My 08SD Crew Cab Short box has a the V10 with 4:10 rear. I have 315's riding on stock rims. The truck runs like a dream. Rides like a dream. Beautiful.
I avg 7.1MPG. All the time! I've seen 7.8

My buddies with an 03 and a 05 both with V10's see 10.

Do you think I have somethinggoing on with my engine for that low of a
Mpg number?

Opinions?

 

Truck in sig,

I'll average between 10- 11.5 MPG depending on conditions. Pulling 5th wheel 7.5-8 mpg all the time.

Your mileage does seem to be low.

 

Very low for sure. Iv heard of guys getting 7 but theyre usually ALWAYS towing something... Maybe you've spit a spark plug or two and running on fewer cylinders? Just a guess lol. Itd be worth looking into

 

Are your friends trucks on 35s as well? If not then that's a contributing factor.

I would also check how you drive. I know my truck was getting 9mpg with the 5.4 changed the plugs and got 10. Changed how I drove and an now getting between 11-14 depending on where.

Transmission and oil temp also affect this. Because its just getting to be winter I don't think this has as much of a bearing, but on my commute its only 16 miles. Once the temperature drops below 40° my transmission doesn't even come close to hitting operating temp, and I can see a mpg difference between the early mornings when it's 15° and afternoons when its 50°

 

When going with larger tires, it is critical to get your speedometer recalibrated. This alone alone could be your issue. Bigger tires withouth calibrated speedometer means you are going faster than you speedometer reads, and traveling farther than your odometer records. Both would mean "lower" fuel economy.

 

+1 And I have a hunch the truck didn't come from the factory with 315's so that would throw it off

 

No truck did not come from the factory with 315's.
I haven't spit any plugs either.

 

i you didn't re-calibrate yo are really getting close to 8-9 mpg if that makes you feel any better lol

 

Hate to say it, but I think those big meats combined with your driving style are the culprit. Don't feel bad though, my Excursion with stock tires and 4.30s never exceeded 12 MPGs on the highway.

 

I am
Being totally honest. I do not go heavy on the gas pedal.

 

So who or what is involved in a recalibration of my speedo?

 

You would need to buy a tuner

 

Ok. What is the tuner I should buy?

What would this do for me?
I'd hate to spend a lot of money and only use it once to calibrate for larger tires.

 

Being you have an 08 there is much more that can be done with your truck. It can modify trans patterns and pressure for a better transmission feel, it is I believe much more effective at getting power out of the motor it self and you would be able to recalibrate the speedo to larger tires.

 

Anyone in Illinois do this !???