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MPG: Summer and A/C

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  #1  
Old 06-20-2018, 07:54 AM
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MPG: Summer and A/C

As soon as temperatures get into the 40s, my mileage increases dramatically. Now that it's summer, I really appreciate air conditioning. Not only is the car cooler, but it is also quieter.

People have been arguing about MPG and A/C since that luxury became available. I have never been able to determine a gas mileage difference between driving with and without air conditioning. I take the same routes several times during the week, and my average mileage per trip is always different. Turning on the A/C doesn't make a difference I can document.

Speed makes a huge difference, but I can't see any difference at all when using air conditioning. If I take the Interstate on a thirty-mile trip, I'll average about 44 MPG, but if I take the back roads, I can average 50 MPG or better. I see no difference using or not using A/C, so I'm not going to suffer in the summer heat for a theoretical MPG difference.

.
 
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Old 06-20-2018, 08:21 AM
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Agreed. I might see a maybe 1 MPG or so difference but it's not huge when factoring all the other variables on my daily commute. I just filled up yesterday and got 42.9 MPG, that's using A/C and non-econ. Econ and A/C just feels really unresponsive so I avoid it. I've done it in the past and gets about 1 MPG better, but it's miserable to drive.

Still beats the 17 MPG my 4Runner gets so I'm not complaining too much
 
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Old 06-20-2018, 08:31 AM
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I was wondering the same thing, so I tried a little experiment to introduce A/C as the only variable in MPG calculation, to see what effect it might have in real time.

If you engage cruise control while you're on relatively flat terrain, watch the MPG gauge as you turn the A/C on and off. Mine drops by 3-4 blips with the A/C on.
 
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Old 06-20-2018, 08:31 AM
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Originally Posted by 2Rismo2 View Post
Agreed. I might see a maybe 1 MPG or so difference but it's not huge when factoring all the other variables on my daily commute. I just filled up yesterday and got 42.9 MPG, that's using A/C and non-econ. Econ and A/C just feels really unresponsive so I avoid it. I've done it in the past and gets about 1 MPG better, but it's miserable to drive.

Still beats the 17 MPG my 4Runner gets so I'm not complaining too much
Every time a pickup or SUV blasts past me, I'm thankful that I'm driving a 40+ MPG Fit.
 
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Old 06-20-2018, 08:36 AM
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its too hot without a/c. i dont care for a 1-2mpg even 5mpg difference. a/c stays on.
 
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Old 06-20-2018, 09:00 AM
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Originally Posted by kenchan View Post
its too hot without a/c. i dont care for a 1-2mpg even 5mpg difference. a/c stays on.
I have a "thing" plugged into my OBD II port and it transmits all sorts of engine information to my Garmin GPS. Stuck in traffic in hot weather, I can see if engine temperature gets too high. If it does, I'll shut off the A/C, open the windows, and turn on the heat. That brings the temp right down.
 
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Old 06-20-2018, 09:06 AM
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the ecoRoute thingie? those things work real well, i had one in my old hobby car with a garmin too.

did dat thing provide oil temp or just the coolant temp? i forget.. really need to see the oil temp.
 
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Old 06-20-2018, 09:15 AM
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Originally Posted by kenchan View Post
the ecoRoute thingie?
Yes, that's it. I have to remember to unplug it when I'm having the car inspected annually.
 
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Old 06-20-2018, 03:42 PM
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my scangauge2 has a reading for gallons per hour. when I turn on the ac, my idle GPH reading goes from like 0.16 to 0.27 or something like that. can provided pics and better numbers if you care



TL;DR = its a tiny diff, just use the AC (esp on the highway)




side note:
If I recall, Mythbusters discovered that .... at low speeds, windows down is fine. at highway speeds, window down makes mpg worse .... or something like that.
AC vs Windows | MythBusters | Discovery
 
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  #10  
Old 06-20-2018, 03:44 PM
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Originally Posted by kenchan View Post
its too hot without a/c. i dont care for a 1-2mpg even 5mpg difference. a/c stays on.
Where's my "Like" button? Tampa Bay here; A/C is a must. I've used the heat twice in 4 years.
 
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Old 06-20-2018, 07:09 PM
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The people who don't see a difference, I don't suppose your default vent setting is windshield defog?

... because the AC is always on in that setting.

Personally I certainly do see a difference with and without AC, but at highway speed having the window open is just as bad, so assuming you don't like to boil I would just turn it on and ... if you really care about mpg ... slow down by 5mph which gets you, rough rule of thumb, 1mpg.
 
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Old 06-20-2018, 10:58 PM
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I have noticed that my MPG has been going down since summertime started. But I'm also one of those people that keeps the a/c on full blast most the time so that is to be expected.
 
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Old 06-21-2018, 10:44 PM
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Summer gas may be different and give lower mileage.
 
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Old 06-22-2018, 01:53 PM
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Over the 92k miles I've had my 2015 Fit, most of them on a regular commute route driven repeatedly in similar conditions (so I'm comparing like with like), I'd guess that having the a/c on costs around 1 to 2 MPG.

Two other factors that make a significant difference are whether the air intake is set to recirculate or suck in from outside (recirculate saves around 0.5 to 1 MPG in freeway cruising, I would guess) and the temperature of the outside air. Once that goes into the 90s (of Fahrenheit) and above, MPG takes a hit. We've just had a very hot week for June (afternoon temperatures of 110-115), and my commuting MPG dropped from low 40s to high 30s.
 
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Old 06-22-2018, 04:20 PM
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Originally Posted by Brain Champagne View Post
Summer gas may be different and give lower mileage.
really? thought they only have winterized or oxygenated gas for winter cause people like to idle their cars with remote start and all. burns easier with less pollution or something but also eats mpg.. so i heard.
 
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Old 06-22-2018, 05:02 PM
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I've noticed about a 2 mpg difference, but.....not enough to not run the AC …. I sweat enough in a 12 hour shift, am absolutely running the AC when I want to. And, fwiw, I always notice my mpg improves when they switch to "summer gas" …..so in the late spring/early fall (pre and post AC needs), I get really great mileage just tooling around town....stop and go surface streets, no hwys, steep hills and curves. AC puts a hit on it, but that's OK....I have such bad seasonal allergies that I rarely drive with the windows open anyway
 
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Old 06-22-2018, 05:27 PM
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Originally Posted by Brain Champagne View Post
Summer gas may be different and give lower mileage.

Good guess, but it's just the opposite.
 
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Old 06-22-2018, 07:36 PM
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Winter gas is formulated to be more volatile so it vaporizes more easily in cold temperatures to help start your car. This added volatility is removed in summer gas because the gas would lose too much in the way of fumes and vapors in the warm temperatures adding to local pollution levels. And yes, summer gas gives slightly better gas mileage.
 
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Old 06-25-2018, 05:02 PM
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I really don't see much difference in mileage when running the A/C. At least not compared to other factors that seem to have a bigger influence (rain, headwinds, winter gas, average speed).

Certainly not enough for me to worry about.
 
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Old 06-25-2018, 05:06 PM
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Originally Posted by woof View Post
Winter gas is formulated to be more volatile so it vaporizes more easily in cold temperatures to help start your car. This added volatility is removed in summer gas because the gas would lose too much in the way of fumes and vapors in the warm temperatures adding to local pollution levels. And yes, summer gas gives slightly better gas mileage.
Not only that, but the more volatile blends can "boil" in the fuel lines, causing vapor lock and stalling in hot weather.
 
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