# terrible millege on my f550



## amars415 (Nov 29, 2006)

I've got a 01 f 550 7.3l auto 2wd and I get between 6 and 7 mpg. IMO the gears are too low 4.88. It never runs in its peak torque rpm range, always reving too high. The tranny seems fine, no cat. converter, air filter good, new fuel filter, etc. This is what its been since Ive owned the truck, I would be thrilled to death with 10-12 mpg, what are you guys getting in your f550s with 7.3? any suggestions? I"ve already got it mildly chiped and no help. Thinking of re-gearing. thanks!


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## JohnnyRoyale (Jun 18, 2006)

Everything improved when I superchipped mine, and added K&N air filter. Its worth a try.


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## 04superduty (Jan 9, 2004)

dont do a K&N sway on your truck, at least with diesels they are not recommended since they let to much junk thru.


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## musclecarboy (Aug 19, 2007)

The 550's/5500's usually have 488's I'm pretty sure.

How long have you had the truck? Has it always been like this? Odd to see under 10 on a 7.3.... maybe a new 6.4.


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## Jay brown (Dec 26, 2005)

that sounds about right for fuel mileage.... our 2000 model redlines at about 80 mph with the 4.88's.... it's nice to have the low gears though when your towing heavy... keep her at about 45 mph....lol


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## Doakster (Aug 15, 2008)

JohnnyRoyale;593261 said:


> Everything improved when I superchipped mine, and added K&N air filter. Its worth a try.


  A no no to add on the 7.3


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## Doakster (Aug 15, 2008)

amars415;593251 said:


> I've got a 01 f 550 7.3l auto 2wd and I get between 6 and 7 mpg. IMO the gears are too low 4.88. It never runs in its peak torque rpm range, always reving too high. The tranny seems fine, no cat. converter, air filter good, new fuel filter, etc. This is what its been since Ive owned the truck, I would be thrilled to death with 10-12 mpg, what are you guys getting in your f550s with 7.3? any suggestions? I"ve already got it mildly chiped and no help. Thinking of re-gearing. thanks!


Has the truck always run well for you, any white/black smoke etc?


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## JohnnyRoyale (Jun 18, 2006)

Doakster;593915 said:


> A no no to add on the 7.3


Thats the first I heard. Why?


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## Doakster (Aug 15, 2008)

JohnnyRoyale;593925 said:


> Thats the first I heard. Why?


There are much better tuners out there than superchips that will make you're truck run better with lower egts, and the K&N is widely know for lack of filtration and making you're compressor wheel on your turbo look like someone put sand paper to it. But that's all for another topic/thread.


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## TEX (Nov 24, 2003)

i would say its the 4.88's yes they are nice for towing and pulling around town but at high way speeds WOW. a lot of our fire trucks are F550 with the 4.88s and they get nothing for mpg. even a regear to a 4.30 something would help. i guess it comes down to where do you do most of your driving miles, hiway or in town?


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## amars415 (Nov 29, 2006)

Doakster;593916 said:


> Has the truck always run well for you, any white/black smoke etc?


I've had it since Dec of 06 and it has always run very well, no smoke, etc. And since I have owned it, I have had the same fuel economy.


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## amars415 (Nov 29, 2006)

I am thinking of re-gearing to a 3.73 maximum and I think a 4.10 minimum. I just got done driving an f350 drw with 3.73's and it had plenty of power pulling a load. Right now with the 4.88 going 55mph, I will slow down going up hills (fully loaded) because in my opinion, the engine doesn't have any torque at that rpm. And for those that are going to say that 3.73 are to high, just remember that alot of dodge drw trucks run with 3.55's, granted they have a lower torque rpm and I would never go that low on a 7.3 unless it was a commuter truck.

engine rpm with stock gears @ 70mph: 2800 (redline @ 3200)
engine rpm with 4.30 gears @ 70mph: 2467
engine rpm with 4.10 gears @ 70mph:2352
engine rpm with 3.91 gears @ 70mph:2243
engine rpm with 3.73 gears @ 70mph:2140


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## amars415 (Nov 29, 2006)

TEX;594351 said:


> i would say its the 4.88's yes they are nice for towing and pulling around town but at high way speeds WOW. a lot of our fire trucks are F550 with the 4.88s and they get nothing for mpg. even a regear to a 4.30 something would help. i guess it comes down to where do you do most of your driving miles, hiway or in town?


most of my miles are in town and only a few times do I have to go more than a half hour drive even, but when they are longer drives I can watch that needle drop fast! You would think that it would get good millege in town because it doesn't have to work very hard to get rolling, but it doesn't matter if i'm in town or on the hwy.


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## 04superduty (Jan 9, 2004)

have you looked into a gear vendor over drive unit? that way you keep your low gears for getting a heavy load moving, then have the higher ones for cruising.


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## amars415 (Nov 29, 2006)

yeah, i looked at gear vendors but its like 3000 dollars, i can buy alot of diesel for that much money and I could change the gears in the rear end 3 times. I really don't think i'm going to have a lack of power with 4.10 or 3.73 gears, i think with 4.88s you have so much unusable power anyways. literally, i could pull over a house... but there is no way to get enough traction for all that power.


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## ducatirider944 (Feb 25, 2008)

amars415;596159 said:


> yeah, i looked at gear vendors but its like 3000 dollars, i can buy alot of diesel for that much money and I could change the gears in the rear end 3 times. I really don't think i'm going to have a lack of power with 4.10 or 3.73 gears, i think with 4.88s you have so much unusable power anyways. literally, i could pull over a house... but there is no way to get enough traction for all that power.


3K is cheap that is only 750 gallons @ $4.00 a gallon. So if you jumped your milage to say 10-11 mpg or a 4 mpg increase that would only be 11500 miles at 6 mpg to 10 mpg or 13000 miles at 7 mpg to 11 mpg. After that it will be money in the bank. I bet an overdrive will cost more than 3K. I bet you would spend 1K just changing the rear ratio if you have it done by someone, 2K if it is a 4x4 truck. 4.10 would be a good combo ratio in my opionion


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## Jay brown (Dec 26, 2005)

we're grossing 39K with ours and the 4.88 is the perfect gear for the job, that's why i bought the truck....... really if ya think about it, a 550/5500 is designed for hauling and pullling, not for fuel conservation....i'd save the $3k on the gears and buy an old 2wd toyota and use it when your not pulling/hauling


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## bribrius (May 5, 2007)

put taller tires on it.


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## Jay brown (Dec 26, 2005)

22.5's might fit..


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