Excessive fuel consumption while towing?

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RamMike7

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I got to tow with my new 6.4 Hemi for the first time, now granted this is the first hemi i have owned since i have always purchased cummins power plants. Anyhow, my 1st trip with our 30' 9500lb. 5th wheel traveling here in Missouri with mostly flat with a few rolling hills and keeping my speed around 62 mph netted me a whopping 6.3 mpg! If we go out west with this thing im afraid to even guess how bad it might be. I expected the Hemi to not do as well as the cummins, but not quite this bad. As far as power, im actually impressed with the hemi's performance with the 8 speed, but 6mpg towing is a shocker to me, and my wife is giving me hell about it also. Could there be something wrong with the truck?
 

crash68

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Probably nothing wrong with the truck other than what you pointed out it has spark plugs.
Wind resistance is a major contributor to fuel economy or the lack there of, if your towing a fiver you have a nice big sail above the cab catching air.
Use the Tow/Haul mode and let transmission do its job. It's recommended to use 89 octane, which you'll want to use while towing. The higher octane will help keep the engine from pulling timing under load.
Keep in mind your towing with a gasser expect the rpms to rev high to get to the torque band. The 6.4 can stay at 4K rpms all day long without issue.
 

ChesterJack

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My 2020 1500 hemi has similar very poor gas mileage while towing travel trailer. I upgraded to 2021 2500 Cummins a month ago and am getting double the miles (12-15MPG) per gallon with the diesel.
 

Firebird

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Seems low to me. I tow 9000 pounds and usually get 8.5 to 9 mpg depending on terrain, 4.10 gears too. However, I do live in Florida, so I don't have monster hills to pull
 

tjfdesmo

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My 2015 2500 with 6.4, 6 speed, and 4.10s would average 7.5-8.5 pulling a 41' toy hauler that went across the scales at 23,160 combined. My 2019 3500 Cummins HO got 9-10 pulling the same trailer.
 

PoMansRam

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How many more MPGs did your cummins powered trucks get?

Considering other costs associated with owning a diesel, such as higher cost per gallon for fuel, are you really loosing money with the new 6.4L hemi?
 
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RamMike7

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Seems low to me. I tow 9000 pounds and usually get 8.5 to 9 mpg depending on terrain, 4.10 gears too. However, I do live in Florida, so I don't have monster hills to pull
Yeah, i dont think something is right, but dont know what to tell the dealer as far as checking for anything specific. If timeing or something were out of spec, there should be a code thrown.
 

Aces4ACE

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What ever you do, don't try to save gas when towing. Especially with a gas engine. If you attempt to keep the RPM's down, it will only be additional strain to the engine and transmission. Higher RPMs should be the normal for towing.
 

dhay13

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Agree with many here that is low. My son towed his 8100lb 32' (overall length) TT all over the country and averaged about 8.0 hand calculated in his 2018 2500 6.4 4.10's. I have t e same identical truck and towed my step-sons 9300lb 36' (overall length) TT on pretty flat ground and got 7.4 hand calculated and we were doing closer to 65-75 MPH
 

NH RAM

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You're considerably lower than you should be. How many miles are on the truck?
I pull my 5w that's probably about 10,000-10,500 loaded (gvwr 11k) with 34" tires and got 9.2 on my last trip of 5 hours at 64 mph. Towing my 7500# travel trailer I got about 8.8-9 mpg- in the flat states I got 10mpg.
 
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RamMike7

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You're considerably lower than you should be. How many miles are on the truck?
I pull my 5w that's probably about 10,000-10,500 loaded (gvwr 11k) with 34" tires and got 9.2 on my last trip of 5 hours at 64 mph. Towing my 7500# travel trailer I got about 8.8-9 mpg- in the flat states I got 10mpg.
I have 1400 miles on the truck. Everything is stock.
 

SniperDroid

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I think the mileage is OK for the Load your towing. Everyone's driving habits are different, and I don't think I can gauge my mileage against someone else's. I pull about 7500 pounds with the 6.4, and I get 8.4 to 8.9 depending on where we travel. Better than I got with the old 2005 ford 5.4L we started out with, but less than the 6.0L Diesel I had for two years. The Diesel also broke my back with all the expensive maintenance. Ill stay with gasoline engines for now. Were considering buying a Drive-able camper and it will be a slightly used Ford V10 if I do. I'll put up with less gas mileage for a little less maintenance headaches.

You also have to consider the mechanics of the two engines. The gasoline engine does not reach it maximum power until higher up in the RPM's, around 3500 to 5000 depending on the engine. The diesel hits full power around 2000 to 2500. Makes and easier and less thirsty tow down the road. Espically when the trailer your towing is 150% of your tow vehicle weight.

Safe Travels...
 

dhay13

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Just to add...I towed that same 8100lb TT with my 2013 1500 5.7 3.55's and only got about 6.5 MPG towing it so got about 1.5 better with the 2500 6.4 but unloaded I got 2 MPG better with the 1500 5.7 (12.2 vs 14.4-all hand calculated)
 

tron67j

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Has already stated above, you can't really take anybody else's numbers and compare them to yours to obtain any useful data. You have just too many variables that will impact your miles per gallon calculation. Wind resistance, actual grade of road, exact miles per hour driven at any one time, exact weight of tow vehicle and trailer, how the weight is distributed and if there's a lot of liquid weight that sloshes around and impacts mileage, are the wheels on the trailer true in line and bearings properly greased, and a whole host of other things. Before spending a lot of effort chasing what somebody else reports, you should first start by doing all of the things that you can do on your own such as verifying weights and distribution, removing water and waste water from the vehicle, check that all trailer wheels are aligned properly and greased, and anything else that could be impacting the towability. Meanwhile you can also have the dealership check out the truck to make sure there isn't anything wrong. But at the end of the day your numbers are going to be your numbers based on what, how, and where you tow.
 

SKS 800

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Like stated, depending on driving conditions it doesn’t seem out of line. I just finished a 2 week, 1500 mile trip around Lake MI. I have a 33’ fifth wheel and my worst tank was 6.6 mpg. That’s on a 2021 3500.
 

18MegaRam

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I tow a 20k lb fifth wheel with the Cummins, and get about 12-13 mpg. Maybe 10. I don't really pay attention to it. You won't like it if you come out West. Gas in California is $4.50 - $5.00 per gallon. Diesel is cheaper than gas again. The neighboring States are about $1 less per gallon.
 

18MegaRam

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How many more MPGs did your cummins powered trucks get?

Considering other costs associated with owning a diesel, such as higher cost per gallon for fuel, are you really loosing money with the new 6.4L hemi?
Diesel is cheaper than gas here in CA.
 

68PowerWagon

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Yeah, i dont think something is right, but dont know what to tell the dealer as far as checking for anything specific. If timeing or something were out of spec, there should be a code thrown.
That does seem low. Is it broke in yet? I have a 13k 5vr & I get 8-10 depending which way wind blows! :D I admit my truck is a 16' with the old 6 speed, which I would think would be less of an advantage no matter how you look at it. I have also re-geared, so I have 4.56. Pulls great for a gasser!
 
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RamMike7

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That does seem low. Is it broke in yet? I have a 13k 5vr & I get 8-10 depending which way wind blows! :D I admit my truck is a 16' with the old 6 speed, which I would think would be less of an advantage no matter how you look at it. I have also re-geared, so I have 4.56. Pulls great for a gasser!
Its probably not broken in yet as it only has about 2500 miles on it. But i have seen others say they didnt see a huge change after break in.
 

pjtj2k

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I have 2500 6.4 w/ 4.10. Just wrapped up 7500 mile trip. Our milage was anywhere between 9.5 and 11.4. Most of the time we sat right at 10mpg. Trailer was 6.5k, and a mix between flat and mountains. Yes, head winds will cause your milage to drop. Best thing to do there is find a 18 wheeler and tuck up behind em.
 
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