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Official 4.6L MPG thread

240K views 323 replies 161 participants last post by  T6Rocket 
#1 ·
Hey guys, why dont we start an MPG thread?!?! A few people included myself have been interested in this subject for a while.
I think following form would help to get the thread organized correctly:

Engine:
City MPG:
Highway MPG:
Fuel Used:
Average highway speed:
Average Climate:
Mechanical Mods:
Milage on the engine:
Comments:


Here are mine :

Engine: 4.6L
City MPG: 15
Highway MPG: 19
Fuel Used: 89
Average highway cruise speed: 70MPH
Average Climate: Medium with alot of Rain
Mechanical Mods: Stock
Milage on the engine: 95,000Miles
Comments: New Fuelfilter helps
 
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#215 ·
My odo is broken too NetKeym, I do it the same way as you :) No matter what driving your doing, it always gives you the avg of what you have done for that tank, and therefore is the most accurate way of measuring Avg. MPG imo.
 
#216 ·
I guess I'll throw mine out there

City: 15-18
Highway:23ish
Combined:21
Grade: 87/89 (Depending on where I am)
No upgrades. Best I ever got was 31.5 MPG while driving through Nebraska heading back from Yellowstone it was like 317.2 miles on 10.07 gallons of gas (89 grade). It made me feel good that a v8 4000 pound car could get such good gas mileage. Average speed on that tank was approximately 75-80 MPH.
 
#217 ·
What is it about that state that makes for good gas mileage numbers? :) My best tank was there, coming home (to SD, at the time) from Colorado, and I didn't believe it when I filled up in Valentine and calculated 31-32 MPG.
 
#221 ·
My dad had it uphill both ways too; there's a valley between the family farm and the site of the country school.
 
#223 ·
96 THUNDERBIRD
stock:
13mpg city
14mpg hwy
87 an 89 octane

after head an intake work:
14 mpg city
lite hwy at 14 mpg
I know , I can't get it either
91 octane
Those are awful. Do you have any upgrades? Have you seafoamed/tuned up? Maintenance kept up with? Unless you drive like the gas pedal is an on and off switch you should be closer to 18ish on the highway.

I average 18 (on 89) and I do the worst kinda driving.. Car in my Info. I start it up 5 minutes before I leave, drive 6 minutes, then go to school for 8 hours. then drive it home without heating it up.
 
#227 · (Edited)
As an update.

Engine: 4.6L
City MPG: 15
Highway MPG: If I had to guess, I'd say probably around 20.6 MPG.
Combined MPG: 17.8
Fuel Used: 87
Average Highway Cruise Speed: 70 mph
Average Climate: about 85 deg. F in summer, 45 in winter
Mods: j-mod, 3.73 TL, PI intake manifold, 87 and 93 tune, under drive pulleys, Dynomax cat back exhaust, 180 degree t-stat and 1 heat range colder spark plugs, plus what ever else is in my sig.
Mileage on the Engine: 133,300
Comments: No vacuum leaks, EGR is disabled. I normally don't carry a whole lot of weight in the car other than my school books and I. I typically do 50% city and 50% hwy.
 
#234 ·
Yeah... managed high 29 once, low 29 once, then the rest were all 27 or under. Most recently 24-25, then after 3.73s 22ish at best.
 
#235 ·
I was getting 28's and 29's the whole trip depending on who was driving. The 31.5 just happened to be my high. The additives in some gases can mess with fuel economy too. ptschett also claims he had outstanding gas mileage in Nebraska.
 
#236 ·
I've deleted my original post, here's my current set up.

97 Thunderbird
Engine: Modified 4.6 DOHC
City MPG: 13.3-17.1
Highway MPG: 18.2-24.4
Typical mixed mileage: 14.2-16.0, I like to drive the wheels off of it on my days off.
Fuel Used: 91 Octane, Usually from Chevron, Shell, and on rare occasion ARCO (BP)
Average highway speed: 65 - 85.
Average Climate: Hot, Hot, 2 weeks of nice, Cold, 2 weeks of nice, Hot, Hot, repeat
Mechanical Mods: All listed in my 97 Alpine green photo gallery
http://forums.tccoa.com/vbpicgallery.php?do=view&g=144
Milage on the engine: approx 2500 currently.
Milage on chassis:140,500 miles
Rear axle: 8.8 trac-lok 3.27
Average commute: 44 miles round trip for work each day, 4 days a week.
Comments: Not bad, I've considered stepping up to 3.73's though I'm not sure I'll be able to afford driving it around just for fun on my days off if I step up. All mpg calculated for me via scan gauge 2.
 
#237 ·
Engine: 4.6 L
City MPG: 17
Highway MPG: 23
Fuel Used: 87 Octane
Average highway speed: 72
Average Climate: Moderate Winter Hot and Humid summers
Mechanical Mods: Stock
Mileage on the engine: 170k
Comments: Most driving is around town and road trips usually are only a few hours one way.
 
#238 ·
I'm curious. Does 20 mpg sound about right with no EGR and having 3.73's?
 
#239 ·
Probably a little high. When my car was still N/A with 3.73s and functioning EGR, it would knock down 19 mpg highway. Now that is is S/C with 4.10s and no EGR, it gets about 10-12 mpg!
 
#241 ·
1994 Cougar v-8 all stock as far as I know with under 60k miles

city mpg:17
highway mpg:21 at 70mph
average:18-19 mpg

I usually drive slow and easy, so why is the mileage so low? The air filter is ok. The idle seems ok. The copper Motorcraft plugs look good. The fluids seem ok as well.
 
#244 ·
Good tires with good pressure, car tuned up and running good, colder spark plugs, underdrive pullies, synthetic engine, tranny, & differential oils, K&N filter with silencer removed, true-dual exhaust system, no vacuum leaks, cleaned/reconditioned fuel injectors, aftermarket PCM tune, lighten your car as much as possible, drive slower, good 4-wheel alignment, mark viii rear sub-frame & driveshaft, fiberglass hood, smaller torque converter (helps mpg around town), keep car clean & waxed, make sure wheels turn freely with no binding (brakes, bearings, etc), use cruise control, etc, etc.....
 
#245 ·
95 T-bird with 4.6, aod, and 3.08's.....and recomended tire pressure plus 3

My trip to New Jersey, the car was getting 32-35 mpg's at 65 mph average....thas was with no cats, no mufflers, and only 1 of 4 o2 sensors. On the way back, I think I got about the same with dual exhast MadMikeyL sold me from Alicks T-bird (by the way, both the car, my friends, and I love the exhaust) but I was paying more attention to changing road conditions than mpgs. My daily drive to work and back change due to which way I go, highway or back roads, but minimun mpg of 22

I keep fluid up where they need to be, keep oil changed. I should look into my egr system since its starting to throw trouble codes, but thats for my next day off
 
#248 ·
Jeez, the only time my scangauge II says that is after a few miles of coasting after initial start up basically an incorrect reading, how did you pull that off? Were you hypermileing the whole time?
 
#253 · (Edited)
Well, since I put my Fuelly for the Cougar in the 3.8 thread, here's the Fuelly for the Bird. The only continuous set of fuel up data I had available to input was the last quarter of 08. That was before I signed up here and while the car was still stock.



22.8 MPG averaged over 3100 miles; 60% highway. Bests of 29.8, 29.0 and 28.6, all highway.

I'm sure this number will go down once I start driving it this year.

And here is the Mark VIII's:

 
#255 ·
I'd rather use 87 no ethanol, than 89 with ethanol. I get a couple MPG's better, and probably end up saving a dollar or 2, but I pay 10 cents more. Just ranting.
 
#256 ·
Sadly to my knowledge there is no non ethanol stations out here, we also only have 91 for premium instead of 93.
 
#258 ·
We have one station that sells ethanol free gasoline in my area. I live in Virginia Beach, VA and to get this ethanol free gas, I have to drive to Knotts Island, NC. It's a little over an hour long trip. I drove my Mustang down there once as an experiment. I gained 2 MPG with the ethanol free gas. This was with me opening all 4 barrels a couple of times.
 
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