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Discussion Starter #1
In one Mythbuster episode they test this, and determine that above 50mph it's more fuel efficent to use the A/C than have the windows down.

They used trucks though. How much HP does the A/C rob on the 4.6L V8, and when would be the better time to use it without burning gas like crazy?
 

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It must just be were I live and what i am used to, but if it is under 90 degrees, it is generally windows down, unless out on the interstate or at 50 mph+ for any amount of time. 90-100 it depends on things like humidity and if I am moving fast enough. 100+ it is all AC all the time!

With my 2000 GM and the auto climate control, it is always set to 75 or 76, and does whatever it needs to maintain that temp. In my 97 Cougar, with only semi auto climate control, I tend to use the windows more often. The AC just went out in my 89 Cougar, so it gets used any time it is under 90 (so I can use it in the morning until around 8 am, then it is too hot).

Screw worrying about the 1-2 mpg difference between AC on and off (and other factors like wind drag) it is all about my comfort and wind noise.
 

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Gas is expensive and I only get about 10-15 mpg(guess based on previous calculations of 9mpg in the winter, and a noticed improvement in warm weather) I have to worry about 1-2mpg.

I don't like how it turns the A/C on to keep the air temp coming out of the vents the temp thats set on the controls. Why doesn't it just let outside air in to cool hot air, and add heater to warm cool air like older cars did.

I don't understand the need to have the A/C come on to keep the air coming out of the vent at 20C or something.
 

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If your getting 10-15 mpg you have much bigger issues than a/c.

If you want air from outside to cool the hot air inside, open the windows. Your not going to magicly get the air outside to cool the air inside via the vents without a/c.

There is nothing different between these systems and ones from 20 years earlier besides round knobs and a digital display.
 

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Gas is expensive and I only get about 10-15 mpg(guess based on previous calculations of 9mpg in the winter, and a noticed improvement in warm weather) I have to worry about 1-2mpg.

I don't like how it turns the A/C on to keep the air temp coming out of the vents the temp thats set on the controls. Why doesn't it just let outside air in to cool hot air, and add heater to warm cool air like older cars did.

I don't understand the need to have the A/C come on to keep the air coming out of the vent at 20C or something.
Your in Canada right? Are we talking liters per kilometer, or actual miles per gallon here?

Cause if your acutally getting 9-15 mpg in a 4.6 bird you definitely have bigger problems than the AC. I live in Las Vegas NV. It gets HOT here. The worst mileage I ever got in my 94 was 17-18mpg. But it was usually more like 20-22 with the AC on.
 

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Discussion Starter #9
I'm in Canada, but this was converted form litres to MPG by racecougar. It was a thread on cougarnuts that originally determined this estimate. It was also winter.

Ive seen improved mileage now. I was going about 50km before the needle would be at 3/4 tank, and now its around 120 or more before I'm at 3/4 tank.

Depends on driving conditions too.
 

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Me and my brother are totally indifferent. He rips out the AC out of any car he gets (Mustang). Whereas me, I use the AC 80% of the time because I like being comfortable. Plus, I want to take advantage of the AC in the Bird before all the freon leaks out by the end of Summer lol.

Last owner said it lasts about 4 or 5 months so I took his word for it.
 

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So your guessing the fuel consumption?

As long as your odometer is accurate, it is easy to figure real mileage, and not guess about approximate distance to a certain level shown on the gauge.

Reset the trip and fill it up. Drive until you fill it up again, note how much gas you put in it and how far you have driven. Divide kilometers by liters. If you want mpg then go to google and put in the numbers, like "7.4 kpl in mpg".

Obviously it depends on driving conditions and such, but just don't use your AC if you feel you are taking that big of a hit on mileage. If you have SATC then set it to Vent and auto, however if it is not possible to reach the desired temp with ambient air, then you would need to use the AC.
 

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Discussion Starter #12
Right now I'm guessing yes. The 9mpg figure was an actual calculation done by the method you just mentioned. but it was done back in the winter when the fuel mileage is worse anyway.

I just removed the silencer on my airbox today, now its open right into the valence, I removed the entire elbow. I also cleaned my MAF. not sure if its gonna help anything, but it couldn't hurt at the very least.
 

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My SC only get single digit MPG at WOT and I run out of driveshaft before it matters too much (373 w/ stock D/S).

If really want to know its either a simple experiment like Mythbusters did or Calculus with drag coefficient (Cd). Personally I'd go for the math, so you find the tipping point in regards to speed, well guess would also need to figure the change in Cd with windows down.

The number I've always heard is ~45mph is the tipping point. Faster AC is better slower windows are.

Remember since we're so regional diverse our drops will be different but % should be approx the same.
 

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I got 21 MPG going to Seattle. No EGR, 150MPH runs and then driving 15MPH for 2 hours up and down a mountain in a blizzard. This included a 20 mile 130MPH cruise to get turned around and to an accident to help out. So if you're getting 9 there is some serious issues.
 

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First, take the dead heavy body and safe out of the trunk. If this doesn't apply to you... you are getting close to 1/2 the mileage you should. Check the treads in the 4.6L official MPG thread. (here) I haven't put my figures in as I have a ScanGauge, live in Houston. ( flat as a pancake) and you could say I'm a almost a Hyper miler. Not happy unless I see closed to 30 miles per gal. Only time I smile comes is when I see it pegged at 99.99 mpg.
 

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With me, I honestly can't tell if there's a difference. My MPG varies so darn much as it is... I've seen 30 MPG on the highway (this was last summer when the a/c was out of commission) down to 22 MPG on the same highways. On the streets I see as low as 16, up to 22. With the A/C on the last time I took that highway trip I think I saw 24-25 MPG... Plus the whole purpose behind my fixing the darn thing a few months ago was so I could use it.
 

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no way these cars get 30mpg on the highway.
the figures are based on the one short tank fill up and never repeated.
like the 12 second drag cats that get 20 mpg with 4.30 gears.
Mabey 26 on the highway with no a/c and going 55 mph.
The story I read is I got 30 one time. Never repeated.
LIke the time I got 18 mpg hauling my cougar on the trailer across Alligator Alley at 70 mph.
Short fill ups.
 

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R429460 I'm going to retype all this. I don't wanna let my ******* side show.

you would be sadly mistaken my friend. My cougar got more than 30MPG on the interstate several times. GPS kept the miles and I always fill up to the top. As in it's sitting in the bottom of the neck above the fill flapper. My brother's gotten 32MPG in his Mark VIII. Just because YOUR car doesn't get 30MPG on the interstate doesn't mean others don't.
 

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The best my stock 95 xr7 got was 25 on I75 in south fla going to tampa from fort laud. 70 mph.In 2003. Still doubt those 30 mpg'ers.
But, oh well.
These 30 numbers are not all the time.
Just short fill ups.
'cause I'm the OCD guy who checks every fillup.
Once I had 27 on a short fill.
 

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no way these cars get 30mpg on the highway.
the figures are based on the one short tank fill up and never repeated.
like the 12 second drag cats that get 20 mpg with 4.30 gears.
Mabey 26 on the highway with no a/c and going 55 mph.
The story I read is I got 30 one time. Never repeated.
LIke the time I got 18 mpg hauling my cougar on the trailer across Alligator Alley at 70 mph.
Short fill ups.
Never repeated? I wouldn't say that.... Examine my figures from last fall. Yes, a relatively short fill-up, but the figures don't lie. The trip is about 40% 68 MPH, 50% 60 MPH and 10% city driving.

Best trip 8/30/08, 235.9 miles traveled, fuel used 7.916 gallons, MPG 29.8. Second best, 9/20/08, 238 miles traveled, fuel used 8.202 gallons, MPG 29.0. Third best, 9/23/08, 234.7 miles traveled, fuel used 8.213 gallons, MPG 28.6.

Those are the best three. The next highest comes in at 25.6 MPG, but that was that same highway trip and then a weekend's worth of city driving on one fill up- so the city to highway driving ratio for that fill-up was closer to 70% highway/30% city rather than the 90% highway/10% city from before.
 
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