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6.7L Power Stroke Engine and Drivetrain Discussion of the 6.7L Power Stroke diesel engine and drivetrain in the 2011-Up Super Duty trucks. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 6.7L Power Stroke engine.

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Old 01-16-2011, 11:03 PM   #1 (permalink)
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Angry losing fuel mileage

I put some new tires on my truck that are only 1 inch taller and about 3/4 inch wider (original 265/70/17) and new tires 285/70/17. Running at 80 psi. I did not think there would be very much difference at all. I lost 5.5 mpg on my drive to Houston on cruise control at 65 mph. Also been losing mpg steadily since the first time I hand-calculated at 21.7 mpg driving 65 on cruise control on the highway steady-state. Last mileage check at right under 11000 miles showed 18.5 hand-calculated with fuel right at edge of fill port. I hand-calculated 13.5 mpg with the new tires. Will take it in to a ford dealer up here to get them to adjust tire size in computer. If that doesn't stop the slide in mileage I am getting rid of this truck. With diesel prices ramping up and no end in sight, I cannot be driving this vehicle if it keeps getting worse and worse mileage like it has been doing.

Any one have any suggestions or experienced this same problem? Truck is box-stock except for ranch-hand bumper replacement on front and the new [very slightly larger] tires. If I knew this was going to happen, I would have: 1) not bought this truck to start with, and 2) would not have put bigger tires on it.

I am extremely disappointed. I think I may trade this truck off before putting many more miles on it. I definitely DO NOT RECOMMEND ANYONE BUYING ONE OF THESE NEW FORD TRUCKS!!!!!!!! Since first check at 3000 miles, it has lost 8.5 mpg.
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Old 01-17-2011, 06:47 AM   #2 (permalink)
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Before you do something rash, get the computer reset for the new tire size, not only is your speedo off, so is your ODOMETER, which will throw off your hand calculated mileage. Also, its winter and as such winter blend diesel is being sold at most stations in the US. Winter blend contiains kero. which has less heat capacity per galon than diesel. Therefore it takes more of it to produce the same amount of work as a gal. of diesel. Also in winter when the truck is cold, the computer employs a cold start strategy that will enrich the mixure for easier starting and warm up, this consumes additional fuel. Further the parasitic losses are higher in cold temps, the tranny, rear/front ends and crankcase oils are thick when cold and take more time to warm up to optimal temps, thus causing increased drag. There may be other things but thes will account for most of your mpg dropoff.
I've driven diesels for better than 20 years and during the winter all of them experienced lower mileage, but returned in the summer.
BTW the tire size increase will have an effect on your overall rear gearing, however slight, that will cause you to use slightly more fuel to accelerate from a dead stop.
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Old 01-17-2011, 07:41 AM   #3 (permalink)
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Scorpio summed it up well.
In the end your tire size may not be that much bigger but your tread most likely is very aggressive and that in itself maybe the problem after its all said and done.
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Old 01-17-2011, 10:42 AM   #4 (permalink)
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Hey hybrids have the same problem Cold air density vs MPG - GreenHybrid - Hybrid Cars

Cold air is denser or thicker, which makes it harder to cut through.

Sometimes a fuel filter change will help if things are a little plugged up. Also do you warm the truck up?
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Old 01-17-2011, 11:50 AM   #5 (permalink)
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I would put the stock tires and front bumper back on and sell what you take off and live with what Ford had in mind. These new vehicles are very hard to self engineer, there not like the old ones.
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Old 01-17-2011, 05:04 PM   #6 (permalink)
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A gas Burner has same problems with gas,in the winter. ethanol blended= lost mpg.

Just let a gas burner warm up as well=Lost mpg

Put bigger tires on=Lost mpg

Why is it a manufacturer spends mega millions $ designing for best economy. and it takes someone a few hundred bucks to mess it all up?
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Old 01-17-2011, 06:15 PM   #7 (permalink)
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Originally Posted by socal2ks View Post
Hey hybrids have the same problem Cold air density vs MPG - GreenHybrid - Hybrid Cars

Cold air is denser or thicker, which makes it harder to cut through.

Sometimes a fuel filter change will help if things are a little plugged up. Also do you warm the truck up?

Interesting article - although he was complaining that he was only getting 49 MPG...
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Old 01-17-2011, 10:15 PM   #8 (permalink)
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You are not going to get 21 mpg consistently out of that truck, If your salesman promised you that kind of mileage, He lied to you. 13-15mpg is very acceptable mileage for 1 ton truck around town.

These trucks are not built for mileage, But to work. If you bought it for a haul the kids to soccer vehicle, You made a mistake and probably should sell it.
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Old 01-17-2011, 11:54 PM   #9 (permalink)
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Originally Posted by commtrd View Post
I put some new tires on my truck that are only 1 inch taller and about 3/4 inch wider (original 265/70/17) and new tires 285/70/17. Running at 80 psi. I did not think there would be very much difference at all. I lost 5.5 mpg on my drive to Houston on cruise control at 65 mph. Also been losing mpg steadily since the first time I hand-calculated at 21.7 mpg driving 65 on cruise control on the highway steady-state. Last mileage check at right under 11000 miles showed 18.5 hand-calculated with fuel right at edge of fill port. I hand-calculated 13.5 mpg with the new tires. Will take it in to a ford dealer up here to get them to adjust tire size in computer. If that doesn't stop the slide in mileage I am getting rid of this truck. With diesel prices ramping up and no end in sight, I cannot be driving this vehicle if it keeps getting worse and worse mileage like it has been doing.

Any one have any suggestions or experienced this same problem? Truck is box-stock except for ranch-hand bumper replacement on front and the new [very slightly larger] tires. If I knew this was going to happen, I would have: 1) not bought this truck to start with, and 2) would not have put bigger tires on it.

I am extremely disappointed. I think I may trade this truck off before putting many more miles on it. I definitely DO NOT RECOMMEND ANYONE BUYING ONE OF THESE NEW FORD TRUCKS!!!!!!!! Since first check at 3000 miles, it has lost 8.5 mpg.

Really? Your disapointed? Did you buy the truck for a daily commuter or a work truck? Daily commuter it will never be economical. You put wider, taller tires on with maybe a softer compound, with winter blend fuel. What do you expect? You don't recomend buying a Ford diesel? What diesel do you recomend? The others are no better with mileage.
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Old 01-18-2011, 03:58 PM   #10 (permalink)
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If you were going with bigger tires the 3.55 gears might have helped keep the mpg steady, but would have been lower to begin with. I agree with whats already on here that most likely other factors are the culprits. These trucks are so heavy and so much power I don't see how a little bigger more aggressive tire would hurt it that much. Also as stated the first run might have been "new truck luck". Even 13.5 mpg isn't bad for a truck with all its capabilities. In comparison most luxury cars don't get much better mpg using premium gas.
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Old 01-18-2011, 08:11 PM   #11 (permalink)
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Originally Posted by Painted Horse View Post
You are not going to get 21 mpg consistently out of that truck, If your salesman promised you that kind of mileage, He lied to you. 13-15mpg is very acceptable mileage for 1 ton truck around town.

These trucks are not built for mileage, But to work. If you bought it for a haul the kids to soccer vehicle, You made a mistake and probably should sell it.
X2

Its a great truck, you can't just Bash Ford for a truck that is used for the WRONG Application. I dont see any 6.7L's racing the LeMans 24hrs.
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