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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old September 17th, 2013, 22:16   #31
Diesl
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Just in case anybody cares, the plots in post #3 do update automatically when I update my spreadsheet (plus, the NSA gets a text message from Google). The five tank average reached a new record, but should level off any day now...
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Old September 18th, 2013, 02:52   #32
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Quote:
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... plus, the NSA gets a text message from Google ...
It's very handy. If you have a hard-disk crash & lose all your files, or drop your phone into the sea, they will have taken a backup of everything for you.
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Old November 8th, 2013, 19:19   #33
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Default corrected tire pressure & updated graphs

I've been driving less lately, so the fuelups are further apart, and the average temperature drops pretty fast for the last two fuelups. I also checked tire pressure: it hadn't dropped much, from 40 psi to about 35 for the lowest tire.
The graphs in post 3 have updated themselves.
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Old November 9th, 2013, 14:43   #34
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Added a temperature versus date chart to post #3.

Temperature is the average of the daily highs and lows for a given tank. I try to average just for the days I have actually driven the car, give or take a day or two. I could use the daily averages from http://forecast.weather.gov/product....n=2&glossary=0, or maybe even better the daytime averages. Best would be to have the car measure and average the temperature when it is driven. That would be a nice project, preferably for somebody else...
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Old November 10th, 2013, 03:27   #35
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Fuel Economy: Best 59 USmpg, average 47 USmpg, and improving...
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Thanks for the updates.

Out of interest, what is your typical driving like in terms of trip length, city/highway and speed? Just thinking in terms of what your data shows, since presumably short trips and city driving will be more affected by longer warm up times at lower temperatures, whereas increased aero drag will be more of a factor for long highway drives.
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Old November 10th, 2013, 08:54   #36
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I think I posted it before, but I'm commuting a bit over 40 miles (US) one way, 2/3 of it highway with typical Chicago area cruising speeds of about 75 mph. The average speed for the whole commute is about 40 mph. Every few days add ten minutes of stop-and-go traffic...
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Old November 10th, 2013, 09:22   #37
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Quote:
Originally Posted by Diesl View Post
I think I posted it before, but I'm commuting a bit over 40 miles (US) one way, 2/3 of it highway with typical Chicago area cruising speeds of about 75 mph. The average speed for the whole commute is about 40 mph. Every few days add ten minutes of stop-and-go traffic...
Thanks. You probably posted it elsewhere but it's not in this thread. Guess the aerodynamic effect is the dominant one?

US miles are exactly the same distance as UK miles by the way, it's gallons that are different which makes mpg figures different.
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Old February 24th, 2014, 15:17   #38
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Post 5 updated with new data. Is Spring near?!
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Last edited by Diesl; February 28th, 2014 at 17:35. Reason: post 5, not 3
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Old February 28th, 2014, 17:35   #39
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Default More plots

New plots: MPG rise and fall plotted by season (in post 5).
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Old March 21st, 2014, 11:23   #40
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Default Deviations from linear temperature dependence

Spring/summer 2014 graph started. The rise this spring from 36 to 37 mpg (five tank average) started BEFORE the temperatures went up. Odd.
The top graph shows the data and the best fit (linear) trend line.

The second plot shows the deviations from this trend line, to see whether there is some pattern to the mpg deviations from the temperature-predicted curve.



Difference measured MPG - predicted MPG
(Measured five-tank average minus best fit trendline):
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Last edited by Diesl; March 21st, 2014 at 18:26. Reason: add trend line plus residuals
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Old March 24th, 2014, 06:53   #41
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I've noticed better fuel mileage when the fuel tank is less than 1/3. My gut guess is the fuel warms up quicker with less to recirculate. I noticed that on the same trip that once I top off the tank the mpg decrease. (Instant mpg reading from the ecu)
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Old March 24th, 2014, 08:21   #42
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Thanks for the graphs Diesl! I'm seeing even great spread for my cold winters, about 20%. 33mpg this cold winter compared to 38-40mpg last fall.
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Last edited by APT; March 24th, 2014 at 08:46.
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Old March 29th, 2014, 06:42   #43
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More fuel as the temp goes up. We purchase fuel in lots of 42k gallons a shot (home heating oil, ulsd and nrlm )and it is temperature compensated to 65*f and is amazing gross vs net gallons even when my guys off load to a 3000 gallon truck. With expansion and contraction. That is my opinion.
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Old March 29th, 2014, 14:34   #44
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I see about a 20% change when it's cold, having to scrap the frost off the windows or the snow off the car before I can get going (yes, the engine is idling to warm it up during this process), then the biggest change is on snowy days I end up stopping at every traffic light as the traffic backs up, only going 30-45 mph instead of 60-70 because of icy roads also costs mileage due to the lower gear and having the engine turn many more rev's for every mile driven.
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Old April 1st, 2014, 13:28   #45
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Quote:
Originally Posted by 03_01_TDI View Post
I've noticed better fuel mileage when the fuel tank is less than 1/3. My gut guess is the fuel warms up quicker with less to recirculate. I noticed that on the same trip that once I top off the tank the mpg decrease. (Instant mpg reading from the ecu)
Interesting I have never noticed this trend.


I will be interested to see what my MPG will do as the temp arms up. I averaged 40-41 MPG through a colder then normal winter in northern IL. I have been getting 45-46 MPG over the last few tanks, and high temps have only been 30-50deg. Yeasterday the temp was in the mid 60's and I got over 50MPG to and from work. I like the way this trend is heading!
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