VW Vortex - Volkswagen Forum banner
Cancel
Create thread New Garage Forums

What is "Normal" Fuel Economy Loss When Using A/C?

Jump to Latest
1 - 20 of 66 Posts

UncleJB

· Registered
87 Jetta Coupe, 88 Cabriolet, 15 Golf TDI Sportwagen, 22 GMC Sierra 1500 Duramax
Joined
·
29,027 Posts
Discussion starter · #1 ·
I am not normally an A/C guy. I like to have the window cracked or down when out on the road as much as possible.

That being said, it has been hazy, hot, and humid here in the Northeast for the last week and I have been running the A/C when wearing my work clothes because its too damn hot.

Yesterday I took my wife's car to a meeting in the afternoon and ran the A/C on the way. The car is a 2008 VW Passat Wagon 2.0T/6MT and usually averages mid to low 30's (MFA indicated).

As I was driving I realized the average wasn't climbing above 24-25mpg. I have some materials to be delivered in the back, so at first I thought it was the weight.

Well, it rained while I was in the meeting and cooled down some, so I drove home with the windows down. The same trip, same route and basically same speeds I got 35mpg on the return. Again this is all MFA indicated, but is 10mpg "normal" for running the A/C?? Like I said, I rarely if ever use it so it was a surprise to me.

Any ideas? Other than don't use the A/C. ;)
 
#4 ·
That's interesting. I have a different experience. My summer mileage with the air on is usually higher than winter mpg with it off (likely due to seasonal fuel blends, air density and different frictional forces). I haven't bothered to compare air on to windows down summer mileage, but I suspect that the air on beats windows down because of aerodynamics.
 
#5 ·
A car review video had mentioned that wind resistance from windows down on highway uses more fuel then windows up with a/c. Idk. IF that's true, yours might be that weight you mentioned in the back.

Did it just start happening?
 
#6 ·
Exhaustdd said:
A car review video had mentioned that wind resistance from windows down on highway uses more fuel then windows up with a/c. Idk. IF that's true, yours might be that weight you mentioned in the back.

Did it just start happening?
Click to expand...
Wind resistance or not my brick of a hatchback cannot reach as high a tank average running AC on the highway vs windows down. But as stated humidity is no time to play macho sweat builds character man.
 
Discussion starter · #9 ·
Vash350z said:
This, i would imagine if you hand calculated it, it would be closer to the above post.
Click to expand...
I know the MFA isn't "great" at indicating actual mpg, but it is usually within a couple mpgs of actual. I can't imagine that it is just off by 10mpg.

Exhaustdd said:
A car review video had mentioned that wind resistance from windows down on highway uses more fuel then windows up with a/c. Idk. IF that's true, yours might be that weight you mentioned in the back.

Did it just start happening?
Click to expand...
Its not so much that I am trying to figure out if windows down or A/C is more efficient, more that I am surprised at such a huge drop in fuel economy.

The materials were in the car going both ways yesterday, so it can't be that. I achieved the usual 34/35mpg average on the way home with the gear in the back and no A/C on.

2.0T_Convert said:
Wind resistance or not my brick of a hatchback cannot reach as high a tank average running AC on the highway vs windows down. But as stated humidity is no time to play macho sweat builds character man.
Click to expand...
Amen to that...I know you are going through the same weather pattern. I almost preferred the rain. :what:

WaWaMKVDub said:
http://dsc.discovery.com/tv-shows/mythbusters/mythbusters-database/ac-vs-open-windows.htm
Click to expand...
Cliff notes? I am working on my laptop at McDonalds... :laugh:
 
Discussion starter · #10 ·
Meant to mention, this is my wife's car, so I don't spend a ton of time in it. She did say she thought the fuel went much faster with the A/C on, but doesn't normally look at the MFA.

I do almost always drive with the driver's window down and have never noticed such a drop in mpgs. Regardless, I will always drive with the window down either way. I even keep it at least cracked all winter long. :laugh:
 
#13 ·
2.0T_Convert said:
Wind resistance or not my brick of a hatchback cannot reach as high a tank average running AC on the highway vs windows down. But as stated humidity is no time to play macho sweat builds character man.
Click to expand...
But if it's true, it's going to be a long summer for macho sweat man. Having to run around without AC AND the windows up is going to be a hard pill to swallow.

Image
 
#14 ·
Depends on:

Engine size (fuel consumption)
Design of electrical system used to cycle the A/C compressor, which is a function of the compressor design

Ex. I've driven two of the same model yr VW Passat - One with a 4-cyl. one with a V6. The V6 had a lesser fuel economy penalty when running the A/C conpared to the 4-cyl. Could be due to the fact that when the A/C compressor clutch activates, it "burns" a greater percentage of available torque from the 4-cyl. compared to the V6...to compensate, you press the accelerator harder on the 4-cyl. and FE takes a bigger hit. 4-5 mpg in the V6...as much as 10-12 mpg in the 4-cyl.

Conducted tests in both cars repeatedly over a 3 mile stretch with conisitent results.
 
#15 ·
Electron Man said:
Depends on:

Engine size (fuel consumption)
Design of electrical system used to cycle the A/C compressor, which is a function of the compressor design

Ex. I've driven two of the same model yr VW Passat - One with a 4-cyl. one with a V6. The V6 had a lesser fuel economy penalty when running the A/C conpared to the 4-cyl. Could be due to the fact that when the A/C compressor clutch activates, it "burns" a greater percentage of available torque from the 4-cyl. compared to the V6...to compensate, you press the accelerator harder on the 4-cyl. and FE takes a bigger hit. 4-5 mpg in the V6...as much as 10-12 mpg in the 4-cyl.

Conducted tests in both cars repeatedly over a 3 mile stretch with conisitent results.
Click to expand...
no.
 
#16 ·
BigSkyGLI said:
I am not normally an A/C guy. I like to have the window cracked or down when out on the road as much as possible.

That being said, it has been hazy, hot, and humid here in the Northeast for the last week and I have been running the A/C when wearing my work clothes because its too damn hot.

Yesterday I took my wife's car to a meeting in the afternoon and ran the A/C on the way. The car is a 2008 VW Passat Wagon 2.0T/6MT and usually averages mid to low 30's (MFA indicated).

As I was driving I realized the average wasn't climbing above 24-25mpg. I have some materials to be delivered in the back, so at first I thought it was the weight.

Well, it rained while I was in the meeting and cooled down some, so I drove home with the windows down. The same trip, same route and basically same speeds I got 35mpg on the return. Again this is all MFA indicated, but is 10mpg "normal" for running the A/C?? Like I said, I rarely if ever use it so it was a surprise to me.

Any ideas? Other than don't use the A/C. ;)
Click to expand...
Mid 30s in a 6mt wagon? ***sucks teeth*** i don't know bud, that seems highly optimistic. Maybe freeway only, on level ground. I see around 32-33mpg tops in my sedan on the freeway, as soon as you introduce some stop and go traffic it drops like a rock. These DI 2.0s are nice on the freeway but they sip pretty readily around town, in the very low 20s from what ive seen. I usually average right at 23.5-24mpg overall, with around 70/30 freeway/bumper to bumper driving. Is this a TSI or FSI car? (they went TSI mid-way through '08 so it could be either). I've noticed my MFD to inflate mpg estimates by around 1-1.5mpg, so its fairly accurate.

Also, I don't notice any difference between AC on or off, usually because if its cool enough to go without it, the warm up times increase and the windows get cracked offsetting the lower parasitic losses on the crank.
 
#19 ·
ATL_Av8r said:
usually .5 - 1 mpg according to my mileage Excel spreadsheet when I glance at summer months vs other months.
Click to expand...
This

For a lot of car designs, you get better fuel economy with the windows rolled up and the A/C on than with the windows down and A/C off.

For those of us in the cold weather part of the country, winter is the time of poor fuel economy. Much more aerodynamic drag in subzero low-humidity air than low density hot/humid air. My GTI loses 5 mpg at -10F at 75 mph compared to summer driving. I'm sure ATL-Av8r knows all about "density altitude" calculations. The wimpy single engine planes I fly won't get off the ground on a hot-humid summer day unless you go with half fuel.
 
#20 ·
2010 GTI, 6 MT

~5 MPG hit with the AC on.

Something like 1-2 seconds slower to 60 as well, and that's regardless if you have the AC on or its just a hot (80* F or higher) day. My car has absolutely no balls in the heat.
 
1 - 20 of 66 Posts
About this Discussion
65 Replies
37 Participants
Last post:
Snake Hips
VW Vortex - Volkswagen Forum
posts
85M
members
1.5M
Since
2001
A forum community dedicated to all Volkswagen owners and enthusiasts. Come join the discussion about performance, builds, modifications, classifieds, troubleshooting, maintenance, new releases, and more!
Full Forum Listing
Explore Our Forums
The Car Lounge Golf IV & Jetta IV Golf III & Jetta III Golf II & Jetta II Golf IV/Jetta IV Parts