I saw an add for a 1988 F350 with a 460/C6/D60 combo. I got there and after looking at it figured out it was a 89 with a 5.8. It was raining, so I couldn't get under the truck and look at the trans, however, the code on the door said "K". I'm lead to believe this is a C6 trans.

So is this a way to tell the trans? If it is a C6, what kind of mileage is expected with the 3.54s I also think it has?

 

I'm very certain that trans code K is the C6. Now for fuel mileage expect at most ~10 MPG unless you keep your foot out of the loud pedal & drive like a grandpa then you might get ~13 MPG city.

 

King joes right. She has a C6. My f250 got about 13 highway and not much worse in the city when it had the C6. That was with 4.10s and a 302 though

 

Well this is all I know. I have 96 4x4 f150 5.8, 3.54 gears, e4od trans, and I am getting about 11 mpg. I cant imagine yours going up from that. Most dually trucks that I do know, get about 9 mpg.

I worked in the auto repair business for many years, and I have heard all kinds of stories about how my truck gets 17, and my truck gets 20, even if you buy this thing it will get 30. Trucks just dont get good milage. My previous 93 f150 2wd e4od 5.0 got 13 mpg.

I keep good notes, and avg across three fillups. I dont just pull out the best number on a specific run.

My motorcycle gets 42 mpg on avg 600cc 4cyl fuel injection, but can drop to 25 if I am having a great day.

My volvo 5cyl turbo 2.4 liter gets 19 on avg, but will jump up to almost 28 if I take a long interstate trip.

 

If you're looking for the best fuel mileage, I think the best variant of these trucks is the diesels. My PowerStroke gets 17-20 running around empty (combined city/highway), and I've read documented claims of the non-turbo IDIs doing even better. This is assuming a stock truck running around on 3.55 or taller axle ratios, of course.

 

this is a Reg cab 8ft box truck. Single wheel.

I was just curious about mileage. I was hoping to see (realistically) 12 MPG. This is an extra truck to me and not a daily driver. However, if I buy it, and I can knock down a half decent MPG, I'll drive it more. I'm currently swapping a 12V Cummins into my Chevy, so that will be my mileage queen. This truck will have truck duties in the mean time.