Anyone have a f 550 with a 7.3L?

Discussion in 'Trucks and Trailers' started by Aaron Marshall, Sep 28, 2008.

  1. Aaron Marshall

    Aaron Marshall LawnSite Member
    Messages: 136

    I have an 01 2wd f550 with a 7.3 automatic. Since I bought it two years ago the best millage I have gotten with it is about 7.4 mpg. Does matter how nice I drive it, doesn't matter if I just drive in town vs. hwy. Air filter is good, it doesn't have a cat. converter, i did put a very mild chip in it, and no change. Fuel filter is new, etc. The only thing I can think that might be bad is the muffler might be pluged up but it seems to have full power? I also have a f350 with a 7.3 and that one will get 16-20mpg depending. There is a large difference in gearing. My f550 has 4.88 gears in it which in my opinion is stupid. I think I might regear it to 3.73s. What kind of millege are you guys getting out of the same truck.
  2. TPendagast

    TPendagast LawnSite Fanatic
    Messages: 11,067

    I have an 02 f450 with those gears!
    The gearing is the problem.
    They dont do any better than the 3.73 gears its not like the 4.88 pull a house out of the ground or anything!

    The 4.88 is a disaster!

    I bet that is your problem, but even with the 4.88 gearing We still dont do that bad on fuel, maybe about 10-11.

    Weve been talking alot about swtich those gears out and honestly we might have done that by now. Ill have to ask the tree manager than runs that truck.
  3. hosejockey2002

    hosejockey2002 LawnSite Bronze Member
    Messages: 1,195

    If you regear your F550 to 3.73 gears (if it is even possible) it will be a total dog and you'll probably wreck your transmission. Having said that, I think something is wrong with your truck getting that low of mileage. I've rented F550 dumps in the past (7.3L diesel with 6-spd manual) and have consistently got 10-11 mpg loaded. Heck, my gas V10 E450 motorhome with 4.63 rear end gears and little tiny 225/75 16 tires gets 7.5-8.5 mpg, and that's moving a combined weight of nearly 17000 lbs.

    Like I said, your mileage is awfully low, but I don't think regearing to 3.73 is going to solve your problem.
  4. Gravel Rat

    Gravel Rat LawnSite Fanatic
    Messages: 9,544

    The tallest gear ratio I would go would be 4:30s any taller than that you might aswell junk the truck it will be useless.

    You buy a F-550 truck what do you expect the mileage of a 4 cylinder.

    Are you sure your calculating your mileage right. My F-450 which weighs 9400lbs empty with a 6.0 6spd I get 11mpg empty and 10 mpg loaded. My previous F-Superduty (OBS F-450) with 4:63 gears 7.3 PSD 5spd weighed 8300lbs use to get 12mpg.

    Where I live there is very little flat roads mostly 8 to 10 percent grades with twists and turns.

    Are you sure your brakes are not dragging and the transmission isn't slipping.

    You should be getting minimum 10 mpg if the truck is running right.
  5. TPendagast

    TPendagast LawnSite Fanatic
    Messages: 11,067

    The 7.3 diesels of the 90s with the 3.73 would get 22 or better on the highway.

    Something happened with emissions that dropped the fuel mileage dramatically after about 2001.

    An 84 naturally aspirated 6.8 ford diesel will get 27 to 28.

    I still think 10 to 11 mph on your diesel something is wrong.
  6. BlackCloudDiesel

    BlackCloudDiesel LawnSite Member
    Messages: 103

    It might be your fuel as well.... I seem to get much better milage with the BP Diesel then anything else. It costs a bit more but if I can get 3 to 4 mpg more on some trucks, I think its worth it.
  7. 02DURAMAX

    02DURAMAX LawnSite Gold Member
    Messages: 3,801

    Now I feel like trying BP Diesel...:cool2:
  8. Aaron Marshall

    Aaron Marshall LawnSite Member
    Messages: 136

    I can regear to a 3.73 gear ration, I just have to also purchase a new carrier for the gear set. I don't know why it would wreck the truck, I just got done driving a f350 drw with 3.73 gears (a 2000) and it got 13-15 mpg hwy. and it had plenty of power.
  9. Aaron Marshall

    Aaron Marshall LawnSite Member
    Messages: 136

    4.30 gears wouldn't be a very significant change in engine rpm.
    no i do not expect to get the millege of a 4cyl but 7 seemed a little low to me sorry for asking
    brakes are not dragging, and the transmition is flawless.
    I would be thrilled to death with getting 10 mpg, thats what I'm hoping to achieve.
  10. Aaron Marshall

    Aaron Marshall LawnSite Member
    Messages: 136

    I have also tried the bp premier diesel and that did nothing for me. I have a friend with a duramax and that seems to make a big difference in that engine but have not had any luck myself. They seem to run slightly better on that fuel though.

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