Finding Average Temperature for a Tank

Discussion in 'Fuel Economy' started by HCHCIN, Jan 3, 2007.


    HCHCIN Well-Known Member

    Hi all--

    I logged the first tank of my new HCHII this morning (16 days between fill-ups, sweet) and while doing so found the blank for average temperature. Not knowing how to really figure that besides guessing (I'm sure some out there keep detailed logs, but I can't remember to do that), I went to my favorite weather website, Weather Underground, to see what I could find.

    Turns out there's a nifty little tool there that lets you put in custom dates and it will report the weather averages (including max, min, and mean for highs, lows, and daily mean) and precipitation for your city. Here's how:

    1) Go to, enter your ZIP code, and hit enter.
    2) When your city comes up, scroll down a little to the "History and Almanac" box.
    3) Enter the beginning date of your tank in the drop-downs there and click Go.
    4) The history for that date should appear. Below the date entry boxes, click "Custom."
    5) Enter the end date of your tank and click Go. (The beginning date should be retained.)
    6) There it is -- the weather almanac and history for the entire length of your tank.

    I used the Mean Temperature Average, which for my city and tank was 43 degrees F. If you don't drive much at night, I suppose you could use Average Max Temp, but that might require a little correction.

    I'll admit, it's a long way to go just to be a little more precise (I had initially guessed 40), but I'm sure there are some eggheads (like me) on this site that will like this. --RN
  2. tbaleno

    tbaleno Well-Known Member

    That is a great resource. Thanks for pointing it out. I've been pretty much doing guess work based on what my car told me the temp was each day.
  3. tarabell

    tarabell Well-Known Member

    I love this site too. I knew it had the almanac feature but didn't know you could get the average temp over a range of dates. I've just been using the average temp on the day I fill my tank.
  4. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi HCHCIN:

    ___Excellent find!

    ___Good Luck

  5. Mr. Kite

    Mr. Kite Well-Known Member

    Thanks. I was just wondering if there was a tool like that as I was entering tanks yesterday. At some point, I will go back and add average temps to all of my tanks.

    Nice find!!!
  6. efusco

    efusco He who posts articles

    Another thank you for the great find. I always just guess at the avg. temp for a tank when posting at GreenHybrid, now I can do it w/ a bit more confidence.

    HCHCIN Well-Known Member

    Hi all--

    You're all very welcome -- I didn't think this little web app would prove so popular! Glad to be of service. I find WUnderground to be the most comprehensive weather data website around. Glad I could introduce it to the masses... --RN
  8. Fredness

    Fredness HyperMilin' on E85

    I've been using the "weekly average mean" temperature (mean daily temperatures averaged over the week).
  9. pumaman

    pumaman Well-Known Member

    Weather Underground is my default weather page, but I didn't think of using the function you described. Thanks, I'll try it.
  10. diamondlarry

    diamondlarry Super MPG Man/god :D

    Thanks for the info about that site! I see that you can also find stats for wind and, if I'm looking at it right, I can tell which direction it was coming from too. Cool site.:cool:
  11. Bruce

    Bruce cheapskate

    One other tip that can make things easier...if you enter an end date before your start date (e.g. the previous year) and hit "Go", both date fields will be reset to your start date.

    This can be helpful if you're doing a bunch of tanks at once, working back in time, because it transfers your start date to your end date.
  12. Ernie Rogers

    Ernie Rogers Member

    Okay, I'll ask the dumb question--

    Why do you want to know the temperature?
  13. pumaman

    pumaman Well-Known Member

    Because the outside temperature greatly affects your gas mileage. You get worse mileage the colder it is.
  14. Ernie Rogers

    Ernie Rogers Member

    Okay, let's take that as an impirical fact. Why do you suppose that is?

    1) Rolling resistance is greater at low temperature?

    2) Air density increases?

    3) Cold intake air lowers combustion temperature?

    4) Energy density is lower in winter fuel? (True for diesel, at least, probably also for gasoline.)

    5) Shocks and springs are stiffer?

    What do you think? How much variation is there with temperature?


    1) Cold fuel is more dense

    2) No air conditioning

  15. HemiSync

    HemiSync Well-Known Member

  16. gershon

    gershon Well-Known Member

    The title of this thread seems to imply there is an optimum temperature to drive at. I'm thinking it's at warmer temperatures, but I don't know. Does it really make a lot of difference if you have synthetic oil and fuel injection?

    Gershon (I'm new at this.)
  17. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    You are correct -- there is an optimum temperature. Keeping track of the average temperature with your tank data will help you find it. :)
  18. pumaman

    pumaman Well-Known Member

    Regardless of what else you do, your FE will be worse in the winter, assuming you don't live in San Diego or Key West.

    This is because your engine is not at it's optimum efficiency until it warms up. When the ambient temperature is colder, it takes longer for the engine to warm up.

    Check the Mileage Logs of some of the folks who live in the northern states. I live in Missouri, and I went from around 41 mpg last summer to around 36 mpg this past winter. Now I'm back up to the 40s.

    As next winter approaches, you will see desperate hypermilers begin talking about grill blocks and engine heaters.
  19. pdw

    pdw Well-Known Member

    True, it's Easier to attain a peak/optimum vehicle operating temperature in southern Florida's hot environment. But once it is warm, an engine faced with Northern windchills still begins to shed the unecessary heat as it does in a heatwave.

    We pay for that cooling just like we pay for the AC-cooling. If we are talking about moderating tips like the grill or the plug-in .... those are just the top of the iceberg (so to speak) on what is possible to preserve/keep that kind of energy cost low when the sourroundings are frigid.

    I'm almost afraid to list the means I've employed to make it though the winter.
  20. alvaro84

    alvaro84 Homura-chan's selfishness

    I'm thinking of covering a part of the radiator at winter to warm the engine faster. Now the mornings/nights are in the 10-15C range and it doesn't seem to measurably hurt my FE, but last time temperature went close to 0C my FE dropped drastically: at that time I did 3-3.3L/100km (71-78mpgUS) by somewhat careful, conservative driving (light right wrist, using the highest possible gear, keeping speed limits, keeping as steady speed as I could, trying to avoid unnecessary accelerating and braking), but around freezepoint I couldn't do anything better than 3.5L, and even had a 3.9L/100km (60mpgUS) tank (it had a 70km city ride at -6C with a 2 stops - the 'season closing' ride on 31st of December :D)...
    I'm curious what next winter has for me.
    I'll keep an eye on tyre pressure (~sidewall max, don't want to go higher on 2 wheels, already higher than BMW's recommendations), but I think I'll give up on FASing down our street and the next few ones, I'm afraid I'd reach the freeway with a cold engine. I'll also have a bit higher load on the battery, my heated gloves eat up more 2 amps (got them this spring).

    edit. on the original topic: I usually just guess. I ride both early mornings and afternoons, virtually every tank.
    Last edited: Sep 22, 2009

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