I drive a 2000 F-150 ext cad 4x4 auto with the 4.6l v-8. I have a topper and 3.55's in the rear. I purchased this truck in June of this year and enjoyed excellent gas mileage. I was getting between 18.2-18.8 with most of the driving being highway miles. I do drive aprox. 25 miles one way to work.
After my first oil change in late August my mileage went down a little (under 18.0). Then I took a hunting trip to Colorado and returned in late Sept. My gas mileage has dropped drastically since I returned. Also I live in WI. I seem to lose about .5-.75 MPG with each tank. I have questioned 2 dealers, one said the computer has to adjust back to driving in WI. The other said 18 MPG that's great. You should be getting around 15-16. Well my point is that I was getting low 18's and now it's into the 15's. He didn't seem to show any interest and he was the service manager.
My other thought was maybe the cold is affecting the truck already. It's been in the mid 30's and mid 60's so it hasn't been real cold yet. I'm just wondering if anyone has any input on this or has had the same problem. I do tend to baby the truck for the most part. It hardly ever sees 2500 RPM, even with the 4.6l. Could the trip of possiblydone something? It wasn't driven that hard. Thanks for any input.

Travis

 

I had a '97 4x4 ext cab with 4.6, it had orp and 17 wheels. First tank of gas I ran thru it, got 18 mpg, I was in seventh heaven! From then on it was down hill. Had 49000 on it when I traded it, was getting around 15 mpg.. Yes, the cold air affects mpg on these engines--less in winter. I have a '99 f-250 w/ 5.4 (4x4 extended cab) and it gets 13 in summer (no a/c on) and 11-12 in winter.
I stiil feel these are the best all around v8 engines on the road--good luck