MPG/Broken Record

[Russ Knight]

I've searched the forum with not much luck and I'm sure this has been discussed ad nauseum. I understand the fuel economy is never going to be good in a 5 ton. What spring / governor combination will give the best results in fuel economy? Will advancing the timing help? Straight pipe? I checked mine yesterday and it's 5.17 around town.

Thanks,

Russ

 

[doghead]

That's great, be happy with it.

 

[Russ Knight]

Thanks for helping with the title too.

 

[papabear]

I would think anything 5MPG and above is very good!!

 

[CMPPhil]

5 MPG loaded or empty?

Hi Russ

Fuel economy is an intersting topic be it a 5 ton or Jeep, a lot of it is the vehicle, a lot of it is the driver. I assume your 5 MPG is running empty, can't help wonder what the same truck, running the same route would get running fully loaded?

The another assumption I'm making is that you are running straight pump diesel fuel not some blend of McDonald's fry oil and Swiss watch oil. How different is pump diesel today from the fuel these engines designed for?

My fuel mileage varies greatly, driving my 3 ton gas truck effected by many things. Driving alone in a hurry is the worst down to 4-5 MPG my best fuel economy comes running in a Convoy where I have often gotten better than 10 MPG.

Cheers Phil

 

[Jbulach]

Isn’t this a ROPS truck, don’t they have an electronic motor and 7 speed trans? If so nothing comparable, likely has been discussed that much...

 

[M35A2-AZ]

I just finished part of the MVPA Rt. 66 convoy in my M923A1 pulling a M105. Had a S280 shalter in the M923A1 and all types of spare tires and parts in the M105 and tools. I drove a total of 3110 Miles and got avg. of 8.5mpg. On the convoy we drove around 30-35 mph, on the way to the meet up and the way home from the convoy I drove 55 mph.

 

[Tinstar]

Maybe run some sea-foam injector cleaner and two-cycle oil added to tank.
That’s my combo and I get a solid 10 mpg all day long.
When I have 6-8 tons of gravel in back it’s about 7-8 mpg.

I don’t drive over 55.
In my 5 ton that’s fast enough for me.

 

[Russ Knight]

Maybe run some sea-foam injector cleaner and two-cycle oil added to tank.
That’s my combo and I get a solid 10 mpg all day long.
When I have 6-8 tons of gravel in back it’s about 7-8 mpg.

I don’t drive over 55.
In my 5 ton that’s fast enough for me.

Is that highway or combined?

 

[Russ Knight]

Isn’t this a ROPS truck, don’t they have an electronic motor and 7 speed trans? If so nothing comparable, likely has been discussed that much...

No, mechanical injection and same Allison as far as I know.

 

[simp5782]

You will have worse mileage around town and on highway without 2000lbs in the bed maybe even 3k. It will put the tires down giving more torque contact and less throttle needed. My mpg is better with the bed loaded to the hilt with tires than without.

Average mpg towing i was seeing with the allison was 5.5 in an A1 truck. This is 50 to 60k pounds over all types of terrain. Now i see 6. Most A2s can see upwards of 10 at 55/58 convoy speeds on flat ground.

Other factors you have to consider are idle time. Your truck should idle for 20 min if not more. Especially before you first drive it. Not just hop in and go. Plus a 5min idle time before shut down. My truck idles for 30 to 40mins before i start any of my road trips so i probably burn gallons of diesel or so with just that.

This time of year is winter blend fuel which is always worse. I dont know if florida gets it but never know.

Getting the engine properly tuned and in sync with the transmission is important for performance. Ron may chime in here on this as some trucks were tuned by units and perform differently than others. Im talking about an A2 walking off and leaving another A2 by nothing more than a modulator adjustment and properly metered pump for fuel/altitude.

Give her more air. Do the air cleaner mod, or a TMG air cleaner mod or fab up a ram air system. That helps alot.

ROPS trucks are just a 5ton with a cage and different dash display and more room actually it seems.

Just my .02


I will add that I have desplined front flanges so that is a better mpg factor as well.

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[red]

Your right foot will be the biggest factor. In my m816 usually get 6-6.5mpg with a mix of city and highway at 55mph (2000rpm on 395's). Best I've gotten was 7mpg on a trip at roughly 50mph (1900rpm).

Stock exhaust, donaldson intake snorkle, and the smaller diameter air filter from those military guys.

Opening up the exhaust to a 5" should help. Wrecker beds are listed at 17k pounds so always running around at loaded weight.



Forgot to add, front axle has been plumbed for disconnect.

 

[Evil Dr. Porkchop]

You will have worse mileage around town and on highway without 2000lbs in the bed maybe even 3k. It will put the tires down giving more torque contact and less throttle needed. My mpg is better with the bed loaded to the hilt with tires than without.

How much better is your MPG with a load of tires than empty? I would have figured all that extra weight would lower the fuel mileage, unless your trip was all downhill. I googled torque contact and such but didn't find any real info, could you expand on that a bit? Thanks.

 

[swbradley1]

No, mechanical injection and same Allison as far as I know.

They also put an Allison push button transmission in them as well.

 

[simp5782]

How much better is your MPG with a load of tires than empty? I would have figured all that extra weight would lower the fuel mileage, unless your trip was all downhill. I googled torque contact and such but didn't find any real info, could you expand on that a bit? Thanks.

Well i run wrecker springs on my truck so it needs weight to put pressure on the tires to put em down on the ground more. My mpg loaded with just the truck is 9 with my current setup running 68 at 2850rpms. Steady.

With the bed weight you do not have the front tandem wheel hop either. It keeps that bounce down.

Im comparison. I left the GA rally empty with only a spare tire. I burned 35 gallons of diesel over the 310 mile trip and took right at 5 hours. I left the yard in Cookeville going back to the rally with a full bed load and a mep003a/116a3 in tow. To the fuel station in Chattanooga i burned a little over 12 gallons thru the 110mi hike on mountain roads and steep climbs. I fueled up in Cookeville and again in Chattanooga since it was cheaper than GA. So about 9mpg loaded and empty.

From my door to the edge of nashville is 183miles exactly. Just an empty truck with my current setup it takes me 2hrs 40mins to cross that span. Just over 1.15mi a minute. Over the same span carrying 10 tires in the bed and a LME tent setup i ran it in 2hrs 28mins. Averaging 1.23 mi per minute. This is non stop over night driving with no traffic. Same outside conditions nearly.

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[98G]

5MPG is low for an A2. Around town empty, I typically see 9mpg out of A2s. Highway speeds cruising empty I've seen an honest 12mpg. The worst mileage I've seen from an A2 was flat towing an M109A3, and I averaged 7mpg between northern OH and Waco TX. These numbers are from multiple different trucks, and hAve a sample size of about 30,000 miles.

A0/A1 trucks have less variability. With them, it's usually 5-6mpg loaded or empty, or even towing another loaded truck. These numbers come from multiple trips of 1500miles or so with many different trucks.

My M818 with the turbo gets almost 8mpg empty, and got about the same while towing an XM818.

I would be concerned about an A2 getting 5mpg. Something isn't right, as that is an outlier.

 

[Karl kostman]

Russ I sure as heck do not mean to trivialize what your looking for but like was said in the above posts I think you truck is doing very good and if you going to improve on what your getting now, what is that going to take, is it possible, what are your actual gains going to be? If you spend 4K$ trying to make this truck into a toyota hybred I would estimate that the gains will actually break even on the 3rd owner of this truck after YOU! It is what it is and remember you NOT starting out with a 3000 pound car!
KK

 

[M543A2]

When I have a vehicle that does what I want it to, I do not look at fuel mileage that much. On our M series trucks we disable the front rear axle by removing one axle shaft and substituting an axle cut off about 4" from the tulip end. This disables the axle but does not damage it. The gears inside turn normally even if the one shaft is not connected to the diff. Remember how, in a tandem civilian truck with power divider lock there is a sign on the dash that says the lock is not to be used on dry roads, so why do it with our trucks? Also, you would not dare run your 4x4 truck in lock on dry roads. We find the truck runs much more freely on the road this way, especially the wrecker which is heavy and dump truck when loaded. Tire wear and differential temperature is also reduced because when the axles are locked together the different wheel sets fight each other because you never will see the same tire outside circumference on all wheel sets unless you have them carefully measured and matched all around. Good luck with that! This fighting each other eats up power and reduces fuel mileage, not to mention tire wear accelerated. When we are going into challenging conditions we put the complete axle back in. I see some axle shafts "de-splined" offered but we have never had a problem in many miles of driving with the cut off axle. The spider gears stay in place OK without the axle in place. When removing the full axle or the modified cap we place a can under the hub to catch the small amount of gear oil that will come out. After several changes we check the diff oil level. You can make quite a few changes before having to worry about oil level. We have a four-way lug wrench in the cab to make the changes with. We find that the truck will have better traction on the rear if we disable the front axle, not the rear one. It must have to do with the leverages of the link system locating the axles.

 

[swiss]

I like when I run the M62 Gasser Wrecker and get 3.26 miles per gallon! That was a good day running down to the GA Rally a few years ago.

 

[lindsey97]

With my (3) M923 A0/A1/A3 trucks, I get 7 mpg consistently, unloaded just cruising around and interstate driving. I want to try a set of manual lockup hubs one day, to see if that will improve mileage.