Ford F-250 & Ford F-350 The heavier duty full sized trucks from Ford, offering bigger, more powerful engines and drivetrains for the abuse they may go through in the workplace.

New '05 F-350: unexpectedly low mileage

Old 09-16-2005, 03:40 PM
Thread Starter
Join Date: Sep 2005
Posts: 1
Default New '05 F-350: unexpectedly low mileage

Hi all,

NB: First post, go easy on me.

I just bought a brand new '05 F-350 4x4 6.0L Power Stroke turbo diesel, single rear wheel, with expectations of fuel economy around 15 MPG city, 20 MPG highway after speaking with several people before my purchase about mileage. I love the truck and have almost 4000 miles on it, but I only get around 12 MPG city and 15-16 MPG highway with no load.

I've spoken to other new F-350 owners as I've come across them and asked about their mileage. Those with aftermarket exhaust and/or chips get much better mileage. One guy with the exact same truck, all the way down to the trim level (King Ranch), is easily getting 15 MPG city/20+ MPG highway with a larger exhaust system, unpacked catalytic converter, and aftermarket chip.

So I have a few questions:

* Are the exhaust system & chip the only things that can improve mileage? What are the biggest contributors to fuel economy?
* I've been told that simply installing a larger exhaust system will be effective in substantially increasing mileage. How true is this?
* Is there anything I can do to the intake system to improve mileage?
* How does altering the exhaust system affect my warranty?
* How does altering the computer chip affect my warranty?
* How does unpacking the catalytic converter affect my warranty? How does it affect my emissions control system? Will it cause me to fail emissions inspection the next time they check (WA state)?

I'm sure that these questions will lead to others, so I'll leave this list of questions as it is. Thanks in advance for your help.

Old 09-16-2005, 05:02 PM
Join Date: Jan 2005
Posts: 735
Default RE: New '05 F-350: unexpectedly low mileage

I'd expect that your gas milage will impove as it is broken in. As for the ?'s I think amy mod will void warrenty, and I wouldn't alter any cat. maybe change to larger one but not alter it.
Old 09-16-2005, 06:07 PM
Join Date: Aug 2005
Posts: 96
Default RE: New '05 F-350: unexpectedly low mileage

also adding in an aftermarket air filter (fram air hog or K&N) will also help increase your mileage w/o voiding the warranty
Old 09-16-2005, 07:29 PM
Join Date: Jun 2005
Posts: 59
Default RE: New '05 F-350: unexpectedly low mileage

Do not change the air filter on your diesel. For those of you that have not seen it, it is the biggest and best air filter system that Ford has ever put on the Super Duty. It will last and last and does not leak if you don't mess with it. It is very hard to remove and install by the way it is designed so do not let the guys at the quick lube take it out to inspect it. I have seen plenty not put back together correctly and injesting dirt into the engine after the lube guys had a hand at it. It has a filter minder on it that you can monitor and it will also turn the light on in the dash if it gets to restricted.
Old 09-17-2005, 01:26 PM
Join Date: May 2005
Posts: 298
Default RE: New '05 F-350: unexpectedly low mileage

you are driving a f350 if you wanted better fuel mileage you should of bought a smaller truck lol! but you should not follow others with chips and modifications if you want your warranty, ford doesnt like modifications
Old 12-27-2005, 02:01 PM
Join Date: Dec 2005
Posts: 1
Default RE: New '05 F-350: unexpectedly low mileage

US Code - Title 15, Chapter 50, Sections 2301-2312

Legally, a vehicle manufacturer cannot void the warranty on a vehicle due to an aftermarket part unless they can prove that the aftermarket part caused or contributed to the failure in the vehicle (per the Magnuson Moss Warranty Act (15 U.S.C. 2302(C)) . For best results, consider working with performance-oriented dealerships with a proven history of working with customers. If your vehicle manufacturer fails to honor emission/warranty claims, contact EPA at (202) 260-2080 or If federal warranty protection is denied, contact the FTC at (202) 326-3128 or For additional information, check out the following links:

you can read the full article here
Old 12-31-2005, 10:34 AM
Join Date: Apr 2005
Posts: 9
Default RE: New '05 F-350: unexpectedly low mileage

Want fuel economy? Do like everyone else BUY a cummins till FORD puts in a I-6 cyl!!!!![:-][:-][:-]
Old 01-02-2006, 04:43 PM
Join Date: Dec 2005
Location: Texas
Posts: 30
Default RE: New '05 F-350: unexpectedly low mileage

I have a 99 F-250 4x4 Crew Cab w/ a 7.3L diesel. For the most part I think I am getting around 12.5mpg. Hard to tell because of the bigger wheels and tires. Anywho, about the mod's. There is a law that protects individuals as far a modifications go. On the other hand, if something goes wrong, they have to prove the mod caused the problem. I think it is pretty much a crap shoot.
Old 01-14-2006, 09:43 PM
Join Date: Dec 2005
Posts: 158
Default RE: New '05 F-350: unexpectedly low mileage

As was stated before, keep the stock style filter setup. The only thing better would be to run the donaldson replacement element. It is a direct replacement element to the O.E.M. replacement. It may be $4-$5 more, but it is well worth it. This filter and all the info for it can be viewed at Donaldson makes the filter, but amsoil is selling it. Donaldson makes most of the filters used in cement trucks, gravel trains, semi trucks, bulldozers, ect... I have a 2001 7.3L, however I do all the maintance on my buddys 2005 crew cab 6.0L as well. His MPG sucked when it was new, but gradually got better as he put miles on it. I changed all the fluids to high quality synthetics, put a banks exhaust system and a programmer he bought(not sure of the name), to make a long story short, he now has approx 25,000 miles on the truck and is averaging between 17-21 MPG combined city/highway. With the few mods that are done to his truck, the exhaust and switching all the fluids out to synthetics made the most difference in the MPG. They also dropped his EGT quite a bit. The addition of the programmer brought the EGT's up a bit, but still far below anything to worry about.
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