Humm.. Well, those are basically the same size as my tires.. 265/75/16.. So, that's probably not it...

Dunno.. Do you have a tonneau cover? If not, do you run with the tail gate up or down?

I've got a soft tonneau cover and it's supposed to make a little difference in mpg's??

Mitch

 

No. no tonneau and a I drive with tailgate UP. I've even seen the Mythbusters special which tested all of the possibilities. I'm not doubting their results but I do not think they had a real world test. Running a preset route is one thing, but real world is stop and go driving, traffic jams, alternate routes for various reasons. I really SHOULD be getting better highway mileage. I can't figure it out.---DirtySCREW

 

are they of the same tread type or all season vs all terrain?

 

dang guys, im averaging 15.5-16 with mixed city (with traffic) and some highway

I usually do 20-21 on the highway, and have gotten as high as 23 average for a whole tank on the highway.


Mitch is dead on with the wheels tho, after i put these ridiculously heavy 20s on there my highway MPGs went down by a full mile per gallon

 

yeah i was going to say...Somethings wrong with your truck! Before the cams and headwork i was getting 17.6-18 on the hwy, so the edge programmer said and as far as i am concerned thats the most accurate way to tell. Now, i get about 10.5 hwy with a bad tune

 

rotating weight is 10 times worse than stagnant weight

 

Not necessarily true - they CAN get weak. Generally, the symptoms of a weak COP is right after it shifts into OD around 40 mph, under light throttle it will skip and surge a bit.

Different people have different results, and the only way to find YOUR best combination is do your own experiment.

 

That's true for stop and go and acceleration performance but rotating weight doesn't really affect HWY MPG to any degree that matters.

The thing that strikes me is how the aftermarket suppliers of CAI, air filters, manifolds, exhausts, programmers, etc. like to tout better MPG in order to sell their products but generally a well tuned stock truck gets more miles to the tank.

True, there will always be some joker that shows incredible MPG gains from his mods but, in general, this is not the way it works.

 

GUYS....I WAS WRONG!!!!!!!!!!!!! And I'm man enough to admit it. :P

I thought I had 3.55 LS gears....well I finally remembered to call to Ford Dealer to get the part number and prices of axle seals and bearings as I'm going to go ahead and replace them as I have a diff leak. I didn't see much sense in just fixing the diff leak, putting in high-dollar synthetic diff fluid to have a bearing or seal go out and have to do it all over again. So I guess it for my peace of mind than anything.

Well the ford parts guy needed my Diff tag to make sure we got the right parts. I go and get it and call him back.

Turns out I have a 9 3/4 diff (thought I had an 8) and I have 3.73 LS instead of the 3.55LS I though I had.

This doesn't get me any better mileage but it does make me feel a little better, since I DO have a steeper gear. Again, I'm trying for the life of me to get this 150 to where my Yukon was that had 5.3L 2wd 3.71 gears. It got 14.5-15.5 CITY and 20-22 Highway!!.

I'd be soooo happy with 15 city and 19-20 highway. Well maybe after my e-fans, synthetic fluid throughout, & Gryphon programmer I may be able to touch those numbers......maybe.

As far as my tires..they are BFG AT's...probably AT KOs..as I think that is all BFG sells now for their All Terrain series. Again they are LT 265-70R17 on stock FX4 wheels set at 45PSI. I'm sure a different tire may give as much as .5 MPGs due to rolling resistence and different compounds etc etc. I'll cross that bridge when I have to buy tires...these are only about 9 months old! I need a front end alignment and may get the shop to rebalance the tires and refill with Nitrogen. But all that is gonna have to wait until I come into some cash again.---DirtySCREW

 

yea 5.4's have 9" rear ends.

 

Not gonna happen. Mine is 2WD with 3.55 and best it does on highway is 17.2. Between 15 and 16 mixed driving. Of course I drive 75 to 80 on highway but you have an FX4 with 3.73 so your mileage will be worse. I have synthetic fluids through out. Your diff is filled from Ford with synthetic.
I may be able to improve mine a little by replacing plugs and front O2 sensors and driving 65. I have 138K on stock parts.

 

Norm, I'm in the same boat...138K on mine as well. I just changed the plugs (MCs) and put on a new K&N cone filter replacing the dirty unknown brand filter on my Air Force 1 CAI. I don't know if aftermarket brand synthetics are better than whatever Ford puts in or not. Does the transmission and trasfer case have synthetic from Ford as well?? --DirtySCREW

 

I am getting 16.8-17.9 highway and 16.2-17 country roads. I have noticed a difference though since they switched the fuel to winter grade inm the last month and I have dropeed a litlle. I try to keep it around 65 if I can keep my foot off it! haha! I am getting ready to do a plug change and fuel filter change also since I have 82K on it I think its time.

 

I do not know about transfer case as I do not have one but transmission fluid is not going to give you better mileage. I have Amsoil ATF in mine.

 

no the transfer case doesnt have synthetic fluid in it, it is the same fluid as in the transmission. you wont get any better milage with synthetic fluids throughout, i would look into a bed cover, im really not sure if that helps or not, ive heard it has, im looking at getting a hard cover, not for fuel economy.

i have a 2002 extended cab 2wd 4.6 with 3.55NLS with amsoil rear end fluid, new plugs, new 02 sensors, new converters, true dual 2.5" chambered mufflers and i get an average of 16.7 mpg