99 F350, 6 speed, Gas Mileage?

Jerome Casi · Mar 8, 2011

Hello all!

I did a search and couldnt quite find what I was looking for. I just sold my 97 f350 and got a 99 f350, Crew cab, dually, 6 speed, 120k miles. I am only getting 14 mpg, how are some guys getting upwards of 20????? I do highway, I dont mash the gas. Im pretty sure I have the 4:10 gears, is that why? I was really hoping to get better mileage.

Dealership went through it, I had a bad injector, that was replaced and given a good clean bill of health.

Appreciate it!

lil_dq · Mar 8, 2011

First off Jerome, Let me say Thanks for your service! A buddy of mine is in the USAF in Germany right now.

Second of all, I don't know, 14 seems reasonable. I could be wrong.

Austin · Mar 8, 2011

Turbo or non turbo?

DNFXDLI · Mar 8, 2011

I don't think a non turbo option was available. Our 2002 550 got about 14 imp running around 15k #...it had 3.73's if I recall. It might very well be that ratio that is dropping it.

Jerome Casi · Mar 9, 2011

lil_dq said:
First off Jerome, Let me say Thanks for your service! A buddy of mine is in the USAF in Germany right now.

Second of all, I don't know, 14 seems reasonable. I could be wrong.

Thank you, we appreciate your support! I wish I could be in germany right now that wouldnt be to bad!

Jerome Casi · Mar 9, 2011

DNFXDLI said:
I don't think a non turbo option was available. Our 2002 550 got about 14 imp running around 15k #...it had 3.73's if I recall. It might very well be that ratio that is dropping it.

It is a Turbo, It just amazes to read a couple guys getting 19 -21 mpg, and I am empty and getting much lower. 70mph is also like 2300 rpm if I remember right, which bothers me. Curious if I did a swap to 373's if it would pay itself off eventually with a gain in gas mileage????

Thanks again for the info!

primetime · Mar 9, 2011

Yep, some guys are getting mileage like that. Others get mileage like yours. One thing that hurts you is the increased rolling and wind resistance because of the duals. They make a pretty big hole in the air. As to the gear swap, eventually it could pay for itself. You may want to look into a K&N or some other air intake system, and a turbo back exhaust system. Some tuners also increase milege. Head on over to thedieselsite.com. They have some good information on the coolant thermostat that may help you, along with other nifty stuff for Powerstrokes.

Farmerjon · Mar 10, 2011

Hi!
We have a 2000 F350 SC DRW PSD 7.3 4x4 6sp 3.73. It gets as high as 17 and 18 MPG empty. Loaded down with our truck camper with all that wind resistance we average 14 out on the highway and thru the mountains. Could we get 20 empty ? maybe, but I have a problem running 50 or 55 on a perfectly good 4 lane hiway

At 2000 rpm we are going 67 mph.

I would say by the difference in our speeds at 2000 rpm that you do have the 410s

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99 F350, 6 speed, Gas Mileage?

Jerome Casi

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