Is this unreal Mileage out of a 6.9 or something that is common?

[stonecrusher]

I recently bout an 83 f250 4x4 with a 6.9 in it and I noticed that the milage I am getting is unreal. I had the truck in 4 high pushing snow all day and when I topped off the tank(fuel gauge don't work) tonight it only took $7 to bring it all the way up the filer neck and that is with fuel prices here at $2.98 a gallon. I drove around 55 miles and plowed 4 small driveways and 3 big one(long lanes). When I do the math I purchased 2.2 gallons of fuel and that comes out to 25mpg and thats not counting the driveways that I plowed. I can't beleive this because the truck was locked into 4 high the whole time. Im starting to wonder if there is something wrong, the engine is hitting on all cylinders and has no apparent problems. Is there a possible problem that I could be over looking because I can't believe I could be getting such good mileage running in between 40 and 55 mph.

 

[timothyr1014]

yeah its really good, but not totally unreal....depending on you gears you were probably right in the sweet spot. on my cc dually if I can hold it right at 45 I can pull a solid 23mg with 5k in the bed.....the biggest thing to kill your milage will be high rpms; torque peak is around 1400, and if you can keep it between 1700~2000 you can expect some "unreal" numbers

 

[stonecrusher]

I honestly just figure since I was hauling around an 8 foot plow and running in 4 high that my mileage would have been alot worse, but I am in no way complaining, Im glad I made the switch from 6mpg built big blocks to an idi

 

[oldmisterbill]

Its interesting I had 5 PU trucks plowing Driveways in MA when i lived there.Based on Hrs per gallon I was always amazed at how little fuel they used - I figure it is because the RPM was kept low and to keep traction the throttle was used carefully,even though it was constantly back & forth work.3 of them were 350 small block chevys-1 400 small block and my ole 94 F250 IDI. I miss that truck. On a side note they were all automatics - much faster than a stick for volume plowing (for me at least).

 

[david85]

Its possible, but not very likely. You need to average a few fillups before drawing any conclusions. It might seem like the filler neck is an accurate gauge for how much fuel you put in, but really it isn't.

 

[stonecrusher]

I actually added up the amounts of fuel using the receipt which had the exact amount purchased printed on it. Thats the only reason I somewhat beleive it.

 

[Shadetreemechanic]

Its possible, but not very likely. You need to average a few fillups before drawing any conclusions. It might seem like the filler neck is an accurate gauge for how much fuel you put in, but really it isn't.

X2 It sounds just a hair beyond reality to me. As finicky as these filler necks are you really need several tanks to draw any conclusions.

 

[david85]

Well if you added up several tanks and averaged them, I could believe it. Cruise speed of 55 MPH or lower actually helps a lot. There was some one on ecomodder.com that had an 84 F250 in san fransisco that was getting close to 30 MPG with a few minor mods but also cruising around 40 MPH.

Aerodynamic drag is a non linear function, so if you double your speed, your wind resistance more than doubles. In other words, the slower you go, the less energy it takes to travel the same distance. Gearing also plays a big role in how well it cruises at any given speed. Sounds like you might have a good combo.

Cold weather might also be helping a little.

 

[icanfixall]

I bet you did get that mileage and you seem to have proven it nicely too. Driving home from the rally I got 18.9 mpg over the 2100 mile trip. I was running between 75 and 85 mph in double overdrive. An E4OD in od and a Gear Vendors in od with 3.55 gears. I wonder what I could have done at 55 mph... And I had a new Moose pump installed at the rally too... Sweet ride home it was... Mels son got 29 mph driving home from the rally in the Nite Moose... Its an F150 with a 6.9 motor thats not even had the timing checked in it... Shows us what some shadetree engineering can do with a 3200 lb truck... I think Mel and Mathias did a great job with very little issues in the swap... Other than the PenDot mess... Those poor excuses from people should be used for target practice in a zoo full of monkeys....

 

[sle2115]

I once plowed all week in the college's Ford F250 Gasser (87 IIRC). Went to fill up and logged the mileage, etc. I got a call the next day asking me how I used a full tank of fuel and only drove 7 miles! Finally figured it out...I'd put miles on going frontwards, take them off going backwards! It was a Ford issue and I'm pretty sure they had a recall and fix for it. I left shortly after it happened, but I know my old boss said something about it later, having to take it in to get that fixed. It was an OD automatic and it would put the speedo needle into negative MPH, big time!

I'm not saying that happened here, just thought it was funny. I'm guessing this is possible with the low RPM's and such driving/plowing. My truck is really good on fuel just moving around here, out on the highway with those 4.10's...well, that's another story!

 

[kas83]

Given the BSFC is so low at idle or slightly above, which is how I usually plow, and when you're running down the road at lower mph and RPM, I can believe the engine is capable of 25+ mpg. If you've done it several times, then I will say you may be on to something.

FWIW, there is a site that has a writeup on a semi in Europe that gets 28 mpg while loaded to 95,000 lbs gross, cruising at no more than 37 mph. It was linked of off Kevin Rutherfords forum, if anyone listens to him on Sirius/XM.

 

[Goofyexponent]

I don't know. I would say high pretty damn good. My extended cab F250 4x4 managed an easy 23 MPG on a recent highway run. I KNOW I could get 25 MPG out of her with a little tune up work. It needs an Ialignment, an oil change and I had a couple of hundred KG's of scrap steel in the bed.

 

[timothyr1014]

I think the biggest thing with these motors is they dont mind being ran hard and high so we kind of loose track of how far out of the sweet spot we normally operate them.
when I make a concious effort to keep mine in that range it never cease to amaze me, the biggest issue I have with mine is just lack of gears...let me keep my 4.10's and give me double (or triple) over

 

[vegas39]

I bet you did get that mileage and you seem to have proven it nicely too. Driving home from the rally I got 18.9 mpg over the 2100 mile trip. I was running between 75 and 85 mph in double overdrive. An E4OD in od and a Gear Vendors in od with 3.55 gears. I wonder what I could have done at 55 mph... And I had a new Moose pump installed at the rally too... Sweet ride home it was... Mels son got 29 mph driving home from the rally in the Nite Moose... Its an F150 with a 6.9 motor thats not even had the timing checked in it... Shows us what some shadetree engineering can do with a 3200 lb truck... I think Mel and Mathias did a great job with very little issues in the swap... Other than the PenDot mess... Those poor excuses from people should be used for target practice in a zoo full of monkeys....

What RPM's are you turning with that setup at 80 mph?

 

[icanfixall]

At 75 mph I'm turning 1750 rpm.... At 85 mph I'm turning 1850 rpm..... At 80 mph.... Never looked at it but I'm guessing around 1800 rpm....