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Something is definitely wrong here.

I recently did three trips in the last week that were about 90% highway each (NY to DC - 270 miles, DC to NJ - 230 miles, and NJ to DC - 210 miles).

Speed was an average 75-80 MPH. I run 89 octane, and despite it being winter gas, my MPG for all three trips was less than 20. About 19 and change.

That was with a change to clean oil (Motorcraft 5W30) and a Seafoam treatment right before the NY-DC trip.

My city mileage (I've been keeping track for the last year or two) is in the low 14s. Even with summer gas, my highway mileage (I took a road trip to Pennsylvania and back) was sub-20.
Every car has a 'sweet spot' for MPG, after which the increases in speed cause your MPG to drop like a rock. I'm not sure what the bird's peak MPG efficiency speed is, but it's likely around 55 MPH. At 75 MPH, you're getting about 15% less fuel economy than you are at 60. At 80, that would be even worse. So with a little math, at 19 MPG running 80 MPH, theoretically you'd be getting 22 or better MPG at 60 or MPH. That goes right in with my MPG; I took a 240 mile round trip this Sunday, 90% highway and got 21.9 MPG with an average speed of about 65 (alternating between 60 and 70 on different highways). I also have been getting 15-18 MPG city lately. I expect that to jump up to the mid-high 20s and low 20s, respectively, when the warm air returns. And I'm running the super cheap brandless 10W oil and 87 octane.
 

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funnyfingers- I thinks it's just my heavy foot and mainly city driving. On the highst I got was when I took a roadtrip one day to pisgah, ia. I think I got like 23... but that tank was still mostly city. I think the 89 is E10, I don't know about 91.
 

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Engine: 4.6L
City MPG: 18
Highway MPG: 25
Combined MPG: 21
Fuel Used: 87
Average Highway Cruise Speed: 65 MPH
Average Climate: 20* - 100* F, ever changing
Mods: JMOD, Glasspack mufflers, air silencer delete, K&N Panel filter
Mileage on the Engine: 130,000
 

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Summer Gas! Yea!

Went thru the first two tanks of summer gas last week, and mpg went from ~20 to over 25mpg, both cars!

I've been trying to figure out what the deal was for a while, because the gas mileage has been crap since last summer... Apparently, the gas here has been crap since last summer.

Prices here jumped last week to 2.19 for premium, and that was the change to good gas.

The guy that checks the pumps is an old-timer with the company, and said that below $2 a gallon, they use more alcohol instead of more expensive additives... IDK if that's true, but he has a fleet of old cars he keeps, and supposedly the only reason for this particular gas station is for his cars. (small town, huh? :D ) It's much better gas than everywhere else, and it doesn't usually have alcohol in it. My bikes hate it when I fill them on a ride somewhere... :)

5 mpg for .20 cents is a good deal for me, lol.
 

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I drove from Omaha to KC, around town a bit, and back home on nearly a single tank (375-400 miles, or around there). I had to refill in Council Bluffs, I probably could have made it across the river, but it was getting late and I didn't want to worry about it. Did just shy of 26 mpg. That's the best I've I done.
 

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Best I ever did was just shy of 30. Took a 245 mile round trip on less than a half a tank. Boy, did it ever surprise me.
 

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Engine: 4.6L
City MPG:15
Highway MPG: 21
Fuel Used: Whatever regular is around
Average highway speed: 80
Average Climate: Florida... is hot
Mechanical Mods: Cold air intake, Flowmaster exhuast
Milage on the engine: 35,000
Comments: I have no idea what's wrong with my gas mileage. Anyone care to shed some light?
__________________
 

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Guess I'll update since my car has changed a bit

Engine: 4.6L
City MPG:18
Highway MPG: 26
Fuel Used: Premium 93
Average highway speed: 80
Average Climate: warm-hot currently
Mechanical Mods: PI intake, 80mm maf, #24 injectors, True duals with high flows, semi J-spec 2000 GT trans, 3.55 gears, Tune(by me), 255mm tires, ~100 lbs of total weight removed
Mileage on the engine: 87,000
Comments: Tuning made the biggest impact and I'm still learning as I go.
 

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1,606 Posts
95 Mark VIII
City MPG: N/A
Highway MPG: 27.1
Fuel Used: Premium
Average highway speed: 70
Average Climate: roughly 65-70
Mechanical Mods: stock motor, removed air silencers; stock 2 cats dual 2.5" double x pipe midmounted, slight jmod
Mileage on the engine: 158K
Comments: yay
 

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2,019 Posts
1996 tbird lx 4.6
city 14 mpg.
highway 20 mpg
75 mph highway mph
mods sc 3.73 gears 400 hp to the tires

1995 tbird
4.6
150k miles
stock 3.27 gears
city 17 mpg
highway 26 mpg
80 mph average
 

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984 Posts
97 T-Bird
Engine: 5.0L-2V Big Bore
Combined MPG: ~12.5 observed
Fuel Used: 92 Octane
Average Highway Cruise Speed: 75 MPH
Average Climate: Michigan - your guess is as good as mine
Mods: SVO blower, Comp XE274H cams, 3500 stall TC, 4.10 Gear, Kooks headers with true duals, water/meth injection, cold air intake and many, many other powertrain and chassis revisions
Mileage on the Engine: approaching 2,000
 

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51 Posts
Stock 1994 Thunderbird
4.6, 3.08 gears, cheap gas.
No modifications yet, just very well maintained. Shift kit in the 4R70W.
18-20 mpg for local country driving and some highway. High-20's on long trips.
 

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30 Posts
Engine: 4.6
City MPG: 16
Highway MPG: 20
Fuel Used: 89
Average highway speed: 70
Average Climate: varied
Mechanical Mods: none
Milage on the engine: 151K
Comments:
 

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1,807 Posts
1995 T-Bird

Engine: 4.6
City MPG: 21-22
Highway MPG: 30
Fuel Used: 87
Average highway speed: 74
Average Climate: varied
Mechanical Mods: K&N, new MAF
Mileage on the engine: 193K
Oil: Havoline 10W30

Comments: Putting on a new Advance Auto MAF increased hwy mileage 2-3 MPG! I got 30 MPG avg over 1400 miles of hwy driving, mix of hills and flat.

The car (along with every car I ever had) has always gotten better mileage in the summer, even with the A/C on 90% of the time!

Al
 

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Guess I'll update since my car has changed a bit

Engine: 4.6L
City MPG:18
Highway MPG: 26
Fuel Used: Premium 93
Average highway speed: 80
Average Climate: warm-hot currently
Mechanical Mods: PI intake, 80mm maf, #24 injectors, True duals with high flows, semi J-spec 2000 GT trans, 3.55 gears, Tune(by me), 255mm tires, ~100 lbs of total weight removed
Mileage on the engine: 87,000
Comments: Tuning made the biggest impact and I'm still learning as I go.

ppffttt....some of that tune is by me! :tongue:
 

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11,961 Posts
yeah we appreciate your improvements :) Both of us. I'll update mine when I get to OK.
by the way, if I were you, i wouldnt run my EGR settings....your ported intake ports by now are the size of stock NPI ports.....lol
 

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175 Posts
Engine: 4.6 stock
City MPG: 19
Highway MPG:19
Fuel Used:Whatever is the cheapest
Average highway speed: 65-80 mph
Average Climate:warm to hot.. SF bay area
Mechanical Mods: K&N drop in
Milage on the engine: 123,xxx
Comments:
My driving is basically get up to highway speed for a mile or two and stop for a stoplight. Repeat up to 10 times each way. It's horrible. Speed, stop, speed, stop, etc..

This is my first tank of gas since I "rescued" this car.. Was in BAD shape.. Plug wires were in pieces, front o2's were bad, plugs pretty much wasted, lots of vacuum leaks..

Edit: last tank was 17.9 mpg. This tank is looking worse, traffic is horrible and the skinny pedal has been used a lot the last couple days.
 

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2,545 Posts
ahah my EGR hasn't worked right since I started fiddling with it. As soon as I get home I'm putting a Ford DPFE sensor on it and finishing up a tune from scratch now that I've got a dongle to use LOL. Only took me 6 months to order a new one. Also I'll be able to fix my exhaust leak and degree in the cams. As for the intake. I like my Gas mileage. If it gets carbon build up... welll hey. That's what Sea foam is for :)


by the way, if I were you, i wouldnt run my EGR settings....your ported intake ports by now are the size of stock NPI ports.....lol
 

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124 Posts
1996 Thunderbird LX "Sport"
Bone stock no mods

Engine: 4.6
City MPG: 14 (heavy right foot)
Highway MPG: 26
Fuel Used: 87
Average highway speed: 75mph
Average Climate: COLD! very very cold!
Mechanical Mods: none yet
Mileage on the engine: 132,000
Oil: Motocraft 5w20

Never even had the spark plugs changed. (because they are corroded into the head's) PI swap here i come =P
 
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