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Discussion Starter · #1 ·
This week I took a road trip on Interstate 80 across Nevada. The temps climbed into the 80s during the day. I tried to not use the A/C or open a window for as long as possible, but eventually it got too hot in the car and I had to do something.

In the Nevada desert there are many stretches of road that are long, straight and flat. I decided to do some tests on gas mileage using the instant mileage readout on the DIC. I tried rolling down various windows. Windows up with AC on. Sunroof open, etc.

Then I discovered something I have never experienced before. I had the sunroof popped up when I accidentally hit the button for the rear, passenger window, which opened it about an inch. Suddenly there was a strong vortex of air flowing throughout the entire car. It was like I turned on a massive fan in the back. The temps in the car dropped immediately, and there was very little noise. It even cooled my feet, which were getting hot from the heater core (terrible design flaw in my opinion).

In my tests, this combination of sunroof/rear window dropped the gas mileage about 2 MPG. The A/C seemed to drop the gas mileage about 4-5 MPG. This was measured by watching the instant mileage on the DIC, so it may not be very accurate.

Has anyone else discovered this interesting airflow with the sunroof and rear window?
 

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That vortex you spoke of works the same on many vehicles. Problem is the passenger (if you have one) gets little to no air (my experience). Roll up the passenger side, and roll down the driver side and the passenger has all the air, and you have next to none. Great way to save mpg's and stay cool with little noise if you are flying solo.
 

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I also noticed that having the sunroof popped up in the back and the rear windows down about an inch, there is a lot of airflow through the whole cabin.
I have been trying to find the best combination of passenger comfort and fuel mileage.
I read somewhere that having the back windows open around an inch, specifically in the Cruze, that the fuel mileage increases. I haven't confirmed this yet.
My current technique is to run the air conditioner when coasting or going downhill. I know it seems weird and extreme, but my commute is ALL hilly roads, my AC runs about 30% of the time. I keep the fan speed on 2-3 and turn the compressor on when my instant mpg are 99 mpg.



-Brad
 

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Did you try running the ac in recirclute mode when you were testing mpgs? I seem to get better mileage when using recirculate since it helps ac run more efficently cooling the air it alreasy cooled instead of hot fresh air from outside. I too did notice this vortex affect with the rear pass window and open sunroof. Btw I always keep the recirculate button light on hoping for mpgs but not sure if it does help.
 

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Discussion Starter · #5 ·
Did you try running the ac in recirclute mode when you were testing mpgs? I seem to get better mileage when using recirculate since it helps ac run more efficently cooling the air it alreasy cooled instead of hot fresh air from outside. I too did notice this vortex affect with the rear pass window and open sunroof. Btw I always keep the recirculate button light on hoping for mpgs but not sure if it does help.
I didn't even think about recirc mode. I will try that on my next drive. It seems like that would be very useful when driving like Brad does where you only use the AC downhill. That way you continue to recirc the cool air when the A/C is off. I will try that method next time as well.
 

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Small note: the Cruze automatically recirculates the air on coldest AC setting (even though the light is not lit up - you can hear the airflow change slightly and if you listen real closely, the damper motor move as well). Turn it up one notch above the coldest setting for outside air.
 

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I have weathertech visors on my front and rear windows, with them all cracked and inch I can stand up to around 85F without the AC(on the highway). I also get that vortex you speak of, as my drivers and passenger windows air is not coming in but being sucked out. I shut off my HVAC entirely most of the time.
 

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Yesterday I played around with this idea on my 110 mile commute home. I don't have a sunroof but opened the passenger window about 1-11/2 inches and did the same on drivers rear. If I reset the computer at the begining of the drive (all interstate, cruise set at 68mph) I get anywhere from a 47.5-49.5 average readout, with my best several being 50.2-50.5. Yesterday when i pulled off the interstate i was at 53.4 a number I had never seen before. This morning on the way here I kept the windows up (it was only 58 degrees out) and was at 49.2. I won't make the return trip until friday, but am curious to try it again and see what happens. My guess is that it was another factor, including computer error, but we will see. I'll be making the trip 1x per week now in the summer months and try it some more and report. If I find similar results I'll double check with actual gas fill-ups as a source for mileage.
 

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Small note: the Cruze automatically recirculates the air on coldest AC setting (even though the light is not lit up - you can hear the airflow change slightly and if you listen real closely, the damper motor move as well). Turn it up one notch above the coldest setting for outside air.
Which is a gripe I have with the car. It should not do that, or at least light the indicator when it does.
 

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I shut off my HVAC entirely most of the time.
Same here, but I do it mostly so it can't be smelly. I have found recirc mode does eliminate the smell though.

Also, shutting the power button off on the automatic system saves all the previous settings for next time. If I power the system down in my Excursion, it resets to factory default when I turn it back on. So the Cruze is easy to shut off and turn on. However, I usually make sure that A/C and AQS is off first because I don't trust that it won't continue to run with the power off based on how the system reacts.
 

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Discussion Starter · #12 ·
Yesterday I played around with this idea on my 110 mile commute home. I don't have a sunroof but opened the passenger window about 1-11/2 inches and did the same on drivers rear. If I reset the computer at the begining of the drive (all interstate, cruise set at 68mph) I get anywhere from a 47.5-49.5 average readout, with my best several being 50.2-50.5. Yesterday when i pulled off the interstate i was at 53.4 a number I had never seen before. This morning on the way here I kept the windows up (it was only 58 degrees out) and was at 49.2. I won't make the return trip until friday, but am curious to try it again and see what happens. My guess is that it was another factor, including computer error, but we will see. I'll be making the trip 1x per week now in the summer months and try it some more and report. If I find similar results I'll double check with actual gas fill-ups as a source for mileage.
That is very interesting. Keep us informed of the results. It would be interesting to see if this is true.
 
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