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Old 03-18-2009, 11:18 AM   #1 (permalink)
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Some graphs of temperature vs. MPG

I started trip logs for my drive to and from school, and I'm bored right now, so I made some graphs of the data. I record the date, distance traveled, EOC miles on that trip, MPG for the trip, and the temperature. The distance, EOC, and MPG are measured by my MPGuino, and the temperature I look up at Welcome to Weather Underground : Weather Underground.

It's obvious that temperature makes a pretty big difference in MPG, but I thought I would make some graphs of it anyway, it's pretty interesting how the MPG follows the temperature:

First, the MPG vs. Temp and EOC vs. Temp on a log scale axis for my trips to school:


You can see a pretty good correlation between MPG and temperature here, but it's better if I take the log of the temperature, and then graph it:


And the same thing for trips from school:


And with the log of the temperature...


The EOC figures can't really be directly related to the temperature, because my EOC practices are more determined by other people on the road. If there are people behind me on one of the roads I travel, I usually won't EOC as much, because there are no passing zones, and I feel bad making everyone else go 35 in a 55. I think it just worked out that on nicer days, there were fewer people behind me

It's only a small time frame, so the correlation isn't perfect, but I thought it was still interesting to see.

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Old 03-18-2009, 04:07 PM   #2 (permalink)
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The question is how much does engine warm up factor in?
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Old 03-18-2009, 04:27 PM   #3 (permalink)
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Well, for all the trips going to school, I start the car, and spend about 1 minute clearing off the windows, as there's been frost on them every day. For the trips from school, I start the car, and leave, as the windows have been clear every day.

Next year, I'll try to get a block heater, and compare the results. I'm sure that they will be much higher, as engine warmup is probably the main factor for poor mileage in the cold. There's not much point in getting a block heater now though, as winter here is pretty much over.

Once the engine is warmed up though, the coasting mileage is still worse at low temperatures than it is at high temperatures. Obviously, there are other factors, like wind, but on colder days, my mileage at 55MPH is definitely worse than it is on warmer days.
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Old 03-18-2009, 05:47 PM   #4 (permalink)
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Here is some of my collected data. Daily commutes for 2008 and 2009 so far. No AC in the summer.

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Old 03-18-2009, 06:53 PM   #5 (permalink)
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Cool, I was just about to ask for a plot of temperature versus mpg, rather than the two plotted against the date. The data are extremely noisy as I expected. McTimson, would you post a similar plot of your data?
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Old 03-18-2009, 06:57 PM   #6 (permalink)
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Also, Pale, is that a polynomial fit? I would expect roughly linear behaviour, with discontinuities at the temps where you change your warm-up sequence, your ECU changes to a winter regime, and where you turn on your A/C.
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Old 03-18-2009, 07:39 PM   #7 (permalink)
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Very cool data, guys!
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Old 03-18-2009, 08:29 PM   #8 (permalink)
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I'll see if I can get a scatter plot in a little bit. I don't think it will look as nice though, I don't have nearly as many data points.
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Old 03-18-2009, 09:12 PM   #9 (permalink)
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Alright, here's the MPG vs. temperature graph for my data:


It's not as linear as I would expect, but I think that with more data points, it would become smoother. Again, this is only from like 2 weeks worth of recording, so it's not perfect, but it shows the obvious relationship between temperature and MPG.

I also attached the excel file if anyone wants to play around with the graphs.
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Old 03-18-2009, 10:22 PM   #10 (permalink)
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There is a definite leveling off of any gains past about 80 degrees. I don't use AC, so that's not the reason. I'm guessing 80-90 is the optimum intake temperature for my car.

I have very little data at the cold end, as you can see, so that's somewhat suspect. Most of this winter's points were on the high end there, while last winter had the low points. I think early results skewed the data. That, or just unfamiliarity with winter driving for mileage.

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