is there any reason why i can't seem to get better then 13 mpg recently. I have been keeping track recently cause i thought i was needing fuel quicker then i should have and i am consistantly getting 13 mpg. Now i am running on 35's but i still think i should be getting better then 13 i towed a trailer with a couple of four wheelers up north for the weekend and averaged 15 mpg with the stock tires. I would think that towing a trailer would give you worse mpgs then running 35s but am i wrong.

 

Are you compensating your mileage figures for the parger diameter tires?

Those tires are making you go 15% further than the odometer shows.

Bigger tires do cause your MPG to go down, as well as the type of tire.

 

Wrong... depending on size of the trailer. Goose neck...maybe. Small trailer, no.
Biggest problem with small trailers, IMO, is remembering they are back there.
Because the Cummins won't even feel them.
AND wrong, if you are not correction mileage for oversized tires?? From stock to 35's is about 10% more miles than odometer shows.

EDIT - Opps... 'R-T' beat me to it! MY 10% is from memory so may be 15%??

RJ

 

I gain 1 mpg avg. hand figured when my truck is empty.

With my canopy,tool box and tools my truck weighs around 8600# and I get about 16mpg avg. Stock tires and speedo calibrated with my GPS.
At 67 mph I got my best mileage at 21 mpg with 3.55 gears. This was a non stop run from Ellensburg WA to Missoula MT 4 years ago.

Adding any weight will negatively affect your baseline mileage. Its just simple physics.

You need to: 1. Calibrate your speedo for oversize tires.

2.Recheck your math.

If pulling trailers increased fuel mileage I'd rarely have to fill up!

 

Thats pretty low mileage. I get 22 on the freeway empty, 15-16 city empty. Have yet to tow anything yet...

Agree'd, double check miles

 

how many miles do you have on the injectors and pump? we swapped injectors and pump on a friends truck and he went from 15 mpg to 21 mpg. if the springs in the injectors are worn out then they will open up at a lower pressure not allowing the proper spray pattern.