A couple weeks ago I had removed both 19 gallon tanks on my `86 F250. Replaced the circuit boards in sending units and new shower heads. Then back together they went. Had replaced all of the aftermarket screw ups one of the PO's had done. Removed the electric fuel pump rubber hoses everywhere, cut and hose clamped plastic and steel lines.

Everything went back together with original parts. Also was able to resurrect one complete working selector valve from a box of broken ones. Then started using the truck routinely. Took it for a couple of longer distance runs last week and today. Finally went thru the front tank until motor started to stumble. Then switched to rear tank without any issues. First time I had the rear tank connected and working.

With combination city highway driving a/c running the whole time, and pulling a flat bed trailer part of the way, I got 260 miles on the front tank. I have not refilled the tank yet to see exactly how much fuel was actually used tho. Is this about what I should be expecting?? I was definitely NOT driving it like Miss Daisy, but never went past 70 on highway.

My `78 F250 with 460 would be doing well to get in the neighborhood of 150 miles on same size tank. It wasnt so bad when gas dipped below $!.50 a gallon a few times in the last 20 years. But rest of the time, it was painful refilling. The truck always seemed to veer to what ever side of street a gas station was on as I had little luck trying to pass it.

 

If there is 1 gallon left in the tank 260/18 = 14.4 mpg, if there is 2 gallons left in the tank 260/17 = 15.3 mpg.

I think most of the fuel economy lost on highway driving is when increasing speeds above 60mph. Highways around here are 60mph speed limits and I like that speed for this truck and I'll probably be keeping that speed when on 70 mph highways and while towing unless I'm in a hurry and feeling like I can afford the higher fuel costs. (very limited income here)

The only somewhat 'official' mileage rating I could ever find for these trucks with the 6.9 only stated that it was about the same as the 300 cid in-line six: 14-17 mpg

If you are working the truck (doing beneficial work with it) then that seems good enough for me.

 

"Tank" is not a way to measure fuel economy, nor is the gauge. Too much variation in where the pump kicks off on "full", on when the showerhead starts to pull air, too much variation in gauge accuracy, etc. The only accurate measure of fuel economy is: Fill tank, drive, fill again and record distance and fuel required to refill, divide.

For better accuracy, repeat over several tanks, add all distances and fill-up amounts and divide. Calculating over multiple tanks minimizes the impact of variation in fill-up click-off level.

15-16 MPG is pretty good, esp. since the '85 won't have an OD with either tranny. T-19 should get better than the C6 if driven right. A ZF5 will add an MPG or two, unless your driving is mostly in-town / low speed.

 

Every time I fuel up, I always get a receipt and write the mileage on it for safe keeping ...

-Enjoy
fh : )_~

 

To the OP, What trans and gearing do you have? 2wd or 4wd? Let us know the numbers when you fill up. For our driving speeds, towing and city/hwy mix it looks like you are doing about right.

Mine is an '88 e250 c6+DNE2 with 3.54 gears. Mixed city and hwy with some towing and loaded.

My van has a little different tank setup. I have a 16 gallon front tank and a 22 gallon rear tank. With mixed driving I usually drive about 200 miles on the front tank and then switch to the rear when it gets to 1/4 of a tank. When filling it up I consistently put in about 12 gallons + or -. I run the rear tank to a 1/4 of a tank and then refill. Usually a little over 200 miles and 12 gallons.

I have tracked every fill-up for the last 57,762 miles. I have averaged 15.17mpg. This includes the time prior to adding my O/D, changing tire size and winter fuel/idling. This is not 100% accurate since there were some times that my odometer was off due to an incorrect speedo gear when I added the O/D and when I changed tire size. My highest tank was 18.42mpg and my lowest was 9.94mpg.

There are mods you can do to increase your mileage some, but the biggest factor is your cruising hwy speed. Here is an experiment I did comparing speed and mpg
https://www.ford-trucks.com/forums/1...periement.html

I gained about 2mpg dropping my speed from 70mph to 60mph. This test was done with a mix of city and hwy. All hwy I would get better. My last trip that was all hwy I averaged 16.37mpg with the cruise set at 70mph. I had 3 tanks that were 17mpg or better (17,17.5,17.5). If I would have dropped to 60mph I probably would have had some tanks in the 19mpg range, but on a 3000 mile trip I just decided I would pay the $$ in fuel.