MPG for M1078 vs. M1083?

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Awesomeness

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'96 M1078 LMTV:

With stock 3.90:1 gears, 4-5MPG around town, 5-6MPG cruising. With 3.07:1 gears, it basically bumps it up about 0.5MPG... 4.5-5.5MPG around town, 6-7MPG cruising 65MPH low in 7th gear just after it shifts up from 6th. (I have thousands of miles of fuel logs to back this up, for my truck at least.)

Also, I find that loaded/unloaded doesn't really change it much. Neither does pulling the 7000lb M1082 trailer really, which mostly just drops it about 1MPG. By "doesn't really change it that much", I mean that the tank-to-tank MPG fluctuations just from other effects (e.g. temperature, windy days, terrain, etc.) will swing it +/- 1-2MPG, and loading it or pulling the trailer just seems to move it to the lower end of the range it already fluctuates within.

Lifetime Avg.: 5.26MPG
Worst tank: 4.10MPG
Best tank: 8.08MPG (A straight couple hundred miles across Arizona, on a cool morning, with a bit of a tailwind and the cargo cover on, on a mostly downhill leg.)

Those numbers are across the whole 5 years I've owned the truck, which includes switching to the 290HP engine from an M1083 6x6, and then a year or two later switching to the 3.90:1 gears. Intrestingly, lifetime average before the 3.90:1 gears is 5.26 and after it actually drops to 5.25 since I've installed them. So while the 3.90:1 gears may help a little while highway cruising, it seems to hurt it in-town, which is where most of my common use actually takes place. (By "in-town", for me, that means about a 60%/40% split of 60% above 50MPH, and 40% below 50MPH.)
 
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Awesomeness

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I'm not sure if there is anyone around that really tracks it well and knows. I hope there is, but this question comes around a couple times a year and then the thread gets filled with tons of info that is at best "wishful thinking". Somebody will chime in that they get 10MPG and plan to get 12MPG after switching to 3.90:1 gears, etc. I don't know why they are so far off of reality.

If I had to guess for an M1083, I'd say knock 0.5MPG off all my numbers. The biggest factor is going to be air resistance, and on that they're the same. Beyond that you have one extra set of tires for rolling resistance next, and then a few thousand extra pounds. That all seems good for about a 10% change.
 

tennmogger

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I went for a long ride with friends across Colorado and parts of UT, WY and MT. He was in an M-1083 with a Gichner shelter. I was in an M-1078 with an Alaskan Camper. The Alaskan is about 2000 lbs. I would guess the Gichner was at least twice that weight.

As for absolute mileage of each, there's a huge variation as Awesomeness pointed out. The mileage will vary considerably by driver too.

Maybe the important issue for you, rockDAWG, is that we compared the amount of Diesel needed at every stop. We drove same speed, same route, same hills, same temperatures, etc and the M-1078 used just about half the fuel that the M-1083 used. I am guessing I averaged about 6 mpg. That was with 3.90 gearing.

Since then I upgraded to 3.07 ratio and bumped mileage by a mpg or so. Personal best on the highway, 3.07 ratio, on a long drive is now 8.5 mpg with GPS route mileage and actual pump gallons on two consecutive fillups.
 

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Kbarnes0

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Tacoma WA
Stock M1090 dump truck. No long term logs yet. I should have topped off before I left. Truck had an eighth of a tank consumed during shop time, fluid changes and repairs.

Truck scale weight with full tank and driver, co-driver. (no doors 🤔)
24,500#

Did 173 highway miles, 87 ish empty, and 86 ish loaded with 15-18 thousand pounds.

With the hammer down 99% of the time it calculated out to be 5.2 Mpg.
 

CRayGill

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Cherryville, Oregon
I have long term gas receipts for my 1998 1083/88 conversion (The Sloth):
3,000 miles average: 5.5mpg

Empty vs 2015 RZR 1000 (1,700# all in) on the bed with 2017 38' bumper pull Cougar travel trailer (~10,000#) on the ball:
Perhaps .5 mpg difference

We live in the foothills of Mt. Hood, Oregon. We are going up and down hills from the time we hit the starter until we turn the power off.
 

CRayGill

New member
12
6
3
Location
Cherryville, Oregon
I have long term gas receipts for my 1998 1083/88 conversion (The Sloth):
3,000 miles average: 5.5mpg

Empty vs 2015 RZR 1000 (1,700# all in) on the bed with 2017 38' bumper pull Cougar travel trailer (~10,000#) on the ball:
Perhaps .5 mpg difference

We live in the foothills of Mt. Hood, Oregon. We are going up and down hills from the time we hit the starter until we turn the power off.
 

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