21mpg... wtf?
Posting Guru
Joined: Dec 2002
Posts: 1,346
Likes: 4
From: missouri
I would agree with this statement 100%
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
Fair enough. I don't know many of the specifics of the top of my head, but perhaps you can fill some of them in before I can get home and look at the truck. It's an 86 6.9, 4wd. It has a 4 speed manual and I am willing to bet that it has a pretty crazy towing ratio. My tachometer bounces like a jack russell terrier, so I don't really know my rpms, but when I am at 50-55mph on my odometer the engine feels like it's in it's sweet spot... any more and the engine sounds over stretched and I can see some black coming out of the exhaust. I think my speedo goes to about 85, but I'd never take it that high. The engine has about 75,000 on a bottom end rebuild and the truck has about 335,000. I've got some pretty big tires on her, although I doubt the tires are much taller than the factory steel wheels. My Garmin GPS shows me that my speedo is about 5mph off... speedo says 50, I am going 55. I rarely even look at the odometer... only for oil changes. When I figure my efficiency, I either use my gps or figure the exact miles for my route on mapquest or google. To minimize differences in fueling, I use the same fuel pump/nozzle at flying J every fill up. I put it on it's maximum setting and when the nozzle pops, I let the nozzle drip for a few seconds then remove it. Stick it in the auxiliary tank filler and repeat the process. Even if it does foam, I doubt the differences are much more than 1/4 gallon give or take.
OK thats good. if the truck is stock than you can check the door sticker to find out the gear ratio, but by the sounds of it your results were measured as accurately as anyone else's. cruising at 50-55 is the real key here, the stick shift transmission instead of the C6 auto also makes a difference. Have you been able to measure these MPGs consistently over several fillups? say more than 3?
Elder User
Joined: Jan 2008
Posts: 698
Likes: 0
From: Guymon
I think his numbers would be accurate considering the speed he drives. I can get 18 or more at 50 mph but where I usually drive 55 is the minimum speed limit and I would always be impeding traffic so I usually run at least 60 (can get 17.5 mpg there). Before fuel went up, I was doing about 12-13 on the toll road at 85. I just pulled these numbers out of my head as I don't write anything down so I may be like 1 mpg off but I know atleast I can make 18 at 50mph.. I just fill up and try to drive differently for coupple of weeks and change my speed around on the next fuel up.. I know you have a different configruation than mine but just throwing up some info.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
1986 F250 4x4 four speed sitting on 285/75-16 tires with 3.55 gears.
My best this year so far is 12.6975852246 MPG.
I can give that MPG number to you at 15 decimal places if 10 is not accurate enough.
And I think I only hauled one load, about 8500 pounds of Keystone block about 10 miles on that tank of fuel.
My speedo is dead on by both radar and GPS.
I did do 20.4100207058 MPG way back in 2001, but that was back in the days of high sulphur fuel.
My average for the last 11 years, 10.65 MPG.
My best this year so far is 12.6975852246 MPG.
I can give that MPG number to you at 15 decimal places if 10 is not accurate enough.
And I think I only hauled one load, about 8500 pounds of Keystone block about 10 miles on that tank of fuel.
My speedo is dead on by both radar and GPS.
I did do 20.4100207058 MPG way back in 2001, but that was back in the days of high sulphur fuel.
My average for the last 11 years, 10.65 MPG.
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
1986 F250 4x4 four speed sitting on 285/75-16 tires with 3.55 gears.
My best this year so far is 12.6975852246 MPG.
I can give that MPG number to you at 15 decimal places if 10 is not accurate enough.
And I think I only hauled one load, about 8500 pounds of Keystone block about 10 miles on that tank of fuel.
My speedo is dead on by both radar and GPS.
I did do 20.4100207058 MPG way back in 2001, but that was back in the days of high sulphur fuel.
My average for the last 11 years, 10.65 MPG.
My best this year so far is 12.6975852246 MPG.
I can give that MPG number to you at 15 decimal places if 10 is not accurate enough.
And I think I only hauled one load, about 8500 pounds of Keystone block about 10 miles on that tank of fuel.
My speedo is dead on by both radar and GPS.
I did do 20.4100207058 MPG way back in 2001, but that was back in the days of high sulphur fuel.
My average for the last 11 years, 10.65 MPG.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
No, but my average was about 15 instead of 10.
Just filled up again this evening, 265.00.
Fuel has actually come down a little, 4.799 a gallon.
What makes my average look so bad is the winter snow plowing.
I back up so much, I may drive for 10 hours and only show 15 miles on the speedo.
There have been times that I was full when I started plowing and the filled again as soon as I was done.
My MPG was a negative number.
2003 was a bad year, we had a killer snow storm.
I plowed 20 hours a day for 2 weeks.
My MPG average for that year was single digit numbers.
Just filled up again this evening, 265.00.
Fuel has actually come down a little, 4.799 a gallon.
What makes my average look so bad is the winter snow plowing.
I back up so much, I may drive for 10 hours and only show 15 miles on the speedo.
There have been times that I was full when I started plowing and the filled again as soon as I was done.
My MPG was a negative number.
2003 was a bad year, we had a killer snow storm.
I plowed 20 hours a day for 2 weeks.
My MPG average for that year was single digit numbers.
Tuned
Joined: Jul 2004
Posts: 476
Likes: 5
From: Delaware
After new injectors and a used but rebuilt pump my 87 F250 6.9 with 4:10 gears is up to 12mpg from 10mpg. It is a two wheel drive extended cab with a C6. I've got the chance to put in a rear with 3:55 gears, what can I expect for milage with these gears and how bad does the low end performance suffer?
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
After new injectors and a used but rebuilt pump my 87 F250 6.9 with 4:10 gears is up to 12mpg from 10mpg. It is a two wheel drive extended cab with a C6. I've got the chance to put in a rear with 3:55 gears, what can I expect for milage with these gears and how bad does the low end performance suffer?
3.55 gears will help on the freeway, but you might find that around 40-50 MPH on steep grades that the engine will bog down more than before when it had 4.10 gears. For starting off the line, you are going to loose some, but not very much. Above 15 MPH it will feel the same, below 15, it will feel only slightly different.
With 3.08 gears the differnece felt more like gaining an extra top gear at the expence of a low range 1st gear. What was neat about my swap is that I gained the ability to drop to 2nd gear on steep grades below 55 MPH. This gave me the ability to pull just as hard but still be able to cruise well at higher speed.
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Tuned
Joined: Jul 2004
Posts: 476
Likes: 5
From: Delaware
Here in Delaware we have flat ground but if I have to run up to PA. I've got hills to deal with. Usually the load is in the truck as in firewood or an engine or something. I do pull a trailer with a car on it. I'm obviously looking for better fuel economy as 10-12 mpg at almost $5 a gallon just doesn't cut it. I just wanted to figure out if the change to 3:55's was worth it mileage wise.
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