91 F250 7.3 with a Banks turbo, 5-Speed 3.55 gears and 33x12.5,s. Unloaded I get 17 mpg city and highway. I can make it get worse, all i have to do is keep the boost up

 

You have no overdrive, that can make a pretty big difference.

 

85 6.9 with 315,800 miles. unloaded 15-16 in Cali. Loaded, other states, 13-18, best mileage, drivivng easy, long trip, 20.2
Dave

 

13.85 is the best this year so far
12.20 is the second best
I am always hauling or towing something heavy on every fill up though.
Average for the year so far 10.19

86 7.3 turbo T19 4x4 3.55LS and 33" mudders

 

93 F250 extended cab 8' bed 5 speed man. city about 14-15/ highway21-23 but have gotten up to 25 empty....new injectors, fuel lines, return lines and tee's, and new injector pump...279,000 miles. Before replacing fuel system parts 8 city 11-12 highway

 

94 f350 dulley crew cab, stock, 4.88 diff, average about 12-13 mixed driving has a gear venders, comes out to about 4.10

 

F250, 1991, logn box, king cab, 4x4. I get 16 to 17, with a 2900 lbs camper on it on hilly roads. Not bad.

 

I have an 83 f250 6.9, 4 speed manual, 2wd, think I have 4.10's, I got 17.5 mpg (cdn) pulling our canadian mountains at an average speed of 55 mph with an old '73 9.5 ft camper and utility trailer loaded with camping gear. Without the camper on I get around 22-23, I thought I was doing bad for fuel economy, but after reading what others had to say I guess I'm doing not bad.

 

Mine old one-1984 6.9, ATS turbo system w/ 3" exhuast, 4 speed, pump rebuilt and recalibrated, gears were something like 3:50's, 3:55's, 18mpg loaded with 9.5 ft camper and 21 ft Sunrunner boat, 23 empty on highway.

Dads 87, 6.9, Banks turbo kit, 3" ehaust, 5sp o/d, gears were the same as mine, pump rebuilt and recalibrated by the same really good shop. 24-25 mpg empty on the road, 18-19 with 9.5 ft camper and 21 ft Mark Twain boat.

So yeah I know those 6.9's could really run AND get very good fuel milage. Dad bought his truck new, only has 60,000 miles on it. Except for some paint flaking off the tops of the front fenders (dang ford paint in those years) his truck looks almost new, inside and out and runs a whole lot better than when it was new.

 

Man wich i could do better on mine. 85 f250 the heavy one with flat bed and big old air dam tho my milage actually went up when i put the flatbed on the truck so go figure. running 33's and a zf five speed. 4.10 rear i get around 12-14 on highway empty doing about 65-70. theres some hills but it doesnt matter wether iam going up to school or coming back from school. logic would tell me for evry hill i go up going to school iam going to come down on the way back so it should all even out rite? Those of you that get in the 20's what has been done to your engine injector pumps timing etc. also is it better to lug the engine in 5th gear or down shift to 4th and let her scream going up mild hills. the steep ones i have to down shift or id melt the motor for sure.

 

redneck all those guys getting close to 20 must live in flat country. I do wish I had a 5 speed, the 4 speed just has me winding to tight a interstate speeds. After doing several speedometer checks in these trucks I also wonder how accurate their speedometers are. I admit I drive fairly fast, I know my speedometer is right on, and the best I ever got was 13.85 with 3.55's, 33" tires and the 4 speed.

As far as optimal RPM, if you can keep it around 2000 RPM cruising you should get the best mileage.

 

No flat country here Dave. I live just outside of Salt Lake City and Dad lives in a the little town of Parawon, southern Utah. Dad is a retired truck driver and I had my own rig for almost 25 years.

Just about everywhere we go seems like it's UP and some pretty steep. 6 to 9 percent grades and long pulls.

My sister bought a 7.3 turbo with 4:10's, 5 sp OD but could never get over about 15 mpg. I know part of it was the gears but the 7.3's and later did not seem to be able to get the milage that you could get out of the 6.9's. I know mine and dads put well over 500 ft lbs torque on the dyno.

Increasing the fuel pressure but decreasing the flow rate, along with the rest of the right pump calibrations, makes power but does not increase the generated heat very much.

I told dad about this thread. Told him I would be raising the BS meter in some peoples minds. His said, Well tell em to put up the money to make it worth my while and I'll drive to where ever they are and prove the power and milage hehehehe.

The point is if a diesel is setup right you can make big hp and still get good fuel milage. I averaged 6.5 mpg out of a Cummins small cam 400 and a full load (almost 80,000 lbs gross) course thats a load lower on the deck. A full load of lumber or pull a 13'6 box trailer and it would go down some.

 

with 4.10's and alot of my driving on the highway a 5 speed was amust. i couldnt hardly stand to drive it much faster then 60mph with the 4 speed in her. it would just scream down the road. i thought id see a jump in mpg when i went with the 5speed but it didnt really change all that much. Mistaken ID how would you suggest I increase my fuel milage its an old 6.9 so it should be able to get pretty good.

 

To REDNECKMECHNIC: If you come up with any improvements on your fuel-mileage, I'd like to hear about it. I've got a 6.9 powered 85 F250 4WD, Ext. Cab, full 8' bed, 8600 GVRW, C-6 trans. and 3.55 gears. It has 60K original miles on it and it starts and runs great. Fuel mileage however is kind of dismal. I've got 6 diesel trucks/SUVs and the absolute best fuel mileage I've ever gotten was with my 86 Chevy Blazer 6.2 diesel and overdrive trans - empty - flatland drive - 23 mpg. Usual overall average is 16 here in the hills - empty - or 13 mpg pulling a trailer. Now, about my Ford with the IH 6.9. I drove one brand new in 1983 with a utility body on it (as a John Deere service truck). It averaged around 11-14 mpg. Now, on the subject of my 85 F250 with the 6.9. I've heard several claims about 20 mpg plus pulling a trailer on hills. I don't believe it, period. If I ever come across such a truck - I'll buy it and keep it forever. Such claims seem to defy reason. I used my neighbor's Dodge 5.9 diesel with a 9000 lb. trailer and averaged 14 mpg. He just pulled the same trailer with his new Chevy Duramax and also averaged 14 mpg. I just completed a 6000 mile trip with my 6.9 Ford with a slide-in camper, fully loaded and four people plus one fat dog. Figuring fuel mileage on the road was damn near impossible. On some fill ups I calculated as high as 18 mpg and as low as 10.5. This because of the variations in pumps and fuel, sometimes foaming, sometimes shutting off before the tank was full, etc. I have a hand pump at home and know when the tank is absolutely full - so - my true average reading was done after getting back home, filling up, and calculating the average for the entire trip. Came to 13.01 mpg. I don't think that's too bad - but - I average around 11 mpg. empty when the truck is home and used around town. That ****es me off the most.
I'd like to hear about any attempts to improve mileage. I know overdrive would not help my truck since it lacks the power to use here in the hills. Seems a turbo could potentially improve mileage - but perhaps not since I might just find myself driving up hills faster. I'm not clear on what kind of increase it would provide in fuel efficiency. I've been a diesel mechanic for 40 years, so I'm not totally ignorant on this matter. Over the years I've done quite a bit of dyno testing on farm tractors, and have seen a nice increase in fuel efficiency and power with many turbo systems - but not always. I've also done a fair amount of fooling around with injection timing, opening pressure, etc. As of yet, I've found no "magic bullet" that will increase fuel-mileage along that line. Fuel must go somewhere. When is disappears from the tank, it either is leaking on the ground, making heat and power, or going out the exhaust pipe in an altered form. My truck does not run hot, has no visible smoke or carbon build up in the exhaust, runs great - so I assume the injection system is in good order.

 

I just got back from a 3500 miles trip with my truck camper on it. I averaged 15.5 MPG, canadian gallon, I do not know how much this comes to in US gallon, but it would be a bit less miles to the smaller US gallon, I would say around 14 MP /US gallon. The best I ever done was around 20 miles for one canadian gallon, truck empty, no wind, flat road, below 60 miles per hour. I also have a hard time to beleive over 20 Miles to a US gallon... especially with a trailer. If I have a 20 mile per hour pushing tail wind, it will increase millage a bit, but otherwise, it is around the twenties.

I changed the muffler for a 3 inch but did not get at the piping yet. I will soon. I removed the platic tube going in the intake but did not cut off the bowl yet. From the readings, modifying these should give me a 1 or 2 miles, but I do not expect too much out of it.

I do not know wich rear end I have, but i will also check this out. I had a 1993 before not turbo and the millage was very close to the same as this 1991.