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Getting Better Gas Mileage In Warm Weather? Here's Why Page 2

 
2,788 views Jul 31, 2012
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Fuel gauge

That, as you can imagine, helps improve rolling resistance, compared to the winter months when lower tire pressures result in more drag.

Warm air also affects oil viscosity too. Oil becomes thinner when it's warm, which is fairly academic once the engine is up to temperature, but important when the engine is cold and can spin with less friction--and of course, it takes less time for an engine to reach its ideal working temperature in warm weather.

Finally, some states sell different grades of gasoline in the winter than in the summer. In summer, gas has higher energy content, burns more efficiently, so more of that gas is used to move you down the road, improving mileage.


So there you have it--want to know why your car is getting better gas mileage now than it was six or seven months ago? Plenty of reasons! Just enjoy it while it lasts...

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Comments (25)

  1. fb_1001015277 avatar John Briggs Posted: 7/31/2012 10:23am PDT

    I have always wanted to know the answer to this question. Unfortunately the author supplies no data or links to support his prose.

    The initial claim of air density seems totally off the mark. The engine management system will adjust to put out the needed power so efficiency should not change...however...

    When it is hot out side, the air is less dense and easier to push out of the way, and therefore the car is more efficient.

    So perhaps the author has the right parameter, but the wrong explanation. Does anyone have any real data?

    And the idea that the heater draws more power than A/C seems to neglect the fact that heat is "free" for ICE cars.
     
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  2. Anne-nl avatar Anne vdbom Posted: 7/31/2012 11:13am PDT

    Yup, missed that one too: aerodynamic drag is probably the biggest single factor.
     
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  3. fb_1559222512 avatar Xiaolong Li Posted: 7/31/2012 10:47am PDT

    huh?

    Some of MOST unscientific explaination ever... Terrible article.

    First of all, huge assumptions about the weather pattern in the winter vs. summer. In states such as FL and AZ, or most Southern states, it is actually rains more in the summer than winter. Maybe it is the case in England, but it certainly doesn't apply everywhere...

    2. Sure, hotter air is less dense. Less air equal to less fuel. But where is the proof that "air flow sensor" will detect a difference in air temperature adjusted flow rate? All cars are computer controlled that its fuel will be adjusted based on driver input and air intake. If the car lacks power, the driver might drives it slightly harder to compensate for the difference and increase fuel use.
     
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  4. Anne-nl avatar Anne vdbom Posted: 7/31/2012 11:25am PDT

    You observation that it rains more in summer than in winter is partly correct. This is also true for Western Europe, although the difference (measured in mm's) is small.

    What does make a difference is that rain in winter usually falls in short bursts and due to the higher temperatures, the road surface dries up quicker.

    In winter, the road can stay wet for days on end. Not because of more rain, but a lack of evaporation.
     
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  5. Anne-nl avatar Anne vdbom Posted: 7/31/2012 11:25am PDT

    Oops, I meant to say that the rain in summer falls in short bursts.
     
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  6. fb_1559222512 avatar Xiaolong Li Posted: 7/31/2012 10:52am PDT

    Continued,

    Accssories arguement are okay. Assuming that you have longer day lights during the summer over winter so people don't have to use headlights as much. That can impact your mpg. Heaters are essentially free for ICE cars (non-hybrid). The colder climate might require more electric defrosting and longer "warm up" (bad practice) time so drivers will burn more gas that way.

    Lower temperature will result in lower tire pressure (but any good owners will adjust that monthly). The oil argument is silly b/c it only impacts "start up" temperature. Once the engine is warmed up (fairly quickly), the temperature difference is miniscule. There are auto shops that switch different grade of oil between winter and summer.
     
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  7. fb_100003906173361 avatar Josef Mitterer Posted: 8/7/2012 12:27pm PDT

    oil temperature is usually not controled by a thermostat (like coolant water). so it is cooler in winter and has increased friction -> lower mpg -> close the radiator grill (at least alittle bit). or use oil with lower SAE nr.
    "warm up" without driving the vehicle is just for idiots. time the engine is running in cold and dangerous conditions is increased by this stupid manner. such people usually can not read or even calculate mpg;-)
     
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  8. fb_1559222512 avatar Xiaolong Li Posted: 7/31/2012 10:56am PDT

    Continued,

    as far as air resistance go, that is only a hwy assumption. If you drive slower, the difference are undectable.

    Mostly, all those differences can be easily masked by how heavy your foot is.

    Out of all the factors, the tire argument is valid if the owners don't check their pressure between season. The oil argument is ONLY valid if shops change the grade of oil between winter and summer. Most of the gas wasted in the winter are due to excessive unnecessary warm ups by the driver. Headlight and electric defroster contributes some, but they are all small "potato" in the large scheme of things...
     
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  9. fb_1001015277 avatar John Briggs Posted: 7/31/2012 11:36am PDT

    Thanks for the added input.

    The fact remains, I get significantly lower gas mileage in the winter than in the summer on both my ICE car (Corolla) and hybrid (Prius).

    I watch my tire pressure and don't do anything different in warm up (get in and drive). I am not sure what accounts for the difference, winter to summer.
     
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  10. fb_1559222512 avatar Xiaolong Li Posted: 7/31/2012 3:31pm PDT

    Well, I expect EV and Hybrid to get worse MPG b/c battery loses charges in colder temperature. Your Corolla probably gets worse MPG due to the cold start where the initial few miles, the engine and emission system will take longer to reach "efficient" states. The longer it takes, the less efficient it gets. That is probably the "main" contributor.
     
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  11. fb_100003906173361 avatar Josef Mitterer Posted: 8/7/2012 12:34pm PDT

    yep!
    cold start (like choke in old times)still happens even if you do not "idiot-warm up" the engine and start driving immediately.
    so what is the everage distance you drive with car, starting in cold engine conditions?
    if this distance is low this "choke" has high percentage and you see reduced mpg-
     
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  12. Anne-nl avatar Anne vdbom Posted: 7/31/2012 11:19am PDT

    Another factor for those using all weather tyres: warm tyres supposedly have lower rolling resistance.

    Plus hybrid behaviour. The Prius does a warmup cycle when you start it. It does this afaik for two reasons: 1 warm up the catalytic converter 2 warm up the interior. Only after this has occurred, will the full hybrid mode kick in. This makes the Prius extra sensitive to cold weather. You loose the hybrid advantage for the first few km.

    One trick I learned is to switch off the heater in winter during the second and third km. After the 3rd km, I can switch it on at the lowest setting (16 degrees C), without dropping out of hybrid mode.
     
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  13. fb_1001015277 avatar John Briggs Posted: 7/31/2012 12:37pm PDT

    The FOURTH post in this forum has an interesting graph. Clearly Air Temperature (and presumably density) is important.
    http://ecomodder.com/forum/showthread.php/outside-air-temperature-mpg-14440.html
     
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  14. fb_1559222512 avatar Xiaolong Li Posted: 7/31/2012 3:34pm PDT

    Well, it is commonly known that colder air is denser. Denser air will produce higher compression and more power...
     
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  15. fb_1001015277 avatar John Briggs Posted: 8/1/2012 7:09pm PDT

    Is it that, or the higher drag created by denser air.
     
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  16. fb_1559222512 avatar Xiaolong Li Posted: 8/3/2012 12:22am PDT

    Do you "gain" efficiency driving at higher elevation due to "thinner" air? Well, your engine lose efficiency faster than your car gain in less air resistance...
     
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  17. fb_1559222512 avatar Xiaolong Li Posted: 8/3/2012 12:23am PDT

    Maybe we should compare the MPG rating the same car in Denver vs. Florida and see if there are any difference in effiicency gain... :)
     
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  18. rickr avatar Rick Roberts Posted: 8/5/2012 2:24pm PDT

    you guys are picking nits. the fact is, the story is not based on any facts or valid science. It's based on the gut feelings of a moron.
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  19. john_v avatar John Voelcker Posted: 8/5/2012 2:27pm PDT

    @Rick Roberts: This is your friendly site moderator. Keep it polite, please. Criticize on the facts all you like, but no insulting authors or other commenters, OK?
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  20. fb_100003906173361 avatar Josef Mitterer Posted: 8/7/2012 12:42pm PDT

    yes but only if throttle is open completely.
     
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  21. kidmarc avatar kid marc Posted: 8/1/2012 11:09am PDT

    This has been fun... [giggle giggle]

    Peace
     
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  22. rlbatez avatar rob batez Posted: 8/3/2012 8:39pm PDT

    One important point overlooked here is that the fuel itself is warmed up considerably during the summer months and therefore the the fuel atomizes easier than when its cold - you can actually buy kits to prewarm the fuel using the engines coolant! although its more popular on diesels rather than gas engines but many claim a 5-10% mpg increase using this device.
     
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  23. fb_100003906173361 avatar Josef Mitterer Posted: 8/7/2012 12:40pm PDT

    well do serious racing teams use such "devices"????
    this is all compensated by ECU
     
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  24. gvii avatar Gary V Posted: 8/5/2012 7:50pm PDT

    Poorly written article. Not only does it spit in the face of the laws of thermodynamics, especially as they apply to IC engines, but it also shows an utter lack of under hood experience. The absolute absence of any supporting data outside of "personal experience" tells a great deal as well.
     
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  25. fb_100003906173361 avatar Josef Mitterer Posted: 8/7/2012 12:16pm PDT

    your statement "...and if there's less oxygen, the engine compensates by using less fuel...."
    is not correct! if the engine uses less air and less fuel it provides les power right? and thos is compensated by the driver. noone is aware abought the exact pedal position!

    tyre pressure. you are right. just check when it gets cold! mpg isthe same.

    winter tires: not correct. winter tires have much more tire profile. so the same tiresize has more diameter compared to the summer tire. more diameter means less rotations for the same distance. as trip is calculated by counting rotations you will see less miles on wintertires compared to the same track by summer tires...so you see less mpg. don´t belief in everything you see!
     
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