Data tracked initially on a notebook and then later directly in Apple Numbers using a shortcut. Plotted using Apple Numbers.

Very consitent trend with peaks in ~July and valleys in ~January. For context, I live in the northeast US, so this is likely a combination of factors including variable road conditions, increased use of 4WD, and gas additives. My actual truck usage does not change appreciably over the course of a year.

Posted by RamblinEagle13

50 comments

  1. That’s very interesting, and confirms what my gut has been telling me about my vehicle in terms of seasonality coupled with long term mechanical efficiency decline.

  2. Great dataset! You’ve been tracking this every month since 2018? Bravo

  3. That’s interesting. Looks like your wife also saves spare napkins and stuffs them in the glovebox.

  4. Interesting. … Since this is DataIsBeautiful, I have to note that the x-axis isn’t quite beautiful. Would be more easily interpreted if the tick marks were at 12-month intervals.

  5. I recently learned about summer and winter blend gasoline. Assuming this is gas and not diesel, that may also contribute to the sinusoid. Great dataset!!

  6. This might be the first time I ever saw truly beautiful data on this sub

  11. You should try imposing a sinusoidal prior on the model with a 12 month period to see how well it fits.

    Y = A*sin(B + freq*x) + Cx + D (assuming I’ve not messed it up)

    Fix freq to whatever it needs to be for how the time series is represented, or perhaps make it a variable (I’d personally fit it).

  13. My grandparents logged mileage and gallons with each fill up on every car they drove. He sold used cars from his front yard and the little book with that info went with the car.

    I’d love to have seen him plot this out. He worked for Boeing back in the day and was prone to that kind of stuff.

    This is very interesting.

  14. Care to share the data? This would be a great dataset to use for teaching

  15. Simply colder temperatures resulting in the engine spending more time running cold contributes to the periodic trend as well.

  16. This is really cool, there’s some info here that I wish I had.

    What is the year make and model of vehicle? Could you mark when you changed oil? When you filled tire pressure? When you replaced tires? Tires have the biggest impact on fuel economy in a normally operating vehicle so I’d love to have more data points here. Did you switch brands of tires? Assuming they were replaced in the 7 years you had the vehicle. How many miles did you put on the vehicle in this time period.

    I am just wondering what other factors could be at play here.

  18. I love this. Thank you. I have a lot of people telling me my EV will lose range and efficiency over time but don’t believe me when I say that ICE do too. This is really beautiful data.

  19. Very similar to EVs, slow degradation over time with wild swings in efficiency between winter and summer.

  21. Actually, interesting data.
    I would add that apart from fuel, tires have a large impact on fuel economy, if you are not vigilant about maintaining tire pressures. Also, being in the NE if you switch from summer to winter tires or from normal to run flats.

  22. That’s interesting. Make and model? What maintenance have you done over the 7.5 years and when?

  23. So seasonally you see about a 25% drop in efficiency, and over 7 years have seen about a 5% drop. Interestingly this seams pretty close to what EVs see

  25. I’ve heard that gas stations switch to “winter gas” in mid September, which effects fuel efficiency. 

    This combined with color winter combustion temps, longer warm up times, and 4wd push the average down. 

  26. You ought to annotate the mileage with oil changes, just to see if there’s a meaningful impact.

  28. Nice dataset. Similarly, I tracked my fuel efficiency for ~8’ish years and had similar seasonal fluctuations. I picked up a consistent 6% efficiency switching to full synthetic oil and a K&N air filter, if any value to you. I should dig up that dataset…

    Now that most vehicles do a good job tracking for me I’ve become too lazy to do it manually!

  29. OP, how much weight have you gained since 2018? I may have a theory…

  30. Funny to see this as I do the exact same thing with all my cars (example below for a car that finally gave the ghost in 2024 – indeed tracked using a numbers spreadsheet). I simply record the mileage and added gas when I fill er up and the spreadsheet calculates the real mpg from those. I have not seen your kind of long term trend on my cars. They have mostly been consistent over the years. The seasonality is mostly due to the fuel mix changing in winter to cut down on air pollution I believe. Also days of long highway drives like on a road trip should give higher mpg spikes as ICE cars have higher mpg when driving at constant highway speeds as you don’t get the big losses from constant deceleration and acceleration that happen in city driving. One thing you can see in the graphs is some issues that needed repair like this car’s catalytic converter going bad in january 2016. The gas mileage went down precipitously before the car showed other signs. I had a bad sensor in 2018 explaining that outlier. so keeping track of this is useful to catch some issues before they become bigger.

    https://preview.redd.it/o8ji7q95t5ag1.png?width=2128&format=png&auto=webp&s=ffa636fb76c273d758ff83ffca65e6e2181a6f90

  31. The sparse data points during 2020-2021 is mildly interesting.

  32. ive been watching my car slowly decline over the last few years as well and was curious if it was normal. really interesting to see what seems like a similar rate. (~24.8 -> 23.6 over the last year and a half or so with it running an average i havent reset in just as long)

  33. Do you have the vehicle mileage data? I would like to see the relationship between odometer and fuel mileage.

    On new vehicles fuel mileage typically improves as odometer miles accumulate. (According to various sources and both of my new cars I’ve owned.)

  34. A 10% efficency decline over 10 years doesn’t seem to bad. Actually, if that estimate is correct, it seems pretty damn good.

    I wonder if it’s to do with increased friction in all the bearings. Or decreased sealing if the various engine seals?

  35. Cool!

    It’s not truly sinusoidal, of course, just cyclical. That would imply a physical phenomenon originating from the engine itself, which of course simply isn’t the case- the programming is not changing.

    What IS changing is the temperature, and most vehicles, ICE or EV, have a sweet spot/valley, not too hot, not too cold, and summer tends to be closer to the right spot than winter. So the wave goes up and down based on ambient temperature, not anything you said- those variables would instead account for the day to day differences in measurement, outside of standard error. The wave is 100% an outside influence on the system and is in my opinion clearly temperature based.

    Nice data!

  37. You might want to employ that in conjunction with a drawn reciprocation dingle arm to reduce sinusoidal repleneration.

  38. I see that the vehicle was not used as much in the spring months of 2020

  39. I’d be curious to see if maintenance at all affects it, because 2023 seems to be your lowest fuel economy year afterward it seems to increase decently. Maybe new tires?

  40. Ticks on the x-axis should correspond to years’ starts, that way it’s easier to pick up the period of the oscillation (since we see it). Lower MPG in winters – maybe it’s a sign of warming the truck?

  41. can be caused by the degrade of variable components like the pcv system of your engine, leaks in vacuum hoses, carbon buildup in valves etc, it’d be interesting to fix possible minor issues and see if this helps in a course of some time

  43. Kinda reminds me of those graphing tick timer things they use for watch repairs.

  44. Try replacing your spark plugs, getting the fuel injectors cleaned, and ensuring that your air intake filter is clean.

  45. Nice graphing, I appreciate this! Winter fuel blends are the biggest reducer, I believe. I use the FillUp app for the same data. The graphs aren’t quite as refined as your graded average over time, but it gives a good look, too

  46. I am in a similar trend although my peaks and valleys are not as drastic (+2/-1).

    Started at 21mpg back in ’15, getting ~19mpg in ’25 after 182k miles. Air filter every 20k, spark plugs every 40k, need to do a walnut blast of the combustion chamber.

    It would be interesting to go back and mark when I changed my tires. I went from factory 17″ HT to 18″ AT to 18″ HT to 20″ HT which with higher weight, could contribute to my degradation.

  49. Clearly shows the seasonal decrease in mileage from cold weather

  50. I wish the dates on the x-axis were more uniform so it would be easier to visualize what the peaks and troughs correlate to! Otherwise, beautiful data set!

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