So I just did two 890 mile trips with my 97 4.6 4x4 w/mud tires. Total of 1800 according to my GPS.

Gross weight of truck and loaded trailer (sport bike and car on the trailers) -9300 lbs, 12.5 MPG @ 65 mph with over drive off

Truck with empty - 14.3 mpg @ 75 mph with over drive on

I am so surprised and excited about it. I was get 11.5-10.5 just driving around town. I changed all the plugs and the thermostat right before the trip.

I am going to change out the differential fluid before the next trip.

Got another 900 mile trip next month but it'll be at about 11,500 lbs (total). I'll be happy with 11 mpg.

I love this truck now. I only used it for short commutes in the winter and rainy days the past 18 months I had it. I never even got it past 60 mph before, but now I know the 4.6L can handle quite a bit of load.

 

Are the tires taller than the stock tires? If so, have you changed the speedometer gear? If not, your mileage is off by the % of difference in tire height.

 

The mileage was off of my GPS.

 

14.5! never heard of such a number with mine!

 

i find this hard to believe. Unless you were going downhill both way, with a tailwind. Then, its still hard to believe.

 

I have seen highway averages in my truck (99 5.4L 4x4 sc with 33x12x17 all terrains) of 15.5 on the highway. So I don't see how his empty mpg is impossible. But, I would imagine if I was towing 9300lbs it would be near half that.. So believing you only dropped 2mpg towing almost 5 tons is a bit hard to swallow.

 

Mileage- I've recently changed up my gas brands, and have gotten away from the 10% ethanol blend. My mileage went up a bit from an average of 12.8 city to 13.5 city and highway mileage went up from 16.8 to 18.4 mpg!!!!!
this is in a 2002 4.6l 4x4 ext cab with 285/75-17 tires on it. I also have a tool box in the bed which adds another couple of hundred pounds in it.
I have verified my mileage by calibrating my speedometer with my tuner, and by the local interstate which has the mileage check signs posted and also a conveniently placed police speeding indicator which flashes your speed up on an electric display in a reduced speed zone.
When towing, with about 7000lbs added, my mileage drops down to about 11 mpg or lower range. ICK!

 

The trip was from ohio to louisana and back. I just had rilling hills. Speed up to 80 mph on the down hill to get momentum for the uphills.

The math is pretty easy to do. I only have a masters degree in engineering, but simple enough unless my gps is off. Plus i only had to spend a little above $600 instead of the $900 i was expecting at 9 mpg.

The weight is including the truck.

 

Missed the part where it said gross weight of truck and tow

 

ive gotten 19.5 on the highway with o/d on, tonneau cover, and cruise set and 70 going downhill. same trip up hill best i got was ~15.6 with the same conditions. also only have 265s and 3.73s. maybe possible