I have a 99 f-350 4x4 dually diesel (7.3 powerstroke). Lately driving down the interstate not pulling anything at like 70 mph. I only get 12-13 mpg? Is this normal? How many gears does my tranny have?

If you have any ideas let me know please!

thanks

 

I'd say your MPG is in the normal range. A 4R100 is a 4 speed.

 

Try doing your mpg again while driving about 60 mph. It seems like when your engine goes over 2000 rpm on the 7.3 mileage really suffers.

 

do you have like a speed vs rpm ratio thing so i know if my tranny is shifting right?

 

i would believe that 12 mpg with an automatic at 70 mph is pretty normal for a 7.3.

i get about 17 with mine when i keep it at 60 mph, at 70 mph i can watch the needle move on the fuel gauge

 

I have a six speed so I have no clue about the auto shift points. Like X1 said, there's a big difference in mileage from 60-70 mph. I made several long trips from North Missouri to Dallas when my truck was much newer and figured that out pretty quick. That was back before the ULS fuel too.

 

My 7.3 was happiest at 1850 rpms which put me at 65-68 mph depending on conditions. I had 4.30 gears in my Excursion. The general rule of thumb is anything over 2k the 7.3 gets thirsty.

On flat highway I got an avg 16 mpg doing 65 with no cruise.

 

My 3.73 geared 7.3 X cruises right around 2000-2100 rpm at 70mph.

I only get 13-14mpg pulling all the trailers in my sig at 65ish mph.

 

how in the world did you do 65-68 with 4.30's at 1850 rpm?

my pumpkin tag says i have 4.10's and i am doing 2000rpm at 65

 

It's really mainly an estimate, I didn't have a gps or anything to verify the "actual speed". I was told by the PO there was 4.30's in it but maybe I trust others too easily. The tag on the pumpkin rusted away after the years and I never gave it much thought until now but with the shady history it's possible it was just the standard 3 73. After 306,000 miles anythings possible!