No... Studies have been done on switching to synthetic. No issues. Also, Some say that once you run synthetic, you can't go back. Switching back to conventional is not a problem. It's a myth.
Also, do some more searching. Mobil 1 is not a true synthetic anyway. There are better oils out there for the money.
I run Motorcraft synthetic or semisynthetic in my SVO, and will run it in my truck when I change the oil here shortly.

 

No problem at all as long as the oil has been changed regularly in the past. The real story on problem with change is the synthetic has a tendancy to clean better and what heppens is it will dislodge sludge that can get caught in oil passages or removes the sludge from around seals and they suddenly start leaking.
I changed my truck to synthetic when I got it at 160k miles and no issues. Changed my sons mustang at 120k and no issues. But they were both clean engines to begin with.

 

i have a 2001 F150 4 x 4 with the 5.4 motor. It has 200k miles. I go 20 miles one way to work on a state highway at a steady 58 MPH. I get 17-18 MPG in the summer and 16 in the winter at that speed. I have pulled a 4000 pound trailer and the milage drops to 11-12 MPG. To get good milage you have to have no load and a stead speed on the highway. Town driving, start and stop, pulling a trailer will all kill it. THe oil, filter, throttle plate, are mostly hype. You best bet is to do a good tune up, have new plugs, clean oil 5-20 or 5-30 weight, and keep your right foot steady....

 

Guys, HELP me out!! I'm only getting 13.5-14 MPG on the HIGHWAY!! I have a 2003 SCREW Lariat FX4 4x4. I have a hunting spot about 40-45 miles up the road one way. I hop on the interstate and set the cruise at 70 MPH (speed limit) and I'm running about 1950-2000 RPMS. I have stock size tires (265-70R17) but I do have BFG ATs. I have an Air force 1 CAI and recently added a Magnaflow SIDO 14" exhaust. I do have that crappy Poweraid throttle body spacer (hey it was on the truck when I bought it!). I drive very consertatively. I try to "hyper-mile" and coast whenever possible with my foot off of the accelerator. I recently cleaned the Throttle body and MAF and that did seem to help some. I got my best tank yet of 14.6 MPGs...but again this is 85-90% Highway mileage. Other than a trip or two into town its all interstate mileage. After I added the Magnaflow I actually dropped .6 MPGs!!!!!!!!!!!!!!!!!!!!!! And no I wasn't reving it to hear the exhaust. I was very disciplined.

What brand of spark plugs are ya'll using??? I'm doing a plug change now. I have some MCs here but was thinking of taking them back and getting Denso Iriduims. I been told Troyer uses Densos when they do their mods.
My next mods are definitely E-fans and synthetic fluids in diffs, transfer case, and transmission.
Would switching from MC Syn-blend to a 100% synthetic oli like Mobil 1 or Pennzoil Platinum help any at all?---DirtySCREW

 

FYI, Mobile 1 is not a true synthetic. They found a loophole and can call it synthetic. Do some googling on that.
Being a supercrew and 4x4, you're doing about as good as you can gas mileage-wise. Especially if you have a 5.4. You don't say what gears you have, either, but 70mph might not be in it's most efficient rpm range. 1950-2000 seems kinda low.

I have no idea what plugs are in mine, but will do some searching before I change them out.

 

Yea, i know about the M1 thing.

I do have the 5.4L and have stock gears...3.55LS as far as I know.

I don't know why a supercab can get 4-5 MORE miles per gallon over a Supercrew especially when the Supercab is running 33" tires!!!!! I know someone on the other forum that gets 18-19 highway or better with his 33s. Granted he has a tune and some mods...but I'm on stock tires and driving for efficiency. It seems the more i spend to get better gas mileage it backfires and I get worse!!!!!!!!!!!!----DirtySCREW

 

Well, on the winter blend gas I'm getting now, mileage seems to have dropped. Closer to 14-15mpg average now.
It's also been very windy the last couple weeks, and I've taken some highway trips over the holidays.
i'm due for an oil change, and will be putting in Motorcraft synthetic or semisynthetic.
I've also got Motorcraft platinum plugs. Replaced one already when the COP died. Will replace the others when it gets warmer.

 

Correction on my gears.... I actually have 3.73 LS. I found out when I called the local dealer to get part numbers and prices for axle seals and bearings. I was planning on going ahead and replacing them since I have a rear diff leak. I'd hate to have to replace them AFTER I repaired the rear diff with quality synthetic gear oil and then the bearing or seals go out. Anyways, I'm still getting crappy mileage. Last tank averaged out to 13!! What I don't get is the highest I've ever gotten with the truck is 14.7 beleive. And that was all highway!! I've cleaned the TB, cleaned the MAF, changed plugs (MCs), ran Techron through her, made sure tires are inflated properly, drive for efficiency and I can't even get to 15mpgs on the highway.

Is there a MAP sensor (manifold absolute pressure) on our 2003 trucks? I've been reading where if that sensor is bad OR if you have a slight vaccuum leak that it will cause improper readings to the PCM and you'll have a rich mixture....thus burning excess gas affecting your mileage.

HELP---DirtySCREW

 

Any bad sensor could cause that. more likely thought would be a dirty 02 sensor.
There's 4 of them suckers on these trucks!

 

Yea I though about that. Here's my plan, lemme know what you think....

I plan on removing/deleting the pre cats and installing Magnaflow Hi-flow cats. I was also gonna replace the 02 sensors then. I don't know if i can delete 2 of the 02s or not; please advise.

Then I was gonna do the axle seals and bearings and probably RP the diffs.

Then I was gonna Amsoil the transfer case and trans

And eventually E fans, Long tube headers, and a Gryphon programmer.

I know thats a lot of money to spend for probably only slight gains in MPGs...but its a work in progress----DirtySCREW

 

I wouldn't replace the cats or exhaust unless your's is rotted. You can take the O2 sensors out and clean them. Not sure if there's a way to test them or not.
I'm considering replacing my muffler and adding a stainless tip. Only because I want a little throatier sound and a little bling... I'm not used to such a quiet truck. don't want obnoxious glasspacks or anything, just a mellow tone. If I gain a mpg or two, then that's an added bonus.
I'm looking at aerodynamics to increase my mpg. An air dam under the front bumper, and some smaller sleaker mirrors. I know the bed cover thing was busted my Mythbusters, but I need one for security anyway.

 

How do you clean o2 sensors? I already have a Magnaflow SIDO exhaust, I was going to replace the cats with some hi flows...for better flow and hopefully better mileage; I have 138K miles on her....I'm sure the stock cats are pretty clogged up---DirtySCREW

 

I've always just cleaned the carbon off the tip whenever I've had them out.
Goggle found this thread
https://www.ford-trucks.com/forums/6...en-sensor.html

A lot of controversy... I'd say cleaning couldn't hurt, but looks like replacing them is the most sure-fire thing. I'd only do that if you got a code that one was bad.
I've used carb cleaner to clean them.
Also, I think seafoam does a good job at cleaning them if you run it thru your gas tank.

 

i thought you guys just helped prove that the winter gas and cold temps were the major effect on the MPG? Most other aftermarket items should have a very minimal effect compared to the gas and ambient temp.