Why is my fuel mileage less than 8 mpg???

[masospaghetti]

A 5.0/AWD early 2nd gen, like yours, is a relatively inefficient vehicle, even by SUV standards. I think the EPA rates it at 12/17, and you can easily get worse than that if you aren't easy on the accelerator or if you are driving in cold/snowy weather.

That said, 8 mpg is low, although one tank of fuel is a poor sample.

On a related note, at what point should O2 sensors be replaced? I assume at some point they will harm fuel economy even if there's no check engine light being set.

 

[koda2000]

A 5.0/AWD early 2nd gen, like yours, is a relatively inefficient vehicle, even by SUV standards. I think the EPA rates it at 12/17, and you can easily get worse than that if you aren't easy on the accelerator or if you are driving in cold/snowy weather.

That said, 8 mpg is low, although one tank of fuel is a poor sample.

On a related note, at what point should O2 sensors be replaced? I assume at some point they will harm fuel economy even if there's no check engine light being set.

all time best MPG on my 2000 Mountaineer 5.0 AWD is around 22, worst is around 13, which is about 1.5-2 MPG less than my 2WD's. my averages run around 15-16 MPG, but it depends on how/where you drive. if you just leave it idling in your driveway your MPG is zero. 8 MPG doesn't seem impossible if your abusing it.