Mpg sweet spot
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Cross-Country
Joined: Dec 2016
Posts: 82
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Mpg sweet spot
Seems to me that when on the highway the sweet spot for the super duty 7.3L for getting good gas mileage is at 70mph. It was the same way in my f250 6.2l. Does anyone else notice this?
Hotshot
Joined: Jun 2003
Posts: 12,361
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From: SW VA
I didn't buy my truck to worry about gas mileage. That said, these things have the aerodynamics of a brick on stilts. You will get better fuel mileage by slowing down. If you think 70mph is the "sweet spot", you should try 60mph...
Logistics Pro
Joined: Jan 2010
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Newer trucks with better gears will get better mileage. But with the crappy aerodynamics, higher speeds will reduce it, because resistance due to frontal area increase as the square of speed - it's not a linear formula.
Logistics Pro
Joined: May 2022
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From: Everywhere and nowhere
This is completely subjective by tire size, axle ratio and speed. My DRW with 31.5" tires and 4.30s would get over 20mpg at 45mph. I put 33s on it so now I get worse mileage except around 50mph I can get around 20mpg.
I would not say 70mph is a sweet spot for mpg with any tire size and gear ratio.
I would not say 70mph is a sweet spot for mpg with any tire size and gear ratio.
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From: Itinerant
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Cargo Master
Joined: Apr 2018
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My dad used to tell me it was at peak torque and top gear would be your best mileage, I don't know if that's true or not.
Fuel is actually free for me, in the majority of our work is T&M, so let it burn.
Unless you're in California, or worse off Nevada after the beginning of next year. You won't have it to burn.
Fuel is actually free for me, in the majority of our work is T&M, so let it burn.
Unless you're in California, or worse off Nevada after the beginning of next year. You won't have it to burn.
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Cargo Master
Joined: Aug 2012
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From: Kaufman TX
My dad used to tell me it was at peak torque and top gear would be your best mileage, I don't know if that's true or not.
Fuel is actually free for me, in the majority of our work is T&M, so let it burn.
Unless you're in California, or worse off Nevada after the beginning of next year. You won't have it to burn.
Fuel is actually free for me, in the majority of our work is T&M, so let it burn.
Unless you're in California, or worse off Nevada after the beginning of next year. You won't have it to burn.
As far as peak mileage goes, slowing down will get you better mileage. Though the efficiency relationship between power and fuel consumption is related to torque, mileage is a function of power demand not torque. Vehicle drag increases by the speed squared so it really adds up at highway speeds so slowing down a little bit reduces power required a lot. Generally you'll get best mileage going as slow as you reasonably can in top gear. Where your dad was real close is the published peak torque values is at WOT, but as you reduce throttle the RPM of peak torque drops too. At 5% throttle the peak torque RPM will be a lot lower than at WOT. In top gear that goes hand in hand with slowing down. So if you are in top gear, and going as slow as reasonable (varies but probably about 50-55 mph) then you'll be right around peak torque for your lower throttle input and getting the best mileage.
Laughing Gas
Joined: Sep 2017
Posts: 1,144
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From: Southwestern Pa.
And FWIW, I found that my '17 6.2L, 6R100 didn't get it's best mileage until the trans was warmed up to it's normal operating temp, which was close to 200F. That took a good 20-25 minutes of driving time. My '25 7.3L, 10R100 seems to be the same...taking at least as long as the '17 did to warm up to it's best op temp.
Logistics Pro
Joined: Jan 2010
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And FWIW, I found that my '17 6.2L, 6R100 didn't get it's best mileage until the trans was warmed up to it's normal operating temp, which was close to 200F. That took a good 20-25 minutes of driving time. My '25 7.3L, 10R100 seems to be the same...taking at least as long as the '17 did to warm up to it's best op temp.
Laughing Gas
Joined: Feb 2020
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From: End of the Rockies
Big improvement over the Triton series.
Cargo Master
Joined: Apr 2021
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From: NW Wyoming USA
It seems pretty simple to me.
The lowest speed you can stay in the highest gear is going to give you the highest mpg.
My 7.3 4.30 34.5” MTs 2” air deflector at 65 mph gets 14.4 mpg, at 70 mph it gets 12 mph.
The posted speed limit around here on these two lane highways is 70, so that’s the speed I go. When I’m on four lane highways I go 65 mph.
The lowest speed you can stay in the highest gear is going to give you the highest mpg.
My 7.3 4.30 34.5” MTs 2” air deflector at 65 mph gets 14.4 mpg, at 70 mph it gets 12 mph.
The posted speed limit around here on these two lane highways is 70, so that’s the speed I go. When I’m on four lane highways I go 65 mph.
Last edited by GAZZILLA; Dec 17, 2025 at 10:31 AM.
Logistics Pro
Joined: Jan 2010
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It seems pretty simple to me.
The lowest speed you can stay in the highest gear is going to give you the highest mpg.
My 7.3 4.30 34.5” MTs 2” air deflector at 65 mph gets 14.4 mpg, at 70 mph it gets 12 mph.
The posted speed limit around here on these two lane highways is 70, so that’s the speed I go. When I’m on four lane highways I go 65 mph.
The lowest speed you can stay in the highest gear is going to give you the highest mpg.
My 7.3 4.30 34.5” MTs 2” air deflector at 65 mph gets 14.4 mpg, at 70 mph it gets 12 mph.
The posted speed limit around here on these two lane highways is 70, so that’s the speed I go. When I’m on four lane highways I go 65 mph.