Is using A/C more fuel efficient than opening a window?

  • Thread starter Thread starter Ivan Seeking
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AI Thread Summary
The discussion centers around various car-related myths and facts, particularly about tire maintenance and fuel efficiency. It mentions the belief that tire air should be changed periodically and warns against using fix-a-flat due to potential explosion risks during tire servicing. A debate arises over whether it's more fuel-efficient to drive with windows open or to use air conditioning, with insights suggesting that closed windows with A/C are better for highway speeds, while open windows are preferable in city driving. Additionally, the conversation touches on urban legends, such as moss growing only on the north side of trees and the historical figure of Thomas Crapper related to toilet design. Overall, the thread highlights the blend of automotive knowledge and common misconceptions.
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MIH was asking some questions about cars, which reminded me of the claim that the air in car tires should be changed periodically...because it gets stale.

Also, I was once told that I should never use fix-a-flat in the car tires or they will explode when serviced. The flat fixer allegedly uses a combustible gas that explodes due to sparks caused by the tire machine used at shops.

Moss only grows on the north side of trees.

If you are being chased by a bear, run downhill. Since their hind legs are longer than the front ones, when bears try to run downhill they tumble.

The toilet was invented by Crapper.
Actually, he was the engineer who designed the London sewer system.

...or maybe not
Thomas Crapper: Myth & Reality
http://www.theplumber.com/crapper.html
 
Physics news on Phys.org
The Rubix cube is solvable.
 
We only use 10% of our brains.
Well, this one is probably true with people who believe it.
 
If you step over a sleeping person, they could dye.
 
Claim: Some people spell dye as die.
Status: True! :biggrin:

Here's a good one. Claim: It is more fuel efficient to drive a car with the windows open rather than running the a/c. The opposite claim is also made. It turns out that [having just seen this discussed with a transportation expert] due to the turbulance and increased air resistance caused by open windows, closed windows with the a/c on is more efficient for driving at highway speeds, and for city driving it is more economical to open the windows and turn the a/c off.
 
My favourite urban myth is the one about the creatures spotted walking around Tokyo.

They made a documentary about it:

 
Last edited by a moderator:
Ivan Seeking said:
Claim: Some people spell dye as die.
Status: True! :biggrin:

Here's a good one. Claim: It is more fuel efficient to drive a car with the windows open rather than running the a/c. The opposite claim is also made. It turns out that [having just seen this discussed with a transportation expert] due to the turbulance and increased air resistance caused by open windows, closed windows with the a/c on is more efficient for driving at highway speeds, and for city driving it is more economical to open the windows and turn the a/c off.

Mythbusters did a episode on this. The fact that they could not test (can't remember why) over 45mph sort of voided their conclusion of no difference.

This last summer the AC in my car went out. I noticed a marked improvement in my gas mileage. I did not expect any change but it improved by about 3mpg. This was with short drives and around town. I did not do much freeway driving. Fortunately I had just replaced my driver side master window switch just a few weeks before the AC went out. Not being able to open windows was a pain with AC, I cannot imagine the misery had the AC went out AND I could not open windows.
 
Sir Joseph William Bazalgette designed the London sewage system.
 
"Moss only grows on the north side of trees."

This may be an urban legend if you take the word "only" too literally, but moss does grow preferentially on the north side of trees, at least in the northern hemisphere. Moss prefers damp, shady areas which are more likely to be found where the sun rarely hits. Of course there is nothing stopping it from growing on the south side of a tree, and the word "only" is too strong.
 
  • #10
How come moss growing is an urban legend, it sounds more like a country side legend.
 
  • #11
Borek said:
How come moss growing is an urban legend, it sounds more like a country side legend.

I don't know about the rest of you, but I was led astray by Lassie, on this claim. NEVER trust a crackpot collie.
 
  • #12
Integral said:
I did not expect any change but it improved by about 3mpg. This was with short drives and around town. I did not do much freeway driving. Fortunately I had just replaced my driver side master window switch just a few weeks before the AC went out. Not being able to open windows was a pain with AC, I cannot imagine the misery had the AC went out AND I could not open windows.

I'm not sure why Mythbusters had such a hard time testing this. It took me about 3 minutes. My track car (also a fun daily driven when called upon) has a piggyback computer for re-tuning and realtime data logging.

At 70mph, my data logger showed an injector pulse width of ~15% at full fuel rail pressure with the A/C off and cruise control on. Just switching on A/C causes an increase to ~16% or 17% to maintain the same speed. That's not a trivial difference. I noticed no change with my windows open, actually.

Here's a myth: driving 55mph saves gas.

I get my best mileage at about 80mph... although I would never know since I've never gone that fast on public roads.
 
  • #13
For me it isn't a question of fuel consumption so far as A/C goes.

It's more about what happens when you turn the A/C on versus what happens when you open a window.

Or, gentle ice cold breeze versus mildly cool gust of wind. Not to mention how difficult communication with passengers becomes with the window open.
 

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