11-12 mpg 2019 2.7
 

I recently purchased a 2019 Lariat with the 2.7 and only 40k for miles. It has 305/55/R20 Micky Thompson MTs on it and a leveling kit but no other mods. I know that size of a tire will cause the fuel mileage to go down but would it really cause it to drop to a constant 11-12 mpg? It doesn’t matter if I run on the open road with 91 octane in eco mode or around town in regular drive mode. I checked the gas mileage myself as well to compare it with the trucks readout and I also had 12.3 mpg.

I’m just really shocked by this because I had a 2015 XLT with the 2.7 and it had 167k with 33x12.5 MT’s when I traded it off and I never saw below 15mpg with that truck.

Maybe this is a stupid question for asking what am I missing here, but something doesn’t seem right and wondering if anyone has any ideas. Thanks for any input.
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That does sound abnormally low for that particular setup and engine. Hard to tell what the issue might be other than going through a process of elimination for the engine and driveline. Does performance and acceleration feel like it should or you expect it should?

Maybe different gear ratio

performance and acceleration seem normal. Boost doesn’t run abnormal or high on the cluster. It only runs high when the truck needs the rapid acceleration or at the normal times I would expect it like going up large hills sometimes. Doesn’t have excess smoke when I start it or driving it like it’s burning an excess amount of fuel either. No stored codes in the computer. If I hook up my Forscan is there some setting I can look for that maybe someone changed that could have caused this?

filters, throttle body, map sensors. start there. Does seem low for the efficient 2.7

If the speedo hasn't been reprogrammed for the new tire size it will be reading slower which will show fewer miles per tank which will show lower MPG.

^^^^ But he seems to have hand calculated it too. My bet will be on those heavy ass MTs. That will probably be 100lbs+ per corner. A small displacement boosted engine will definitely eat gas to move all that weight around. If you have stock wheel/tire setup, install and I guarantee you pick up at least 3-4mpg without doing anything else. Does the truck have any codes especially for O2 sensors, cats etc? What's the mileage on the highway? How long are your drives when you're checking for mileage?

Even hand calculated if the speedo is off 4-5% that needs to be figured in to the amount.
Stock tires: 500 miles on a tank
New Tires: 475 miles on a tnak.
Granted it's not the full amount but between that and the weight and winter fuel it all adds up.

For reference, my 2020 2.7 came with Hankook Dynapro HT RH12 265/60/R18 110T 34 lbs tires and I changed them to Cooper Discoverer AT3 LT-E 275/65/R18 53 lbs tires. My highway mpg went from about 23 to 21, my all around mpg from about 20 to 18.5, and my ~7000lbs travel trailer towing mpg from 11.5 to 10.5. I drive primarily with 93 octane most of the year except winter when I don't tow. I think, but am not sure, that 87 octane is costing me a mpg or two.

But yes I'd say there is something substantial beyond your 68 lbs 35" tires contributing to your low mpg. One experiment to try is what we do in the towing world with ecoboost, lock out gears and try to target 2250 rpm instead of lowest rpm. Should result in less boost and maybe better fuel economy. If that works then Sport mode or Tow/Haul mode might do you better fuel economy than Eco mode. It sounds counter intuitive but your tires might be well outside the transmission shift points programmed into the truck and tuned for the OEM tires.

Lift the right foot up alittle bit....