I have a 2008 Supercrew F150 4x4 XLT with Goodyear Wrangler Duratrac 285/75r17 and my gas mileage has been horrible lately. I am running mostly highway with some city and I am getting 9-10mpg. My truck has 38,000 miles I have replaced the fuel filter, air filter and ran some fuel cleaner through it with no change in the mileage. I use Valero gas and have tried all three different octanes with the same result. Any suggestions on what I should try next?

 

Running highways with my 2007 SCREW 4x4 XLT, I have clocked 19-20 with no problems. I travel 65-70 most of the time on the highway. City mileage is 14-16 but that drops to 10 if I am pulling my trailer.

I do know that the addition of a Undercover Tonneau cover did NOT add to my MPG although most advertise that it will increase your MPG by 1-2 MPG.......

My suggestions would be to check tire pressure, try using "cruise-control" at a set speed most of the time and finally accelerate slower.

 

yup check tire pressure, accelerate slower and also if you live in the northern part of the US, they use a winter mix gas that will drop your mpgs usually by 2-4mpgs. my 08 reg cab shortbed 4.2L 5 spd with a cold air intake will get between 19.5 and 20 combined in the summer. then winter i get about 15.5mpgs. winter mix gas + tire pressue dropping in cold + 150Lbs of weight in the bed + letting it idle and warm up while brushing it off.

 

They proved on Mythbusters that a truck is designed to get the best gas mileage and air flow at high rates of speed with an open box with the tail gate up. I hate to use Mythbusters as a reference but it was proven.

 

i doubt that. i know they tested the tailgate up theory and the best was no tailgate at all then the tailgate up was 2nd. but they also used a shortbed. didnt test a longbed. also i think my 08 4.2L 5spd gets almost 30mpg driving in 3rd gear at 25-30mph. i live in erie PA where we have a peninsula that is about a 20-25mile round trip. if i cruise it once along with my normal driving i end up getting 21mpg where as without cruising it, i get 19.9 or so. and that is using about a 1/2 tank with both. i am using 2nd and 3rd gear going 25-30mph. but you figure driving an extra 25miles slow like that would not make a 19.9 reading off of 13 gallons go up to 21 on about 14 gallons. but it does. i cruise the peninsula just about every week and always got the same result. at least 1mpg more than just driving normal. i figured it about 10 times last year. best i ever got was 21.2 with the cruising in there. i will have to do it this summer to see if its still doing it. i will post the results i get. thats after the winter mix fuel is gone tho.

 

sorry i think i read your post wrong. you meant "at high rates of speed it is better to have your tailgate up." i took it as mythbusters said it is more efficient for your truck to go 65mph than it is going 35. thats the way i took it. so sorry about that. but along those lines...my 04 heritage's owners manual said that you can save up to 15% fuel by driving 55mph rather than 65mph. but you can get pulled over for going 10mph under the speed limit just as you can get pulled over for 10 over. its dangerous to go too slow in traffic too.

 

I was not stating that higher rates of speed yields better mileage, that concept is just common sense I was just saying that there tests showed that the truck is designed to get the best gas mileage with a tailgate up and an open box...and for a good reason, because that's the way they intended them to be driven. It is definitely a possibility that a cover improves mileage, but from what i have gathered not real likely because they didn't design the truck to get the best mileage with one, I would assume it would screw up air flow just like with the tailgate down and cause extra pressure on the rear of the truck, in turn yielding worse mileage.

 

Results from the show:

"Tailgate down: 5.2 gallons/hr @ 55mph. 1.2 gallons/hr @ 25.
Tailgate up: 5.0 gallons/hr @ 55mph. No reading for 25mph given, but tailgate up was once again confirmed as more efficient.
Hardcover over pickup bed: 5.0 gallons/hr @ 55mph. 1.2 gallons/hr @25mph
Tailgate mesh: 5% more efficient
Tailgate removed: about the same as tailgate up and hardcover
Mesh was most efficient by 5%"

Tailgate up and hardcover were the _same_.

The tailgate up is _not_ the most efficient as you mentioned. The truck is most efficient with the tailgate removed and mesh put in it's place.

 

What?

I've seen elsewhere that a mesh tailgate was one of the worse as it acted like a "parachute" because it didn't create a "bubble" of air in the box for better airflow and didn't allow air to move freely in and out of the bed (like a no tailgate)...

Mythbusters are idiots, BTW.

1. hardcover
2. tailgate up
3. no tailgate
4. mesh

I'll find a link...

 

Check your plugs as well, make sure they are clean.

 

I live in South East Texas so we do not have winter mix gas...I took a trip this weekend running 70mph with it on cruise control I got 15mpg. I am going to check my plugs this afternoon.