Texas_Ranger
New member
I was just curious if anyone out there did a comparison of MPG with A/C on and then off. Some cars take a pretty big hit with the A/C on and others barely make a difference. Any insight would be great.
Does our A/C hurt our MPG?
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MaddoxPics
New member
Haven't seen any excessive drops. Definitely has some, but nothing I'd be concerned about.
MikeYQM
New member
I run an OBD monitor. At idle with A/C off I burn 1.3 liters per hour and with A/C off it’s about 2.3 or a bit more. Assuming that increase is relatively constant through the power band, at 100km/h I get 11.5 l/100km with it off or 12.5l/100km with it in.
1 litre = 0.264 Gal
11.5 l/100km = 20.45 mpg
12.5 l/100km = 18.8 mpg
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1 litre = 0.264 Gal
11.5 l/100km = 20.45 mpg
12.5 l/100km = 18.8 mpg
Sent from my iPhone using Tapatalk
Saker
Senior Member
MikeYQM's numbers look extreme to me, not saying they are incorrect.
If you drive with your windows down vs running A/C, wind resistance will more than likely reduce your mileage as much as windows up running A/C.
DISCLAIMER: just my opinion, no scientific data to back this up
If you drive with your windows down vs running A/C, wind resistance will more than likely reduce your mileage as much as windows up running A/C.
DISCLAIMER: just my opinion, no scientific data to back this up
rushrunner
New member
No, because you don't need A/C. Just roll the back window down.
MikeYQM
New member
I am confident the numbers at idle are accurate, that’s about it. Anything beyond that is extrapolated based on assumption and not much else. There are so many variables that accurately calculating the difference in mileage at cruising speed is pretty hard.
I don’t think ~ 2mpg is extreme, it’s only in the realm of 10% or so but I’m not an expert; I can only rely on my measurements and observations.
As for the windows, I believe windows open in the city and closed on the highway is most efficient.
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I don’t think ~ 2mpg is extreme, it’s only in the realm of 10% or so but I’m not an expert; I can only rely on my measurements and observations.
As for the windows, I believe windows open in the city and closed on the highway is most efficient.
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I have fuel economy data on my 2015 4Runner from both winter/summer here in Cali...where cranking the window down just won't cut it! :-D
I dare say there is barely 1mpg difference over time...mostly city driving though.
It's hard to compare WINTER/SUMMER ... since we tend to do longer trips in SUMMER.
Using a coarse data CUT, SUMMER = MAY to SEP (where AC is on almost all the time) and WINTER = OCT to APR (where AC is probably on a couple of times)
MPG SUMMER = 17.217
MPG WINTER = 15.967
DELTA = 1.25MPG
CONCLUSION
Can't separate WINTER/SUMMER gas impact compared to short/long trips or impact of AC but you can see last few tanks were long ass trips, dragging the average up!
I dare say there is barely 1mpg difference over time...mostly city driving though.
It's hard to compare WINTER/SUMMER ... since we tend to do longer trips in SUMMER.
Using a coarse data CUT, SUMMER = MAY to SEP (where AC is on almost all the time) and WINTER = OCT to APR (where AC is probably on a couple of times)
MPG SUMMER = 17.217
MPG WINTER = 15.967
DELTA = 1.25MPG
CONCLUSION
Can't separate WINTER/SUMMER gas impact compared to short/long trips or impact of AC but you can see last few tanks were long ass trips, dragging the average up!
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I have hardly ever turned mine off. I cannot even recall when I turned mine off, except when I was up north once in the winter for a trip.
You can see in my "what is your MPG" thread what my numbers have been. If there is an impact (and there is of course), it is not significant.
I get 21.something highway, 18.something city, it has been pretty constant the four years and 37,000+ miles I have owned it. AC on probably 99.99999% of the time (live in Miami).
You can see in my "what is your MPG" thread what my numbers have been. If there is an impact (and there is of course), it is not significant.
I get 21.something highway, 18.something city, it has been pretty constant the four years and 37,000+ miles I have owned it. AC on probably 99.99999% of the time (live in Miami).
mcox522
New member
Snoranger
Member
I have fuel economy data on my 2015 4Runner from both winter/summer here in Cali...where cranking the window down just won't cut it! :-D
I dare say there is barely 1mpg difference over time...mostly city driving though.
It's hard to compare WINTER/SUMMER ... since we tend to do longer trips in SUMMER.
Using a coarse data CUT, SUMMER = MAY to SEP (where AC is on almost all the time) and WINTER = OCT to APR (where AC is probably on a couple of times)
MPG SUMMER = 17.217
MPG WINTER = 15.967
DELTA = 1.25MPG
CONCLUSION
Can't separate WINTER/SUMMER gas impact compared to short/long trips or impact of AC but you can see last few tanks were long ass trips, dragging the average up!
It stands to reason that there will be some loss with the AC, but the loss will not be much. In the above mentioned post, summer and winter fuel mix have a larger impact than the AC, which could easily account for the 1.25MPG. I'm not saying it does, but I would suspect that plays a larger role than the AC.
Keep in mind also, that anytime you run the front defroster, it is actually running the AC to dehumidify the air. Just food for thought.
wshiverick
New member
The mpg calculated by the Ecm that displays on your dash is wildly unreliable. If you really want to know you've gotta calculate it when you fill up with quanity against mileage. But even that assumes you have stock tires, vent and purge valves working flawlessly... if you're concerned about mileage get a Prius.
Air temperature and humidity have a huge impact on fuel economy, and gasoline sold in the winter is a different blend than other times of the year. All have a significant impact on fuel economy so you can't really pull out the difference when also comparing across seasons.
Although AC is becoming more efficient over time (combination of higher efficiency compressors and better insulation and solar reflective coatings), it's could still be more efficient, in a dinosaur like the 4Runner, to drive with the windows open rather than with AC. (https://www.sae.org/publications/technical-papers/content/2013-01-0551/).
Personally, this last summer was hot and humid as *#$%@ and I decided I'd rather pay more in gas to take a small break from constant sweating...
Although AC is becoming more efficient over time (combination of higher efficiency compressors and better insulation and solar reflective coatings), it's could still be more efficient, in a dinosaur like the 4Runner, to drive with the windows open rather than with AC. (https://www.sae.org/publications/technical-papers/content/2013-01-0551/).
Personally, this last summer was hot and humid as *#$%@ and I decided I'd rather pay more in gas to take a small break from constant sweating...
1000MPH
Senior Member
Mine is very accurate. I hate this argument: A Prius won’t get me where I want to go but a more efficient 4Runner will get me there and back out again.
That being said, A/C has little effect on MPGs compared to other factors.
Things I will not give up for better gas mileage: 4Runner capabilities, comfort, speed (as in driving slower than the speed limit). Most other stuff is negotiable.
Keep in mind that paper's conclusions are at 100% compressor duty cycle, something that will never be seen except in transient conditions. They mention they used a 1500W heater in the car to try and achieve it.
Although they gave some data at 50% duty cycle (still high for interstate travelling), they don't compare that data to windows down.
The paper does give data, but not really useful data - because that would be hard. eg. Calculating realistic AC power consumption usage and quantifying that.
I've got a Prius v and can access the compressor power PID. Max compressor input power is 4hp. On interstate trips it'll generally run around 1-1.5 hp.
Assuming 20 hp is required to overcome rolling/air resistance at 70mph, that's knocking down my mph 5-7.5%. On a much bigger vehicle such as the 4Runner, it'll be a lot less. I'm guessing you'll need ~35 hp @70mph, so the AC drain would ~1.8-4.2%.
You can also look at a typical compressor performance curve.
www.sanden.com/objects/PXV16_Performance.pdf
At 2600rpm (2000 engine rpm, aka 70mph), this 163cc compressor (same displacement as ours) will eat 4kW (3hp) assuming a high side of 242psi and a low side of 29psi. On the interstate, you will never see anything near 242 psi due to all of the air flow. That means you will also less than 4kW of power used at 2600 rpm, and that's at 100% duty cycle.
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