littlevulture

Hello, this is my first post here so please bear with me. I purchased a 2008 FX4 Supercrew in September 2016. Since then I have been tracking my MPG mostly out of curiosity but I have been pretty disappointed with my findings, as the numbers seem low. I've done a fair bit of searching online and the most conclusive "fix" I could find was replacing the fuel filter. I went ahead and replaced both the fuel and air filter and hoped to see at least a slight increase, however, I haven't had much luck. I'll put the specifics of my truck below and along with my recorded MPG, if anyone has some insight it would be greatly appreciated.

2008 F150 Supercrew w/ 6.5' Bed
5.4 V8 w/ 3.73 Gears
Truck has 218000 Miles
Engine and Trannsmission have 60000 Miles (replaced by PO, Remanufactured)
Leveled with 275/70R18 Goodyear Wrangler Duratrac's

I understand that trucks aren't known for their gas mileage, but this on average these seem low to me. When the MPG is around 13-14 that was mostly highway driving, and mostly city driving when it's around 10-12. There is the one entry around 17 and it seems so high relative to the rest I wonder if I made a mistake when I did the math. If I forgot any information that could be helpful please let me know.

BadFish523

Ever had the plugs done? Ever had any timing work done? Does it have the notorious phaser knock? What brands of parts have been used on this truck (oil filter, oil, plugs, timing components)?

littlevulture

To the best of my knowledge the plugs have not been replaced and timing has not been adjusted since the new motor was put in. There is phaser knock, which bothers me, but I didn't think it could be the issue, correct me if I'm wrong. I believe all the components are OEM or OEM equivalent from when the new engine went in, but that was all done with the PO so I'm assuming here. I know the oil was changed right before I bought it, but the brand and weight of the oil are unknown. The oil filter is just a white generic one that says "Product of USA," with some part numbers that don't come up with anything when searched on google. I know this isn't super helpful info but that's all I have right now.

BadFish523

Good info. First get that crap oil filter off there and only use Motorcraft FL820S filters. Next the timing issues absolutely can cause low MPG. I was averaging about 10 to 11 in town before my timing job now Im up to about 12.5 to 13.5 in town. Also the plugs can make a difference in MPGs along with new boots and springs on the coils. Now is the increase in MPGs worth the work? That's not up to me?

littlevulture

Well when I do my first oil change I guess I'll go ahead and replace the plugs and stuff to so I know whats on/in my engine. If that doesn't do it I might go ahead and look into timing and such, I enjoy doing the work so if its doable in a few days it'd be worthwhile as long as parts aren't too expensive. If not I guess I'll just live with the poor MPG's. Thanks for the help!

ReaperHWK

I have a 2006 FX4 and I get the best 13-14 mpg highway. City driving I get around 12 mpg. Sometimes in stoplight to stoplight REAL CITY driving I'll get 9-10mpg.

This seems normal to me for as long as owned the truck from brand new. Remember the FX4's have 3.73's which also affect gas mileage over other F150's(3.42's). Mine also has 20" wheels.

Brian

littlevulture

Well that makes me feel better that you're getting similar numbers to me. It's really been bothering me. Thanks for the info regarding the gears, honestly I thought the 3.73's were standard for all types and trims. With that being said I wonder if it would be possible to run 35 inch tires without hurting the MPG even more. In theory that would drop the final drive ratio closer to a truck with the 3.42's and stock tires so as long as the extra weight and inertia from a larger tire doesn't hurt too much MPG would theoretically go up a bit, or stay the same at the very least.

hahanson

Doesn't seem particularly out of line. Last 6 months 2006 5.4L SuperCrew 4WD:







Aside from all the all common variables (plugs, quality of fuel, oil, air filter, tires, etc), you gotta keep in mind you're pushing well over 6,000 lbs around.

ak_cowboy

Your mileage should be much better. Have you tried disconnecting the battery and resetting the pcm? My 07 with 4.10s and 33s gets 14-15 pretty easily and had a high of 17mpg on the last pure highway run.

fwiw, I have new plugs, synthetic oil, synthetic diff fluid, intake, exhaust, and SCT tuner.

joe mcmillan

Tires are oversize. Has the speedometer been corrected?
If not, your actual miles recorded are less than real.
Other than the above, the winter blend fuels provide lower MPG.
Larger tires are heavier and will lower the mileage.