I recently acquired a 1997 F250 PSD, Auto, Supercab, Longbed, Topper, 57k/miles. Lifted to accomodate 38" Dick Cepek - Kevlars on Weld rims. Stock intake and exhaust. My average mpg is about 10. I understand good driving habits. I want to know if there is anything mechanically I can do to improve the gas mileage significantly or if the low gas mileage is a result of the lift and big tires? Any comments?

 

The first thing I would check is the air filter. This site has a mod called kwik6637 which is a great improvement over the stock setup. Also the fuel fitlter shold be changed if it hasn't been done in a long time. Also the filter screen next to the fuel filter housing. 4 inch exhaust would help with egt temperature. Basic maintenance goes a long way with diesels or gas trucks. Jcab

 

Check out this subject. Same concerns as yours.
https://www.ford-trucks.com/forums/s...d.php?t=500349

3:55 Axle ratio along with those 38's = Bad milage.

Check your door sticker for the axle code then search this site for your axle ratios
JIM

 

Cuda_jim, I'm pretty new to truck ownership, this is my first one. Can the axle ratio be changed/adjusted to accomodate those tires? Isn't that something that should have been done when the truck was lifted? According to the door sticker my axle is a C5. How can I tell what the axle ratio is if it's been changed?

 

You have a 4:10 LS Limited Slip. If you want to verify the axle ratio you will need to pull the differential cover and look for markings on the gears or count the number of teeth on both the ring and pinion gear and apply alittle math to get the ratio.

To get the same pulling power and milage you would need to change your gears to aboout 4.88's. I assumed our stock tire heights are 32 inches tall and your new ones are 38 inches. If the differnce between the original and new tires is greater then the gear ratio gets even bigger.

Changing out gears can be $$$$. Ecspecially if you have a 4x4.

I doubt that you will ever see the milage a stock truck gets due to the rolling resistance of those monster tires.
JIM

 

go back to the original tires and rims! you are killing the transmission too!.

 

he3 isnt killing the tranny. It would be the equiv of towing maybe a 3000 lb trailer. And the only time he would notice a big drop0 im mpg is starting and stopping. freeway travel should be ALMOST the same. Dont forget, if your speedo wasnt corrected for the larger tires, your actually traveling much further than what your odometer says......

 

Good point Todd525, With 38" vs. 32" tires when the speedo shows 70 MPH the actual speed is 83 MPH ,

My new tires are a little bigger 285 75 16 (32.8" dia) vs. 235 85 16 (31.7" dia), my milage dropped by 2 MPG, if I figure in the extra distance traveled it's probably closer to 1 MPG.

That's about 1 MPG for every inch larger tire.
That's 6 MPG for Moby's truck.

 

Thanks Guys. I thought about going back to the stock tires but I really love this setup. I think I'll stick with it and just drive more efficiently. I am planning to do the DiY Tymar intake and the 3" downpipe. What's a good price on a the downpipe?