Fuel Mileage issue?
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Joined: Apr 2012
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Fuel Mileage issue?
Hi guys, been a long time roamer.. decided to register. The thing is, I'm having problems with the truck I just bought, and don't know what else to do. A few weeks ago, I purchased a 1991 F350 7.3L IDI 4x4 Crew Cab, 4.10 rear.. sitting on 36's with dual 5" rear stacks, and 149,000 Miles on the clock.. When I first bought it, I was averaging 7.5 MPG city, and almost 11 MPG highway.. I was distraught, but understood it being a 444 CI it wouldn't get the best mileage.. but now it's terrible. On a 14 mile round trip commute I did yesterday to work and back, my truck managed to get no better than 4 MPG according to my calculations.. If this keeps on I'll have to sell my truck, which would really hurt me since I have an RV I need to pull occasionally, that my quarter ton daily driver would be crushed by. Any ideas?
Fleet Mechanic
Joined: May 2005
Posts: 1,575
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From: Puyallup, WA
Welcome to FTE Ryan, there is a IDI forum where there are a lot of experts a little father down which you might try posting in, or one of the Mods may move this thread to there.
That said, did the PO mod the engine any? Turn up the pump? I assume that you are running 36" tires, not 26" (typo), that and the lift that is required to clear those big tires along with that heavy truck are going to consume a fair bit more fuel to push down the road than a stock setup would. Has the truck been regeared to accomodate those larger tires?
Hopefully the experts will chime in, but i do not see improving mileage that much on a 14 mile trip, after all it may not even be fully warmed up if the PO installed the wrong, or removed althogeth the thermostat. Any ideas on how warm it is running? Especialy with the mods listed. Hopefully for you I will be proven wrong!
Welcome again! David
That said, did the PO mod the engine any? Turn up the pump? I assume that you are running 36" tires, not 26" (typo), that and the lift that is required to clear those big tires along with that heavy truck are going to consume a fair bit more fuel to push down the road than a stock setup would. Has the truck been regeared to accomodate those larger tires?
Hopefully the experts will chime in, but i do not see improving mileage that much on a 14 mile trip, after all it may not even be fully warmed up if the PO installed the wrong, or removed althogeth the thermostat. Any ideas on how warm it is running? Especialy with the mods listed. Hopefully for you I will be proven wrong!
Welcome again! David
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Oops! Sorry typo, 36"'s you're correct. I apologize about the wrong section aswell, I'll be sure to ask for a move. The PO told me he didn't dog the truck, but he did put it to work. As far as the engine, it doesn't have a turbo or anything aftermarket as such, he didn't mess with really anything except for regular maintence, and the tires ofc. It's running straight stacks as I said before, aswell.
Edit: I almost forgot it has a trans cooler added, but that shouldn't do anything to MPG. As far as operating temps, the needle is always low, about half way if I run er' hard.. So around 195-200* F.
Edit: I almost forgot it has a trans cooler added, but that shouldn't do anything to MPG. As far as operating temps, the needle is always low, about half way if I run er' hard.. So around 195-200* F.
FTE Legend
Joined: Jun 2006
Posts: 31,930
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From: Ottawa, Ontario
36" tires are a lot bigger than stock so the speedo needs to be recalibrated so that the odometer is accuarate and thus your milage calculations are accurate. I don't know how you're currently determining milage but you simply cannot use the fuel gauge it's nowhere near accurate. On your truck the speedo is cable driven so all you need to do is change the driven gear on the trans end of it, but first you need to know what color gear you have(you'll have to disconnect it and look) and how much bigger than stock those tires are... the original tire size is on the calibration decal on the drivers door pillar. Then follow the link and scroll down to the appropriate ford section. Speedometer Gear, Ratio Adapter, Speedometer Cable, Speedometer Gears
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