cold periods here means never getting above 20 degrees). With the data graphed, there is a very visable trend of increased average MPG as the car gets older. The highest MPG I have recorded for a tankfull is 39.52 - with 2 bikes on the roof rack. This was attained during a complete highway trip on 93 octane gas, and I believe a strong tailwind.
Finally, if you're interested in my driving specs, I drive a mixture of highway/city with a split of probably 60/40. I will see a very slight increase if I take it easy over a full tank, but even if I'm driving hard, foot to the floor acceleration at highway on-ramps, etc...I don't see any noticeable difference. As shown, air condition use does NOTHING to reduce my mileage, and in fact I get some of my best results with the A/C on!
Thats it - its a little long but I thought some of you would find it interesting.
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1 - 13 of 13 Posts
Re: An in-depth MPG analysis (JettaTrek)

thanks http://****************.com/smile/emthup.gif
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Re: An in-depth MPG analysis (VR6 Mk3)

Great Data! I'd love to know of the results when changing to a new fuel filter, plugs and wires. There should be a noticeable difference in MPG.
Re: An in-depth MPG analysis (VR6 Mk3)

yeah, thanks man, awesome information there, very interesting to see, makes you not care about running regular octane, with the AC on
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Re: An in-depth MPG analysis (igneousGOlF)

Thats pretty damn cool.... i should figure out my gas mileage. I travel about 20 miles per day going to work. I fill up about once a week.
Re: An in-depth MPG analysis (JettaTrek)

JettaTrek wrote:
Avg. MPG just during heavy A/C use: 31.59 MPG
As shown, air condition use does NOTHING to reduce my mileage, and in fact I get some of my best results with the A/C on![HR][/HR]​
Do you drive differently when you have the A/C on?
Re: An in-depth MPG analysis (dumbnewbie)

wow thats crazy...some very good information thanks http://****************.com/smile/emthup.gif
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Re: An in-depth MPG analysis (JettaTrek)

Was this for your own knowledge or was it for school?
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Re: An in-depth MPG analysis (YellowGolfBall)

That is quite the impressive track you have there. That is something I wouldn't have the patience to do, so http://****************.com/smile/emthup.gif for you !
Very interesting to see how A/C didn't greatly affect your mileage. As Goobery69 said, I wonder how a new filter, plugs and wires affects it. Anyways, keep up the good work. It's nice to see consumers actually testing things for themselves, rather than just taking the manufacturers word for it.
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Re: An in-depth MPG analysis (JettaTrek)

I love people like you JettaTrek, this may be a stupid question, but I was just wondering is the tank in a 2.0 12.5 or 14 gallons? Ive been getting only 300 out of a full tank since new. I drive a mix of hwy and city. 60/40 I guess.
Re: An in-depth MPG analysis (GAIO GTI)

I think its 14.5
Re: An in-depth MPG analysis (igneousGOlF)

Anyone do this with a VR6...what happens if you use regular gas? is it bad? I've been using 93
Re: An in-depth MPG analysis (JettaTrek)

I thought I'd add a few more comments...
First off, I actually started this at 3,800 miles, so I have about 90,000 miles of data. When I fill up I write my mileage on the receipt, however, I lost the pile of receipts from the first 3,800 miles before I got around to thinking of keeping a spreadsheet. Yeah, this whole thing seems pretty anal, but once I got rolling, it is addictive. Anyway, here are some more facts/specs.
I am running stock except for: K&N air filter, which I desperately need to clean since I haven't in 55k, and Bosch platinum +4 plugs (same 55k). Of course, my mileage is better than ever, so I'm interested to see any change once I clean/change these parts and possibly replace the ignition parts. I also been thinking about the fuel filter.
Also, I have run with Mobil 1 synthetic oil since 24k with a VW filter, and I've used all the grades (0w30, 5w30, 10w30), but I don't see any data to suggest one is better than the other. I do all my own oil changes.
I can get 400+ miles to the tank taking it down into the small red area.
I don't drive differently with the A/C on to my knowledge. The A/C data is based on about 10,000 total miles where I noted lots of A/C use, mostly in July/August.
The only real conclusive data is winter/summer affects. Looking at the graph of the data, it is easy to see summer and winter seasons by the plots above and below the trend line. Winter definitely takes away some MPG.
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