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Old 07-27-2013, 08:25 AM   #4601
Caocao
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A lot of folks on the forums have reported that both their mpg gauge and odo are 2 to 3% inaccurate. I guess there some recalibrating that can be done at the dealer. If you have non stock tire size that would also add to your problem.
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Old 07-27-2013, 08:35 AM   #4602
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Understood. My tires are stock but I think the Sport Premium are bigger than the lower trims. How much would this cost at the dealership?
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Old 07-27-2013, 08:57 AM   #4603
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Originally Posted by Dill-Ag13 View Post
Understood. My tires are stock but I think the Sport Premium are bigger than the lower trims. How much would this cost at the dealership?
Should be free under warranty
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Old 07-27-2013, 10:05 AM   #4604
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Originally Posted by Dill-Ag13 View Post
Understood. My tires are stock but I think the Sport Premium are bigger than the lower trims. How much would this cost at the dealership?
Figure out your odometer error first.

For example my car was always about 5-6% below indicated mpg, but my odometer error was 2.9% low (now 2.7% as I have 25k on the tires). I had the dealer adjust the display by 3%, which combined with the error makes it spot on accurate, I usually even beat the indicated mpg by .5mpg now
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Old 07-27-2013, 06:00 PM   #4605
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Just spent two hours on the interstate and man, a/c really KILLS mpg's. Its gotta be a good 8-10% at least.
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Old 07-27-2013, 06:16 PM   #4606
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Quote:
Originally Posted by flyboy1100 View Post
Figure out your odometer error first.

For example my car was always about 5-6% below indicated mpg, but my odometer error was 2.9% low (now 2.7% as I have 25k on the tires). I had the dealer adjust the display by 3%, which combined with the error makes it spot on accurate, I usually even beat the indicated mpg by .5mpg now
Wouldn't just leaving it alone mean you were putting less mile on your car? Not being sarcastic... if that is true, I am going to leave mine alone... don't care what Display says as I always hand calculate.
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Old 07-27-2013, 06:56 PM   #4607
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For the 5MT drivers who mostly wouldn't go over to the CVT thread, I graphed BigFatHorse's big dataset of fuelly data:

http://forums.nasioc.com/forums/show...5&postcount=35

Quoting myself
There are 140 drivers in the database with CVT's and only 38 with 5MT's. If you kind of step back (well, or sit back) and look at the big picture, you can see the 5MT's, despite that enthusiasts generally prefer manual transmissions, get better mpg with the Impreza. The average for this, the big dataset, is 27.7 mpg for the 5MT and 27.1 for the CVT's.

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Old 07-27-2013, 11:52 PM   #4608
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Just spent two hours on the interstate and man, a/c really KILLS mpg's. Its gotta be a good 8-10% at least.
File this under "Problems cars with the 2.5L engine don't have".

Still have my fingers crossed for Subaru to offer a 2.5L option on the 2014 model... I also wouldn't be disappointed to see Subaru utilize and "Eco" button like Honda that changes the engine mapping and A/C use patterns to allow for better MPG. They could tie this in with come CVT tuning to hold gears a bit long even if the car drops a couple MPH when going up a hill.

When you put the pedal on the floor in a Honda, it just turns off Eco so its not like you will run into a situation where the limited engine power causes an accident or anything.

Last edited by ocellaris; 07-28-2013 at 12:03 AM.
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Old 07-28-2013, 12:34 AM   #4609
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Originally Posted by vwgti123 View Post

Wouldn't just leaving it alone mean you were putting less mile on your car? Not being sarcastic... if that is true, I am going to leave mine alone... don't care what Display says as I always hand calculate.
The adjustment is only for the readout, it has nothing to do with actual odometer values as tampering with that is illegal.

Hand calc is only good when you know actual mileage per tank, if you haven't changed your odometer error, you are wasting your time and probably are getting somewhere in between indicated and your calculation
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Old 07-28-2013, 12:39 AM   #4610
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Quote:
Originally Posted by ocellaris View Post

File this under "Problems cars with the 2.5L engine don't have".

Still have my fingers crossed for Subaru to offer a 2.5L option on the 2014 model... I also wouldn't be disappointed to see Subaru utilize and "Eco" button like Honda that changes the engine mapping and A/C use patterns to allow for better MPG. They could tie this in with come CVT tuning to hold gears a bit long even if the car drops a couple MPH when going up a hill.

When you put the pedal on the floor in a Honda, it just turns off Eco so its not like you will run into a situation where the limited engine power causes an accident or anything.
Don't hold your breath

I know a/c saps power, I'm not convinced it is that high though, my most recent highway trip was pulling 32+@ 75mph w/ a/c on, with it off maybe just maybe I might have seen 33.5
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Old 07-28-2013, 03:16 AM   #4611
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Quote:
Originally Posted by 79letour View Post
Just spent two hours on the interstate and man, a/c really KILLS mpg's. Its gotta be a good 8-10% at least.
Yup. That's pretty much the experience I'm getting with my car.

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When air conditioning is in use, it's responsible for about 10% additional fuel consumption; if your 87 octane has 5-10% ethanol in it, you can expect another 15-20% drain on fuel consumption vs. straight gasoline.

That's more or less what I've found with my car. YMMV.
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Old 07-28-2013, 06:08 AM   #4612
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I don't see the a/c on its own being that much of a problem with my car. It's usually a few things together that does it for me (a/c, speed, wind, hills).
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Old 07-28-2013, 11:12 AM   #4613
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Originally Posted by flyboy1100 View Post
Don't hold your breath

I know a/c saps power, I'm not convinced it is that high though, my most recent highway trip was pulling 32+@ 75mph w/ a/c on, with it off maybe just maybe I might have seen 33.5
On a 10-20 mile, flat and level straigthaway, with cruise set at 70, I saw a regular 4-6 mpg drop on the readout simply by pressing the a button. I repeated this several times on my 5 hour roundtrip. Thats actually higher than 10%.
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Old 07-28-2013, 11:54 AM   #4614
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Originally Posted by 79letour View Post

On a 10-20 mile, flat and level straigthaway, with cruise set at 70, I saw a regular 4-6 mpg drop on the readout simply by pressing the a button. I repeated this several times on my 5 hour roundtrip. Thats actually higher than 10%.
The initial yes, but it comes back. There is no way my car gets 36+mpg @ 75 w/ a/c off. I only see that mileage at less than 70, I have 25k on the car now mostly highway so I'm pretty familiar with what it achieves

You can actually see the same kind of mpg drop by opening all 4 Windows too

Last edited by flyboy1100; 07-28-2013 at 04:30 PM.
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Old 07-28-2013, 12:19 PM   #4615
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I was seeing more like 27-28 with ac and 31-32 without. Windows remained up. All the variables were the same.
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Old 07-28-2013, 12:20 PM   #4616
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Lol opening all four windows gets dust all over my nice clean squeak free rattle free dash!
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Old 07-28-2013, 12:46 PM   #4617
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Lol opening all four windows gets dust all over my nice clean squeak free rattle free dash!
For now
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Old 07-28-2013, 01:26 PM   #4618
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I just went out to my "test track" (local 1 mile stretch of flat level ground) for gazintas*.

I was thinking the percentage difference in mpg would vary as the faster one goes the harder the engine works so the energy required to run the air conditioner becomes relatively less. I didn't get to equilibrium, but I think as the AC runs longer and starts switching the compressor off and on (more off at a faster speed) it would get closer to a constant dollars per time figure rather than dollars per hour.

When I turn on the AC:
At 40 mph my mpg decreases 8.7%
At 60 mph my mpg decreases 7.5%
At 80 mph my mpg decreases 3.8%

In all cases the money saved by turning off the AC amounted to less than 50 an hour, and averaged less than 30 an hour

*gazintas: 2 gazinta 4 twice, 4 gazinta 12 3 times, 3 gazinta 12 4 times, etc...
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Old 07-28-2013, 01:32 PM   #4619
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Originally Posted by stevehnm View Post
I just went out to my "test track" (local 1 mile stretch of flat level ground) for gazintas*.

I was thinking the percentage difference in mpg would vary as the faster one goes the harder the engine works so the energy required to run the air conditioner becomes relatively less. I didn't get to equilibrium, but I think as the AC runs longer and starts switching the compressor off and on (more off at a faster speed) it would get closer to a constant dollars per time figure rather than dollars per hour.

When I turn on the AC:
At 40 mph my mpg decreases 8.7%
At 60 mph my mpg decreases 7.5%
At 80 mph my mpg decreases 3.8%

In all cases the money saved by turning off the AC amounted to less than 50 an hour, and averaged less than 30 an hour

*gazintas: 2 gazinta 4 twice, 4 gazinta 12 3 times, 3 gazinta 12 4 times, etc...
My dictionary doesn't have this word..."gazintas"?
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Old 07-28-2013, 01:41 PM   #4620
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Old 07-28-2013, 02:02 PM   #4621
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So what are these "gazintas" supposed to represent in your test track findings?
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Old 07-28-2013, 02:07 PM   #4622
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spreadsheet cells?
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Old 07-28-2013, 02:37 PM   #4623
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spreadsheet cells?
Please make one so you're not the only one who understands what you're talking about
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Old 07-28-2013, 02:49 PM   #4624
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It's actually pretty simple concept, no need to analyze the piss out of it. The A/C requires power to the clutches on compressor. Just like the act of powering windows up and down ( not driving with them down, which was point made earlier- good point btw) there is more of an electrical draw on the car, hence more resistance so to speak on the alternator. That's why you see a drop in rpm before the computer recovers it by increasing injector duration. There is also some drag with the compressor running, but much of what you initially see is the alternator as I mentioned. That's why you also see the drag on engine with windows going up and down. When the compressor cycles off, there is less current draw, and compressor drag. You can leave the Ac off and take off while putting a couple windows up or down and while they are moving you can feel almost the same engine load as you do with the Ac on.

I just drove 276 miles with wife and 2 kids with air on while way at 70 half way, then close to 80 the rest. With a little big city driving ( Kansas City) and topped tank off at 34.6 mpg. That's with the roof rack off tho, rack zaps 3-4 mpg it seems even with Thule fairing
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Old 07-28-2013, 03:16 PM   #4625
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Originally Posted by G2Spfld View Post
It's actually pretty simple concept, no need to analyze the piss out of it. The A/C requires power to the clutches on compressor. Just like the act of powering windows up and down ( not driving with them down, which was point made earlier- good point btw) there is more of an electrical draw on the car, hence more resistance so to speak on the alternator. That's why you see a drop in rpm before the computer recovers it by increasing injector duration. There is also some drag with the compressor running, but much of what you initially see is the alternator as I mentioned. That's why you also see the drag on engine with windows going up and down. When the compressor cycles off, there is less current draw, and compressor drag. You can leave the Ac off and take off while putting a couple windows up or down and while they are moving you can feel almost the same engine load as you do with the Ac on.

I just drove 276 miles with wife and 2 kids with air on while way at 70 half way, then close to 80 the rest. With a little big city driving ( Kansas City) and topped tank off at 34.6 mpg. That's with the roof rack off tho, rack zaps 3-4 mpg it seems even with Thule fairing
So what's better for higher gas mileage, open windows or AC on?
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