This point could also be made. The car makers are under more than extreme pressure from the Feds to bleed every last 1/100th of a MPG out of every vehicle.
If a simple intake and muffler change would add even .1 a MPG don’t you think all of the car makers would have done this on the production lines already where the production costs would be much lower?
Don’t forget the voranado intake too .
In searching the web, I find
Have you seriously checked the reliability of the source?
Yes there are better ways of building a mouse trap, but so far no one has done it by playing games with the air intake on a stock engine. There are other ways towards improving things that may work, but frankly unless you are going to make some very serious and expensive changes you are not going to see enough of a change to pay the cost.
Far too much that you see on the web is from someone who is making a profit on the product, or is a sample of the placebo effect.
Is there anything that Does make sense to do? I plan to keep the truck for quite some time.
If the car makers squeezed out all the mileage that they could this year, what would they do next year?? They have to save some inprovements for the future.
Colder air means more fuel use around town. The one that came with the car is designed to put warm air into a cold engine. Your air filter is already huge and requires almost no maintenance. Before doing that kind of thing, wait for your midlife crisis. If you are already 50 years old, you really need a Mustang.
Keep your tires inflated a few lbs above the door sticker figure, keep the car well tuned, SLOW DOWN, keep excessive weight out of the car, use a 0W30 synthetic oil (energy conserving), brake carefully and no jack rabbit starts! Tell the rest of your family this as well.
Experienced economy run drivers can take your Expedition and get 20% better mileage without trying hard, just by the way they drive.
He’d push his trusty Dodge all the way home after it broke down. 
There is no cheap fix for what you want to accomplish.
And if one assumes that you would be willing to spend a small fortune on engine modifications (cams, head work, gears, etc.) you have to keep in mind that you will be giving something up somewhere else.
Car makers try to manufacture a vehicle that will perform most jobs well but they will not be excellent in every area.
Modify the engine and gears to aid fuel mileage around town and it may suffer on the road a bit. Modify it to perform better on the open road and it may suffer performance-wise in city driving.
Trying to compromise simply puts you back where you were; right where the factory intended it.
The same thing applies to tires. Most tires are a compromise and do many things well but do not excel in every area. A tire that is absolutely great in one area of handling may suffer in another.
I still maintain that if your mechanic was pinned down about an escrow account or a 2 week postdated check for this modification hinging on the success of the intake/exhaust changes he would not go for it at all. Ask him and see.
BEEN THERE - DONE THAT
The Dynomometer graphs that most ‘intake’ and ‘cat-back’ systems have on their web-site will show you at what RPM their product begin giving better performance. In the case of my V8 that is 2,000 RPM, which is where the engine runs at the speed limit. In other words…no change.
*Having done some of the intake and exhaust stuff on a past vehicle, what did work and gave better acceleration and a mile or two in mileage, was exhaust headers.
*The Flowmaster muffler did give better MPG…at and above 70 MPH. The rest of the time it gave me noise.
*The ‘ram-air’ intake made the filter dirtier faster.
*Removing the broken catalytic converter did imprive pick-up but made no change in MPG.
Then there is the fact that you are driving a very heavy vehicle.
The best way to improve MPG will be to go to a larger diameter tire. You could also go to the expense of changing the differential(s), but, consider the fact that you will change tires anyhow.
By the way; the computer controls and adjusts the air/fuel mixture so that the exhaust gas passing the oxygen sensors is at a set mixture. Because of this, unless you recalibrate the computer, your MPG will always be the same.
No one mentioned changing driving habits to increase mileage.
“Aggressive driving (speeding, rapid acceleration and braking) wastes gas. It can lower your gas mileage by 33 percent at highway speeds and by 5 percent around town. Sensible driving is also safer for you and others, so you may save more than gas money.” stolen from http://www.fueleconomy.gov/feg/driveHabits.shtml
This was a good response - Thank you. I wondered how the computer would affect things. Would getting a tune help? (Not sure I said that right) Going back to my Ford mechanic that started all this, he said that I may need to do something to adjust those computer controls to take advantage of these changes. I’m not much into putting big tires on the truck. If I proceed, I would like to keep things looking stock. I’ve received a lot of negative feedback to my question - basically saying it’s not possible. You’re reply seems to say it is possible, but would require one more step. Did I read this right?
Keeping your car in good condition will help the mileage.
The best solution would be to get a minivan or smaller car. This may not work if you need the Expedition’s capabilities.
Catching up on this thread.
The OP says it will take 18 months to recoup the $800 @ $3.00/gallon if the mpg increased by 2 mpg.
Assuming an mpg increase from 16 to 18, the OP would need to drive 28,800 miles/year for an 18 month payback. OP, is that your average for annual miles?
I agree with the numerous replies that indicate the 2 mpg increase has a lot of wishful thinking behind it.
The oil spec’d for the 2005 Ford Expedition is 5W-20. I could see going with the 0W-20 for a very slight fuel economy improvment, but a 0W-30 won’t help much.
I am NOT hoping to go from 16 to 18 mpg. (If I could, it would be a dream come true.) I AM hoping to go from 13 to 15 mpg on average. These numbers are much more realistic for a truck this size. I probably should have stated this in my original question.
For the cost of upgrades, I am willing to spend the money. Granted, there should be some payback. Whatever the payback may be, how ever long it may take… I am comfortable with it.
I DO keep my tires slightly over inflated, keep the truck well maintained, and keep my foot off the gas. I understand a smaller vehicle would get me better mileage. I will at some point buy a second vehicle that does get good mileage.
The point is, I plan to keep this truck for a long time. If there is a way that I can perhaps change some settings in the computer (like shotto sugests above) and make the truck breathe a little better AND improve the mileage from 13 to 15 mpg, I want to do it. The $64,000 question is… Is it possible? There seems to be a post or two that suggests that I may not be completely crazy here(a lot more that say I am). If anyone has any additional technical knowlege or experience doing this kind of thing, I would greatly appreciate hearing about it. Thanks!
As usual, the best way to increase mileage is to adjust the nut between the steering wheel and the driver’s seat 
One of the car magazines did a project on a Suburban to try to improve the gas mileage. My favorite one was an air dam which wasn’t done in those days at the factory. It was good for about .4 MPG. I forgot the other improvements.
About those fuel line magnets. If you had enough of them and you were following a big enough truck which was hauling steel…
Hey, folks. You don’t buy an SUV for the gas mileage. You buy it because it is a utility vehicle with a purpose. One of my children (with 3 kids) drives a Suburban; the other (with a lot of stuff to carry in her job) drives a Tahoe; I have a Silverado 1500HD with which I haul and tow my farm equipment - 17mpg hwy and I am OK with that. If I wanted fuel economy I would drive one of the little cars; I wouldn’t think of botching up a great-running truck with mechanic trickery.
The logic I was given seemed to make sense - easier to get the air in, easier to get the exhaust out, slightly improved power - all giving slightly better mileage.
In both cases the key word is “slightly.” It is far too slight to pay for itself over the life of the car. It is likely too slight to measure the mileage and you likely would need some very sensitive tools to measure any power increase.
Back in the grandpa’s days, most cars had restrictive air intakes and exhaust. The manufacturers have corrected that a long time ago, but grandpa’s advice still lives on long after grandpa.