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Great highway mileage, terrible city mileage

708 Views 16 Replies 6 Participants Last post by  SantaCruzer
Hi everyone, I'm a new owner, just getting to know a 2021 super crew longbox I bought with 21k miles on it. It's a 3.31 gear ratio with 32x10.8 r18 geolander A/T on stock aluminum rims.

My first highway test was a wonderful feeling, ending with a dash reading of 30 mpg 馃榿

City mileage has been a much different story. 10.5 mpg 馃槥

I live in a mountain town so we've got steep grades. I'm not driving wide open or anything but the ascent home is about 3-4 minutes straight up hill. I did a 12 mile test in 3-4 separate trips of roughly the same routes, 70% downhill/flat and 30% hills. All between 18-30 mph.

-Drive mode is in 'Normal', 2H.
-I checked to see if it was in regen today while idling with Forscan Lite and it doesn't appear to be (EGT 11-14 are all in the 180-210 range, DPF_REGEN says 'Inactive').
-Wheels are all spinning freely

Is there something else for me to check out or is this just a bad gear ratio for my city?

Apart from this, I'm loving the truck. A much welcome change from years of 90's 4x4s. Nicest vehicle I've ever got to drive!
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I break 30MPG at 70MPH on relatively level highways. I have a 2021 Lariat Supercrew with short box. Around town is low 20's. I go up and down moderate hills, but I don't live in a mountain town. Even so, I think something is wrong if you're only getting 10.5 MPG.

Is that on the display, or actual measured by miles on the odometer and gallons in the tank? If not, do that measurement. Display is often off by more than 10%.
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As Pete says don't fully rely on the display, do your own measurement. Also have the fuel filters been changed yet? Some have reported the filters look bad at 20k. This engine uses very high pressure on the injectors and the returned fuel seems to contaminate the filter.

My truck lives in the city, few long hauls but I am a flatlander.
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I too live in the mountains but of northern NH. Its rural closest stop light is 60 miles away. On the highway 70mph >30mpg. Around "my town"28.1 mpg was the worst I ever got. Alot of 4wd in the winter. On a road trip to SW Florida hauling a steel trailer and a 4000 lb load 65-75mph 19.1mpg. In Florida avg 29mpg AC on . I have 3.55 gears. I always drive in Eco mode , keep my foot out of it . Plenty of stop signs and traffic lights but I still consider it mixed driving not true city. Bone stock motor no mods or tunes. Love the truck.
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Thanks for the input, guys. Yes this is the dash reading. Either way, 10% would be 2-3 mpg, whereas it sounds like I'm seeing a 10-15 mpg difference for city.

I have fuel filters ready to go on-- My thought was that I would get through the tank that came with the truck as it's a bit old, fill up with summer diesel and then I'll do the hand calculation as well. Won't take long if the city mileage keeps this rate!
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The fuel filter would not change the fuel consumption, only limit the top end power. Something else is going on. Measure your actual fuel consumption, then post back here.
There are some simple things that you can do like checking to see that your grille shutters are closed when the truck is cold and ensuring that your coolant temperature is coming up to operating temperature in time. The 18 - 30 mph is really slow, so I wonder if the truck is warming up even with the grille shutters closed and the thermostat working properly.

The other thing that I am wondering about are the tires you are using. I have no idea how a 32x10.8 tire compares to a 265R65-18, but I suspect it may be larger and heavier. If the diameter is different, it is similar to gear ratio change that is not programmed into the ECU. Also, if that was not corrected for by coding, your odometer and speedometer will be inaccurate and hence your MPG will not be correct. You would need to do hand calculations with a GPS-based odometer (or make sure your speedometer is corrected for these tires).

As for tire weight, I sometimes listen to these auto technicians banter as background noise when I work in my garage. The one technician at the 13 minute mark made a comment about the fuel economy impact of heavier tires in a 3.0 F-150 that made my ears perk up. It's all hearsay, but an interesting data point nevertheless.
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There are some simple things that you can do like checking to see that your grille shutters are closed when the truck is cold and ensuring that your coolant temperature is coming up to operating temperature in time. The 18 - 30 mph is really slow, so I wonder if the truck is warming up even with the grille shutters closed and the thermostat working properly.

The other thing that I am wondering about are the tires you are using. I have no idea how a 32x10.8 tire compares to a 265R65-18, but I suspect it may be larger and heavier. If the diameter is different, it is similar to gear ratio change that is not programmed into the ECU. Also, if that was not corrected for by coding, your odometer and speedometer will be inaccurate and hence your MPG will not be correct. You would need to do hand calculations with a GPS-based odometer (or make sure your speedometer is corrected for these tires).

As for tire weight, I sometimes listen to these auto technicians banter as background noise when I work in my garage. The one technician at the 13 minute mark made a comment about the fuel economy impact of heavier tires in a 3.0 F-150 that made my ears perk up. It's all hearsay, but an interesting data point nevertheless.
Thanks for the suggestions. I'll check the shutters. These are fairly short trips between 5-15 minutes of driving time per trip. Maybe this is the cause....I'll reset the trip mileage and add some drive time to see if driving warm changes things.

Right, tires. I should mention that they're the stock size that came with this truck - 275/65r18. I don't know that they were Geolanders, as the window sticker just says 'OWL All terrain'.
The fuel filter would not change the fuel consumption, only limit the top end power. Something else is going on. Measure your actual fuel consumption, then post back here.
I still have 3/4 of a tank so it will be a while until that happens. Will do though.
Don't expect miracles with the summer fuel versus winter blend. #1 diesel has 10% less energy than #2. I live in a rare part of the country where we run 100% #1 diesel for almost 5 months/year; most places are 60/40 or maybe 80/20 #2 to #1. Combined with winter tires, I get a 10% reduction in fuel consumption during the winter. Since you are driving short distances; however, warm-up time in cold versus warm weather may play a role. My truck rarely drives less than 150 miles after it gets started, so warm-up time is insignificant. That said, even under load (65-70 mph), I noticed that I don't get up to operating temperature until I've driven 3 - 4 miles. You might want to see what sort of difference you get running the same route fully warmed up.
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Don't expect miracles with the summer fuel versus winter blend. #1 diesel has 10% less energy than #2. I live in a rare part of the country where we run 100% #1 diesel for almost 5 months/year; most places are 60/40 or maybe 80/20 #2 to #1. Combined with winter tires, I get a 10% reduction in fuel consumption during the winter. Since you are driving short distances; however, warm-up time in cold versus warm weather may play a role. My truck rarely drives less than 150 miles after it gets started, so warm-up time is insignificant. That said, even under load (65-70 mph), I noticed that I don't get up to operating temperature until I've driven 3 - 4 miles. You might want to see what sort of difference you get running the same route fully warmed up.
So nothing substantial then. I think you called it correctly with the operating temp. I just went for an hour long city driving test- 14 miles in the flat/minor hilly areas of town and got 18.3 mpg from the dash. 15 minutes of that was getting to operating temperature.

At the hour mark, I used Trip 2 to find the mpg I'm getting from the base of the mountain all the way home (turns out it's 1 mile taking 4 minutes at 25-35 mph) and it came in at 9.3 mpg :rolleyes: The drive up the hill took the overall 18.3 mpg down to 17. So I think that's it then. Truck hasn't been warm enough and I'm doing too many quick trips where that 9.3 mpg (probably worse cold!) is around 40-50% of the drive.

So fuel economy seems great for highway and some types of city driving. Thanks for the help everyone, it's much appreciated.
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I second the fuel filters....I switched tire types but kept same size......my city mileage went way down....I leveled and it went down again..... you lifted or leveled ? still 30mpg on HWY...it just seems that around town it takes more energy to get moving with level and more A/T style tread...have fun!
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I second the fuel filters....I switched tire types but kept same size......my city mileage went way down....I leveled and it went down again..... you lifted or leveled ? still 30mpg on HWY...it just seems that around town it takes more energy to get moving with level and more A/T style tread...have fun!
Nope, everything is stock right now. I have 34.3x11.8 r18 (295/70r18) Ko2s waiting to go on. 70 lbs a piece....The Geolanders on there now are 43. The weight affects things for sure, as well as a reduction in gearing ratio in my case will go from 3.31 to 3.10. Hopefully on flat highway the new ratio will help offset the mpg eaten up by the heavier tire setup. I'll report back on how it is around the city 馃槵
For what it's worth, I had to run up a local hill (1.5 miles, 10% grade) and decided to see what my trip computer read. At about 35 - 38 mph running between 6th and 8th gear (3.55 ratio), my mileage read 15.0 mpg over this very short, very unscientific test. The truck was fully warmed up.
For what it's worth, I had to run up a local hill (1.5 miles, 10% grade) and decided to see what my trip computer read. At about 35 - 38 mph running between 6th and 8th gear (3.55 ratio), my mileage read 15.0 mpg over this very short, very unscientific test. The truck was fully warmed up.
Haha, unscientific is the name of my game here. But a ballpark figure is nice to have. I'll check what gears I'm in next time. How did you get the grade, do our trucks show that? (I haven't used the offroad screen yet). Are you on the stock 265R65-18?
I am not aware of a place where the F-150 shows grade; this particular hill has a big yellow sign with the grade posted. The truck is running winter tires in stock size (275/55 R 20) and I still have winter fuel in the truck. I plan to swap to my 275/65 R-18 summer tires and wheels this weekend, but my trip computer says I still have 840 miles on (winter) fuel left.
I am not aware of a place where the F-150 shows grade; this particular hill has a big yellow sign with the grade posted. The truck is running winter tires in stock size (275/55 R 20) and I still have winter fuel in the truck. I plan to swap to my 275/65 R-18 summer tires and wheels this weekend, but my trip computer says I still have 840 miles on (winter) fuel left.
So the same tire size then...with winter being softer but the A/T probably being heavier. Thanks for testing that out, quite the discrepancy but so many different factors to consider.

Now I'm at 150 miles of mixed driving and my onboard mileage says average 23 mpg. I think I can live with that 馃榿
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