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My car is messing with my emotions this morning. At one point it said 29MPG. I only have around 325 miles on the ODO on my new hatchback '13. That was just from this morning though, on average it says I get between 21-24MPG. Although I calculated my MPG at the pump on my first fillup I average 23MPG, just 1 below what the meter in my car said I was getting.

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By my own calculations my stock 2013 WRX has been giving me around 18 mpg city and 26 highway, though I could probably push the highway number up a little higher since I'm finished with the break in and can use cruise control now. The readings from the computer have been about 1 mpg more than what I've actually been getting.
 

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As far as running the A/C wasting gas while driving... didn't myth busters prove that to be wrong? I believe they ran a car around a track from full to empty with the A/C on and then with it off and saw no difference or very, very little. I do agree that other electronics would do a very slight amount but most of it comes down to whether you are driving like a nut or not. So far I am averaging 20.4-23.8 in the 800 miles I've had the car. These are above the average that the sticker from the vehicle says is average for the vehicle so I am pleased.
 

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Discussion Starter #244
I believe it was A/C on with windows up vs A/C off with windows down.
 

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As far as running the A/C wasting gas while driving... didn't myth busters prove that to be wrong? I believe they ran a car around a track from full to empty with the A/C on and then with it off and saw no difference or very, very little. I do agree that other electronics would do a very slight amount but most of it comes down to whether you are driving like a nut or not. So far I am averaging 20.4-23.8 in the 800 miles I've had the car. These are above the average that the sticker from the vehicle says is average for the vehicle so I am pleased.
I believe it was A/C on with windows up vs A/C off with windows down.
Yes that is correct. They saw about a 10% decrease in gas mileage from either setup/situation, which aligns with the general % I've always heard.
 

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Very good write up.

Ive been contemplating writing a similar write up for the diesel industry on this same thing.

I get calls all year long with people asking why their mpg has suddenly dropped.

There is so many things to factor, driving style, driving condition, outside temp, etc etc

Driving style, are you a lead foot or drive like grandpa?

Driving condition, are you driving 100miles one way to work, or are you making a 2 mile drive down the road? this greatly effects average mpg. Ive found that with my truck under LIGHT acceleration the instant mpg is about 2mpg. but once i get rolling its around 30ish. I do about 12-14 city driving and 20 on the freeway. so frequent stops will greatly reduce mpg. Also are you on the flats of Nebraska or are you in the rolling hills of Kentucky?

Outside conditions seem to be where i find most of the losses im mpg come from in my customers. When its 100+ outside I run the AC on max, and then due to the thin air the truck is a doggy, smoky pig which thus uses allot of fuel. Same goes for the winter time. Weight of snow on the truck, running the defroster, letting the truck warm up for 15-30min before i drive it.

essentially i have given up on mpg and just fill the damn thing up when the light comes on. lol
 

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Wow... You get 30mpg in a diesel truck? What kind of rig is it?
 

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thats just a instant rolling down the the road at 35ish. the average is 12-20 depending on what im doing.

but its a 640hp 06 Duramax
 

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I am seeing 21mpg going 80, and get it up to 27/28 by going 65... doing some maths....

If I go 80 I save 50 min a week total commuting, or save 10 bucks hmm lol

But been averaging 19.5 per tank...
 

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Discussion Starter #250
I got 17.2mpg today for my first day of driving my new jeep wrangler. Not too shab for a 285hp v6 pushing around a 4000lb brick.
 

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Well, if I was "hyper miling" I guess I could attain 25-27mpg even if my total mileage was at below 2500 miles.... I'm averaging 21 to 23 mpg since the rex was "broken in"..... Gradual increase thus far which is pretty good considering the fact it sees a lot more demand for boosting and brisk acceleration on my commute.

I'm hoping to see a little more improvement on the highway cruises as the odo nears 10k




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I am a traveling sales rep. Today after 230 miles round trip commute I averaged 24 mpg. 93% of which was highway driving.

I coast when I can. Go the speed limit, and stay out of boost.

However I'd love to know which is more fuel efficient. Normally I'd do 73 in a 65. But today I did 66 in a 65. I'm no math wiz so I'm not sure how to figure which is more efficient.

Maybe tomorrow I'll see my mpg on my way to work on the interstate @ 73. Then reset my odometer on the way home and see my mpg @ 66. I'd assume 66, but we'll see. Note: I'll reset the odometer when I'm up to speed and in cruise control.



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However I'd love to know which is more fuel efficient. Normally I'd do 73 in a 65. But today I did 66 in a 65. I'm no math wiz so I'm not sure how to figure which is more efficient.
Has more to do with science than math. This is where the drag coefficient comes into play.
 

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As far as running the A/C wasting gas while driving... didn't myth busters prove that to be wrong? I believe they ran a car around a track from full to empty with the A/C on and then with it off and saw no difference or very, very little. I do agree that other electronics would do a very slight amount but most of it comes down to whether you are driving like a nut or not. So far I am averaging 20.4-23.8 in the 800 miles I've had the car. These are above the average that the sticker from the vehicle says is average for the vehicle so I am pleased.
Mythbusters a/c episode was a highly flawed test... like most of their shows. But it makes perfect sense. A/C off with the windows up should give best mileage, even if so minute it can't be measured. A compressor under load has much more resistance, that saps power, than a compressor pulley without it's clutch engaged. This difference certainly isn't anywhere near 10% in a car this powerful. Maybe in a beetle... I'll take not being a sweaty bastard vs < 5% MPG hit any day.

The only way high electrical use would use more MPG is if you installed a new alternator... even then... the rotational resistance of an alternator is negligible and certainly doesn't change dependent upon much of it's potential power use.
 

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The only way high electrical use would use more MPG is if ....
Do you know GENERATORS? I mean the ones at like hospitals. There is a very real relation between electrical load and HP generated (used) and related fuel consumption.
And the alternator is a REAL generator, even if it's not very large.
 

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Do you know GENERATORS? I mean the ones at like hospitals. There is a very real relation between electrical load and HP generated (used) and related fuel consumption.
And the alternator is a REAL generator, even if it's not very large.
Sure, draw does have an effect on rotational resistance. Is it even enough to mention when discussing MPG?

I mean, you can power a whole concert off of a ****ty lawn mower generator...

You're not even really running an audio system off the alternator, really. You're just using the alternator to charge the battery. I guess having an audio system might cause your battery to need to charge longer to remain full... I doubt you'd ever be able to measure an MPG difference unless you did a massive or second alternator upgrade.
 

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Take it this way: The alternator has probably about 60Amp output. At 12V that's (12x60) 720 Watts. 700-some Watts equals 1 HP. That's the load and related fuel the alternator will take. Pretty simple, really. The rear defroster probably draws 15 Amps alone. Lights add up to maybe 120W (10Amps) Blowers, secondary air pump, fuel pump etc all draw off the electric system. The alternator supplies all of that until it reaches it's limits. If more is needed the battery delivers that until load goes down and then the alternator delivers it all AND charges the batt back up. It makes no difference if the alternator charges battery and battery supplies all of alternator supplies all including charging the batt. It all ends up the same. It's like having a waterline going into a bucket and having a faucet in the bottom of the bucket...
A/C, power steering and so on only add to the additional loads in a straight mechanical way...
 

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Last Night, I average 30.6 MPG @ 65 MPH :)

-Time: 11:05 PM/PST. Outside Temp: 68 Degrees.
-Traveled 60 Miles to achieve 30.6 MPG.
-Cruise Control was set @65 MPH
-Stock Tune
 

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Last Night, I average 30.6 MPG @ 65 MPH :)

-Time: 11:05 PM/PST. Outside Temp: 68 Degrees.
-Traveled 60 Miles to achieve 30.6 MPG.
-Cruise Control was set @65 MPH
-Stock Tune
Nice.

I was close to that the other night, until I hit the smallest hills. People that live in flat areas certainly have an advantage here. ;)
 

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MPG update

Thought I'd post an update since my last plot is nearly a year old. Two things happened about 10k miles ago. I moved into town (less highway driving) and my check engine light has been coming on and I've been experiencing rough idle.
2011 wrx - stock

miles per gallon 2.jpg

edit: for clarity
 
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