Toyota Tundra Best Fuel Economy – A/C or Windows Down

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An ongoing discussion it seems on virtually every automotive website has to do with whether you get better MPG with the A/C on or windows rolled down during the summer. Research finally has a definitive answer for full-size truck owners.

Toyota Tundra Best Fuel Economy

What is the better fuel economy strategy when it is hot – A/C or windows down? Research has finally answered this question.

The researchers at Oak Ridge Laboratory have looked at whether you get better MPG with the A/C on or windows rolled down. The colloquial wisdom has been that running the A/C taxes the engine and burns more fuel. While the window down argument is that you are essentially creating more wind resistance thus burning more fuel. Who is right? Both apparently.

The researchers tested a 2009 Toyota Corolla and Ford Explorer on a “Burke Porter 300-hp (224-kW) two-wheel-drive dynamometer” inside a laboratory that is “climate-controlled, and the testing was done at 95°F (35°C).” Originally, the idea was to do the testing on public roads, but likelihood of “too much variation from such factors as humidity, wind direction, and grade (and the resulting transmission shifting activity) over the period of time necessary to provide enough data.”

The findings reported on SAE.org have found that:

  1. At speeds below 75mph, rolling down the windows is more fuel efficient on both vehicles tested (a Corolla and a Ford Explorer)
  2. At speeds above 75mph, A/C was more fuel efficient on the Corolla, but was NOT more fuel efficient on the Explorer. The reason? The large cabin in the Explorer was hard to cool adequately.
Toyota Tundra Best Fuel Economy - Window Up or Down - Chart

Here is the research chart Oak Ridge Laboratories created explaining their findings.

The bottom line: Tundra owners should probably drive with their windows down all the time if they’re trying to save gas. Car owners, however, can drive with their windows up when they’re on the highway without fear of wasting gas.

What do you think? Do you agree with these findings?

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  1. Mickey says:

    I would think that driving with windows down would cause more drag. SInce the lab refuse to do it as a real scenario and did it in close doors I won’t agree with them. We drive in real surroundings not a lab. That’s all in part of trying to get best mpg’s when you can drive without having to change the speed or using cruise control. Real weather conditions plays alot into it. I am one who always likes to drive with all windows down. SUnroof and back glass only when it’s under 50 degrees down to 40 degrees. I like the feel of the air circulating. With the wife though it’s A/C period.

    • Tim Esterdahl says:

      I hear you Mickey. My beef though with windows down is that I live in the city. So, I either get loud music or exhaust fumes. When we visit family in the country though, I am windows down.

      -Tim

      • Mickey says:

        One thing I failed to mention. With back glass down you will have to vacuum the headliner. I did mine already 12x. It does get dirty from the junk in the air while you’re going down the road.

        • Tim Esterdahl says:

          Mickey,

          That is really good to know actually. I figured there had to be a downside to having the back window roll down. Not that this is a BIG downside, more of an annoyance.

          -Tim

  2. tonyspin says:

    When it is hot out I turn on the air. I don’t care how much it costs.

    • Tim Esterdahl says:

      Tonyspin,

      I’m with you, I don’t see why this is such a big deal to people. So what it costs a few dollars/cents more during the summer, I want to drive in comfort.

      -Tim

  3. mendonsy says:

    If you look at their chart closely it seems a bit strange.
    At 65 mph they used approximately 2.0 gals for 100 miles, a 50 mpg average!!
    I suspect the rest of their information is about as reliable as that chart.

  4. GoBIg says:

    There is another variable that seems to be missing. Older A/C units were either on or off. Most of the new ones offer a temp setting that would influence how hard the A/C has to work depending on the “cool” temp selected.

    I may have to put this question in the chicken and egg category as unsolved.

  5. art64 says:

    Yeah this laboratory setting is bs cause it’s not real world. Same as the bed cover. You put a truck in a wind tunnel where the wind goes only from front to back. In real world, the wind can go side ways, it can have gusts to so many mph, the moisture in the air can cause more drag, etc..and these will affect the results big time.

  6. mk says:

    I have driven enough in my lifetime mostly rural hwy. roads going 62 mph that I know for a fact that rolling down the windows saves more gas than running A/C. A/C sucks more gas and I only use it if over 88 degrees outside is all and humid.

    • JK says:

      MK, my experience differs. On a 2001 Chrysler Sebring, driven 162k miles mostly freeway… at 70mph, I would average 34mpg using the A/C, and 28mpg rolling down the windows… and the A/C was always more effective at cooling the car.

  7. mk says:

    JK,

    what did you expect, it is a Chrysler? Sorry, could not resist. Seriously, I have no idea why your vehicle differed that much which is pretty astonishing differences in mpg. At most I could see 1-2 mpg differences but that much is hard to fathom, but anything is possible I guess?

    I do know that air currents over say 70 mph greatly reduce co-efficiency and more drag. On my scooter or cycle 70 mph or more, on cycle anyways, the wind gusts are much more than say 55 mph. I once was on my scooter going 70 mph pretty much top speed for 250cc and about 30 mph winds NO windshield and the darn wind currents coming at me almost blew me off the scooter my jacket was all puffy and pushing me off the scooter pretty hard to hold onto handlebars.

  8. pete says:

    mmm yeah this dont make sense

    according to this the slower you drive the less feul you use per 100km. ??? as 5th gear is 80km/h min gear this makes little sense.
    Are they saying high revs in 4th gear uses less feul than low revs in 5th gear??

    defies logic im afraid.

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