Xplorer

I was tooling around getting a massive 12-14 mpg. Then all of a sudden, which seems to coincide with a swap to mobil 1 oil at 40k, a loss of at least 2 mpgs . I'm lucky if I'm getting 10mpg now. Any clues?

Wrightskis

It's my experience that changing oil wouldn't normally lower your MPG unless you went with a thinker oil. I'm going to assume that you put that same grade and weight as specified by the OEM. I'd look elsewhere such as where you got your gas or whether or not you've changed your driving habits.

Have you noticed any power loss or gain?
Does the engine sound any different?

Franchi

Aye, the oil wouldnt affect that unless you changed the thickness ( and even then it's only a possibility, not a guarantee )

Has the temperature dropped significantly in your area? I know that my truck normally gets about 200 miles to a tank but 175 to 180 in winter. Then again, not exactly cold anywhere in the US yet to affect it that much....

Xplorer

Kept with the 5-20wt oil that supposed to be in it. I got gas from 2 different places & it's been unusually warm here in Pa.

Tmkiowa21

Check out your O2 readings and check the temps.also if you know a guy that does smog he can check the nox reading and tell you if your running rich my be an over fueling issue.my f150 when running well get 15-17 mpg and 320 on a tank

aerosurfer

if you brought it to a shop to get the oil change, re check your tire pressures. they may have set them back to factory reccomended. inflate them back up to max sidewall and you should see an improvement

Tmkiowa21

Just a note Even if you increase the tire psi to max that does not make up for drag it only increases you payload and makes your vehicle ride like a tank.I worked for Goodyear for 5 years in tire development and its not recommended to use max infation unless loads require it

reginhild

I read somehere recently that filling up early in the morning when it is colder you get more actual gas than when filling up in the hotter afternoon. I think it was an EPA report I found online...searching for again.

The above possibility and the fact that different pumps can be off by 5% and still pass inspection in some states makes it hard to measure MPG without filling measuring containers before filling the truck.

Kalenth

I have recently dealt with the same thing, and I think it directly correlates to a lower temp. I also put in 93 octane... instead of unleaded... so I wonder... usually I hear that you get BETTER mileage with super.

JohnD

Has it happened for more than one tank of gas? I have the 4.6 but occasionally i will have a tank or sometimes even 2 in a row where i get much less mileage, then for no reason it seems to go back to normal. I assume its just bad tanks of gas I really dont know what causes it. It has been happening for more than a tank or two I would take it to get looked fat.