Influence of window opening vs. A/C use on fuel economy
It has become popular lately to claim that turning on A/C uses less fuel than opening windows. On a recent round trip to Kansas I used my handy Scan Gauge to check milage under different operating conditions. (What else is there to do driving across Missouri and Kansas?) I checked the calculated fuel economy over approximate ten mile segments on each tank of fuel. I used the cruise control and the calibrated Scan Gauge mph measurements. Usually I could go the whole ten miles without touching the gas or brake. I tried to be as consistent as possible. For open windows, I started out rolling them all the way down but after a couple segments of that, I decided that no one could stand the tornado effect for long distances so I tried various partial open positions which improved ventilation without being punishing. Generally this was the rears open 4 inches and the fronts either closed or open 3 inches. The vehicle, unfortunately, was not typical for most drivers: 1998 Odyssey 4 cylinder with a Thule car-top cargo box. Newer A/C systems and less drag-challenged vehicles may yield different results, but here goes... Test 1 8/31/06 76 mph I35 Southbound Hilly 22.8 mpg overall (measured) A/C Windows # Segments Ave. MPG Relative MPG Off Closed 4 19.83 100 Off Full Open 2 19.45 98 Off Part Open 2 18.90 95 On Closed 4 18.24 92 Test 2 9/4/06 75 mph I35 Northbound Hilly 19.7 mpg overall (measured) A/C Windows # Segments Ave. MPG Relative MPG Off Closed 5 21.62 100 Off Part Open 3 21.27 98 On Closed 1 20.90 97 Test 3 9/5/06 75 mph I35 Northbound Hilly 23.4 mpg overall (measured) A/C Windows # Segments Ave. MPG Relative MPG Off Closed 3 20.43 100 Off Part Open 2 20.65 101 On Closed 3 19.27 94 Test 4 9/5/06 73 mph I55 Northbound Flat 21.6 mpg overall (measured) A/C Windows # Segments Ave. MPG Relative MPG Off Closed 6 22.22 100 Off Part Open 5 21.68 98 On Closed 5 20.82 94 Overall, weighted by number of segments relative to windows up, A/C off, fuel efficiency was: Windows open 98% A/C on 94% In this test, turning on the A/C cost three times as much fuel as opening the windows. There was no indication that it made any difference whether the windows were wide open, rears down 4 inches or front and rear both down 3 - 4 inches, but there was limited testing of this, and the effect was small in any event. As noted before the vehicle may not be typical, but these were the results. One further point of interest; shortly after I started one segment I came upon a speed reduced work zone. I didn't use the segment in the above calculations but I noted that average speed was 63 mph and average fuel consumption was 26.4 mpg. It appears that the difference between going 60 and going 75 was about 4 mpg. |
Re: Influence of window opening vs. A/C use on fuel economy
"Gordon McGrew" <gRmEcMgOrVeEw@mindspring.com> wrote in message
news:ml3uf21mpn3tgt45va1s5v7tch8u4un5p2@4ax.com... > Overall, weighted by number of segments relative to windows up, A/C > off, fuel efficiency was: > > Windows open 98% > A/C on 94% > > In this test, turning on the A/C cost three times as much fuel as > opening the windows. There was no indication that it made any > difference whether the windows were wide open, rears down 4 inches or > front and rear both down 3 - 4 inches, but there was limited testing > of this, and the effect was small in any event. > > As noted before the vehicle may not be typical, but these were the > results. One further point of interest; shortly after I started one > segment I came upon a speed reduced work zone. I didn't use the > segment in the above calculations but I noted that average speed was > 63 mph and average fuel consumption was 26.4 mpg. It appears that the > difference between going 60 and going 75 was about 4 mpg. > The Mythbusters did a controlled experiment, with the result being windows down = a lot better mileage. http://cartalk.com/board/showthreade...60&page=6&vc=1 The link above leads to CarTalk's forums. The post notes that their computer models said the mileage should be practically the same. The real experiment showed otherwise. -- R Flowers |
Re: Influence of window opening vs. A/C use on fuel economy
"Gordon McGrew" <gRmEcMgOrVeEw@mindspring.com> wrote in message
news:ml3uf21mpn3tgt45va1s5v7tch8u4un5p2@4ax.com... > Overall, weighted by number of segments relative to windows up, A/C > off, fuel efficiency was: > > Windows open 98% > A/C on 94% > > In this test, turning on the A/C cost three times as much fuel as > opening the windows. There was no indication that it made any > difference whether the windows were wide open, rears down 4 inches or > front and rear both down 3 - 4 inches, but there was limited testing > of this, and the effect was small in any event. > > As noted before the vehicle may not be typical, but these were the > results. One further point of interest; shortly after I started one > segment I came upon a speed reduced work zone. I didn't use the > segment in the above calculations but I noted that average speed was > 63 mph and average fuel consumption was 26.4 mpg. It appears that the > difference between going 60 and going 75 was about 4 mpg. > The Mythbusters did a controlled experiment, with the result being windows down = a lot better mileage. http://cartalk.com/board/showthreade...60&page=6&vc=1 The link above leads to CarTalk's forums. The post notes that their computer models said the mileage should be practically the same. The real experiment showed otherwise. -- R Flowers |
Re: Influence of window opening vs. A/C use on fuel economy
"Gordon McGrew" <gRmEcMgOrVeEw@mindspring.com> wrote in message
news:ml3uf21mpn3tgt45va1s5v7tch8u4un5p2@4ax.com... > Overall, weighted by number of segments relative to windows up, A/C > off, fuel efficiency was: > > Windows open 98% > A/C on 94% > > In this test, turning on the A/C cost three times as much fuel as > opening the windows. There was no indication that it made any > difference whether the windows were wide open, rears down 4 inches or > front and rear both down 3 - 4 inches, but there was limited testing > of this, and the effect was small in any event. > > As noted before the vehicle may not be typical, but these were the > results. One further point of interest; shortly after I started one > segment I came upon a speed reduced work zone. I didn't use the > segment in the above calculations but I noted that average speed was > 63 mph and average fuel consumption was 26.4 mpg. It appears that the > difference between going 60 and going 75 was about 4 mpg. > The Mythbusters did a controlled experiment, with the result being windows down = a lot better mileage. http://cartalk.com/board/showthreade...60&page=6&vc=1 The link above leads to CarTalk's forums. The post notes that their computer models said the mileage should be practically the same. The real experiment showed otherwise. -- R Flowers |
Re: Influence of window opening vs. A/C use on fuel economy
Windows down messes up my wife's hair. A few miles per gallon is cheap for my peace of mind. Just my .02 Spdloader |
Re: Influence of window opening vs. A/C use on fuel economy
Windows down messes up my wife's hair. A few miles per gallon is cheap for my peace of mind. Just my .02 Spdloader |
Re: Influence of window opening vs. A/C use on fuel economy
Windows down messes up my wife's hair. A few miles per gallon is cheap for my peace of mind. Just my .02 Spdloader |
Re: Influence of window opening vs. A/C use on fuel economy
On Wed, 06 Sep 2006 19:41:47 GMT, gRmEcMgOrVeEw@mindspring.com (Gordon
McGrew) wrote: > > >It has become popular lately to claim that turning on A/C uses less >fuel than opening windows. On a recent round trip to Kansas I used my >handy Scan Gauge to check milage under different operating conditions. >(What else is there to do driving across Missouri and Kansas?) > (snip) Interesting information, but when it's 105 when I leave work, I'll use my AC and just pay the difference. Better than being covered in sweat and having all the dirt stuck to me. Average Hi temp for August in my area=100 degrees. Thanks, but I'll just keep the windows up!!! |
Re: Influence of window opening vs. A/C use on fuel economy
On Wed, 06 Sep 2006 19:41:47 GMT, gRmEcMgOrVeEw@mindspring.com (Gordon
McGrew) wrote: > > >It has become popular lately to claim that turning on A/C uses less >fuel than opening windows. On a recent round trip to Kansas I used my >handy Scan Gauge to check milage under different operating conditions. >(What else is there to do driving across Missouri and Kansas?) > (snip) Interesting information, but when it's 105 when I leave work, I'll use my AC and just pay the difference. Better than being covered in sweat and having all the dirt stuck to me. Average Hi temp for August in my area=100 degrees. Thanks, but I'll just keep the windows up!!! |
Re: Influence of window opening vs. A/C use on fuel economy
On Wed, 06 Sep 2006 19:41:47 GMT, gRmEcMgOrVeEw@mindspring.com (Gordon
McGrew) wrote: > > >It has become popular lately to claim that turning on A/C uses less >fuel than opening windows. On a recent round trip to Kansas I used my >handy Scan Gauge to check milage under different operating conditions. >(What else is there to do driving across Missouri and Kansas?) > (snip) Interesting information, but when it's 105 when I leave work, I'll use my AC and just pay the difference. Better than being covered in sweat and having all the dirt stuck to me. Average Hi temp for August in my area=100 degrees. Thanks, but I'll just keep the windows up!!! |
Re: Influence of window opening vs. A/C use on fuel economy
On Wed, 06 Sep 2006 19:41:47 GMT, gRmEcMgOrVeEw@mindspring.com (Gordon
McGrew) wrote: >It has become popular lately to claim that turning on A/C uses less >fuel than opening windows. On a recent round trip to Kansas I used my >handy Scan Gauge to check milage under different operating conditions. >(What else is there to do driving across Missouri and Kansas?) .... You sir are a gentleman and a scholar. However, the numbers are small enough, say 2%, that on a $50 tank of gas we're talking $1.00. And you sure can't hear the radio with the windows open more than a crack at speed. I do guess the window numbers would be more significant for an Accord without the antlers and big slab sides, might get it up to, oh, who knows, 5%?!? But presumably the A/C numbers would be the same, which would validate the claim which your experiment did not, but would still be just about $1.00/tank in the other direction. OTOH, windows would impose less overhead at slow speeds, say in stop and go, ... oh, where will it end?! J. |
Re: Influence of window opening vs. A/C use on fuel economy
On Wed, 06 Sep 2006 19:41:47 GMT, gRmEcMgOrVeEw@mindspring.com (Gordon
McGrew) wrote: >It has become popular lately to claim that turning on A/C uses less >fuel than opening windows. On a recent round trip to Kansas I used my >handy Scan Gauge to check milage under different operating conditions. >(What else is there to do driving across Missouri and Kansas?) .... You sir are a gentleman and a scholar. However, the numbers are small enough, say 2%, that on a $50 tank of gas we're talking $1.00. And you sure can't hear the radio with the windows open more than a crack at speed. I do guess the window numbers would be more significant for an Accord without the antlers and big slab sides, might get it up to, oh, who knows, 5%?!? But presumably the A/C numbers would be the same, which would validate the claim which your experiment did not, but would still be just about $1.00/tank in the other direction. OTOH, windows would impose less overhead at slow speeds, say in stop and go, ... oh, where will it end?! J. |
Re: Influence of window opening vs. A/C use on fuel economy
On Wed, 06 Sep 2006 19:41:47 GMT, gRmEcMgOrVeEw@mindspring.com (Gordon
McGrew) wrote: >It has become popular lately to claim that turning on A/C uses less >fuel than opening windows. On a recent round trip to Kansas I used my >handy Scan Gauge to check milage under different operating conditions. >(What else is there to do driving across Missouri and Kansas?) .... You sir are a gentleman and a scholar. However, the numbers are small enough, say 2%, that on a $50 tank of gas we're talking $1.00. And you sure can't hear the radio with the windows open more than a crack at speed. I do guess the window numbers would be more significant for an Accord without the antlers and big slab sides, might get it up to, oh, who knows, 5%?!? But presumably the A/C numbers would be the same, which would validate the claim which your experiment did not, but would still be just about $1.00/tank in the other direction. OTOH, windows would impose less overhead at slow speeds, say in stop and go, ... oh, where will it end?! J. |
Re: Influence of window opening vs. A/C use on fuel economy
Great job. Please test next without the luggage on top and replace 4
cylinder with 6. "Gordon McGrew" <gRmEcMgOrVeEw@mindspring.com> wrote in message news:ml3uf21mpn3tgt45va1s5v7tch8u4un5p2@4ax.com... > > > It has become popular lately to claim that turning on A/C uses less > fuel than opening windows. On a recent round trip to Kansas I used my > handy Scan Gauge to check milage under different operating conditions. > (What else is there to do driving across Missouri and Kansas?) > > I checked the calculated fuel economy over approximate ten mile > segments on each tank of fuel. I used the cruise control and the > calibrated Scan Gauge mph measurements. Usually I could go the whole > ten miles without touching the gas or brake. I tried to be as > consistent as possible. > > For open windows, I started out rolling them all the way down but > after a couple segments of that, I decided that no one could stand the > tornado effect for long distances so I tried various partial open > positions which improved ventilation without being punishing. > Generally this was the rears open 4 inches and the fronts either > closed or open 3 inches. > > The vehicle, unfortunately, was not typical for most drivers: 1998 > Odyssey 4 cylinder with a Thule car-top cargo box. Newer A/C systems > and less drag-challenged vehicles may yield different results, but > here goes... > > > Test 1 8/31/06 76 mph I35 Southbound Hilly > 22.8 mpg overall (measured) > > A/C Windows # Segments Ave. MPG Relative MPG > Off Closed 4 19.83 100 > Off Full Open 2 19.45 98 > Off Part Open 2 18.90 95 > On Closed 4 18.24 92 > > > Test 2 9/4/06 75 mph I35 Northbound Hilly > 19.7 mpg overall (measured) > > A/C Windows # Segments Ave. MPG Relative MPG > Off Closed 5 21.62 100 > Off Part Open 3 21.27 98 > On Closed 1 20.90 97 > > > Test 3 9/5/06 75 mph I35 Northbound Hilly > 23.4 mpg overall (measured) > > A/C Windows # Segments Ave. MPG Relative MPG > Off Closed 3 20.43 100 > Off Part Open 2 20.65 101 > On Closed 3 19.27 94 > > > Test 4 9/5/06 73 mph I55 Northbound Flat > 21.6 mpg overall (measured) > > A/C Windows # Segments Ave. MPG Relative MPG > Off Closed 6 22.22 100 > Off Part Open 5 21.68 98 > On Closed 5 20.82 94 > > > Overall, weighted by number of segments relative to windows up, A/C > off, fuel efficiency was: > > Windows open 98% > A/C on 94% > > In this test, turning on the A/C cost three times as much fuel as > opening the windows. There was no indication that it made any > difference whether the windows were wide open, rears down 4 inches or > front and rear both down 3 - 4 inches, but there was limited testing > of this, and the effect was small in any event. > > As noted before the vehicle may not be typical, but these were the > results. One further point of interest; shortly after I started one > segment I came upon a speed reduced work zone. I didn't use the > segment in the above calculations but I noted that average speed was > 63 mph and average fuel consumption was 26.4 mpg. It appears that the > difference between going 60 and going 75 was about 4 mpg. > > > > > |
Re: Influence of window opening vs. A/C use on fuel economy
Great job. Please test next without the luggage on top and replace 4
cylinder with 6. "Gordon McGrew" <gRmEcMgOrVeEw@mindspring.com> wrote in message news:ml3uf21mpn3tgt45va1s5v7tch8u4un5p2@4ax.com... > > > It has become popular lately to claim that turning on A/C uses less > fuel than opening windows. On a recent round trip to Kansas I used my > handy Scan Gauge to check milage under different operating conditions. > (What else is there to do driving across Missouri and Kansas?) > > I checked the calculated fuel economy over approximate ten mile > segments on each tank of fuel. I used the cruise control and the > calibrated Scan Gauge mph measurements. Usually I could go the whole > ten miles without touching the gas or brake. I tried to be as > consistent as possible. > > For open windows, I started out rolling them all the way down but > after a couple segments of that, I decided that no one could stand the > tornado effect for long distances so I tried various partial open > positions which improved ventilation without being punishing. > Generally this was the rears open 4 inches and the fronts either > closed or open 3 inches. > > The vehicle, unfortunately, was not typical for most drivers: 1998 > Odyssey 4 cylinder with a Thule car-top cargo box. Newer A/C systems > and less drag-challenged vehicles may yield different results, but > here goes... > > > Test 1 8/31/06 76 mph I35 Southbound Hilly > 22.8 mpg overall (measured) > > A/C Windows # Segments Ave. MPG Relative MPG > Off Closed 4 19.83 100 > Off Full Open 2 19.45 98 > Off Part Open 2 18.90 95 > On Closed 4 18.24 92 > > > Test 2 9/4/06 75 mph I35 Northbound Hilly > 19.7 mpg overall (measured) > > A/C Windows # Segments Ave. MPG Relative MPG > Off Closed 5 21.62 100 > Off Part Open 3 21.27 98 > On Closed 1 20.90 97 > > > Test 3 9/5/06 75 mph I35 Northbound Hilly > 23.4 mpg overall (measured) > > A/C Windows # Segments Ave. MPG Relative MPG > Off Closed 3 20.43 100 > Off Part Open 2 20.65 101 > On Closed 3 19.27 94 > > > Test 4 9/5/06 73 mph I55 Northbound Flat > 21.6 mpg overall (measured) > > A/C Windows # Segments Ave. MPG Relative MPG > Off Closed 6 22.22 100 > Off Part Open 5 21.68 98 > On Closed 5 20.82 94 > > > Overall, weighted by number of segments relative to windows up, A/C > off, fuel efficiency was: > > Windows open 98% > A/C on 94% > > In this test, turning on the A/C cost three times as much fuel as > opening the windows. There was no indication that it made any > difference whether the windows were wide open, rears down 4 inches or > front and rear both down 3 - 4 inches, but there was limited testing > of this, and the effect was small in any event. > > As noted before the vehicle may not be typical, but these were the > results. One further point of interest; shortly after I started one > segment I came upon a speed reduced work zone. I didn't use the > segment in the above calculations but I noted that average speed was > 63 mph and average fuel consumption was 26.4 mpg. It appears that the > difference between going 60 and going 75 was about 4 mpg. > > > > > |
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