Total shot in the dark here but 15mpg seems high assuming it is a fairly normally tall cargo trailer, since wind resistance kills mpg much more than weight, and assuming your trip has decent elevation change given the states. I would ballpark more like 12-13, but again this is a guess.

 

guesses are fine. Thank you!

 

Add me to the 12 mpg tally

 

Depending on your speed and if that cargo trailer is enclosed. If you're on west side and have to come over the mountains, assuming I90, I would say 10-12mpg, perhaps better. You'll have a regen or 2 in the mix probably also.

 

I'm getting 12-13 pulling my camper, much better then the 6mpg I was getting on a good day with the gasser. If you are pulling something without high profile I bet you could get near that 15mpg mark.

 

I have basically the same truck and I get about 18 unloaded on highway (although I run heavy and have heavy wheels/tires) and 7-9 MPG highway with my 19k fifth wheel (13'4" tall and 100" wide). With my old travel trailer (about 10k lbs, 11' tall, 96" wide) I got around 10 MPG highway. With my 28-foot enclosed cargo trailer (about 8' tall, 102" wide) I think I'm at about 11 MPG. So depending on the dimensions of your trailer (frontal area is far more important than the weight with regard to highway fuel economy) I'd say 11-13 is about where you'll end up.

 

Don't want to be negative Nellie but I think 15 mpg is quite optimistic. I don't have even close to the same truck but I get about 13 mpg towing my cargo trailer on the highway on flat ground. Trailer is 16' x 7' x 7' tandem with 7,000 GVWR

That 13 mpg is with maybe a 3k -4k lb load in the trailer. That's also at 70 mph on the interstate. I'm not sure whether an L5P would do about same, better or worse but reasonably sure it's not going to do 2 mpg better. I'd say plan for 13 and hope for 14. If you get 15, jump for joy!!!

 

Based on my old truck (2017 SRW 3500) and my old trailer which weighed in around 6000 lbs, I would see 13 mpg pulling about 600 miles through the Rocky Mountains. Same trip, same trailer when I had a 5.7 hemi I would get ~8.5 mpg....

 

I had a 26 ft. TT that weighed about 7K & would get 12-13 with my LB7 10.5 when I towed a 14K 5th wheel.

 

Rule of thumb, shot for 10mpg and hope for higher. Better the be happily surprised, than negativity surprised.

 

I have pulled this trailer twice now and averaged 14mpg and 10 mpg respectively. (The 10 mpg was almost all uphill) both trips were relatively short.

I am leaning towards assuming a 15 mpg average, (95% highway) but wanted to double check real world feedback.

Curious why if you already have data points at 10 and 14, why you would assume 15? I'd probably assume 12.

 

10 and 14 were short trips with little highway. I assumed highway towing would get better mpg.

Seems like the consensus is in the 10-13 range. Im glad I asked so I get reimbursed correctly.

 

Trailer profile, weight and speed all contribute to fuel economy.

With my LMM towing a 17k 5vr I get 10 MPG towing at 65 MPH. Towing at 70 MPH I get 8 MPG.

With the L5P towing an equipment trailer with tractor and implements at 8k best that I could do was 14 MPG at 70 MPH.

 

9mpg… including hill climbs.

we towed 63mph average… 40mph headwinds… so, off the truck nose, and wind noise in cab, sometimes over 100mph airspeed. Hills in Texas…10k trailer and accessories.. 10MPG

 

So far with the new 5er, <15000 lbs and 13.5", I'm averaging 9.2 mpg. That's with under 900 miles towing it. The TT before was around 10.4, but had a much shorter and lighter profile.

 

Taking that drive across eastern washington - as soon as you get past ellensburg on i-90 you can have winds that will either help you or hurt you. (it gets worse at vantage) Note that a side-wind kills aerodynamics too (not just a headwind).

I drove from fargo nd. through spokane and on to portland, oregon with a nasty headwind. It wasn't pretty on the mpg when I started heading southwest from spokane. I was filling up often and I vaguely recall getting less than 10mpg. 40 mph headwind.

I was towing a 6 X 10 wells cargo enclosed trailer that was empty.

I would guess at 13 mpg and the saying "your mileage may vary" definitely applies.

The slower you drive, the better it will be (obviously)...

jeff

 

OP… Where in the Gem State are you traveling to?

 

BSA Camp Easton on Couer d'Alene

 

definitely closer to 12mpg average. Just finished trip with 3500lb aluminum boat from ID to TX and back. At 65-70mph driving like a granny and zero throttle-happy events, 14mpg. Over 80mph coming back and not caring much about mpg's with lots of whiskey-throttle events, 11mpg. Averages hand-calculated at each fillup.

 

Depending on how fast you drive, 9 mpg on the low side, 13 mpg on the high side. I stay at 65 mph when towing our 25 ft TT. I get 12-14 mpg. If I go faster or push hard, I get closer to 10 mpg. At 65 mph, it takes 5 - 10 minutes longer to your destination but you get it back in better mpg numbers.

 

Not knowing what kind of trailer you have, if it's more rounded or just a box on wheels, and what speed do you like to drive, it's very hard to say. My first fifth wheel which was a low profile, only 10 ft to the top of the air conditioner, but very Square and, for its length, fairly heavy, I got around 10 miles per gallon, on average. It grossed 11,360 lb. My current fifth wheel, which is a fair bit more aerodynamic only grosses 10,500 lb, is 3 ft longer, and almost 3 ft taller, and I normally get between 11 and 12 and 1/2 Mi per gallon, depending on my speed. I did find that with my old rig, if I slow down from 65 to 60 with my old O2 duramax, I picked up about one and a half miles per gallon. With my current fifth wheel and the same 02 duramax, I was averaging about 11:00 to 11 and a half with my current 2017 fifth wheel. I've towed my current fifth wheel with my 2022 3500 Duramax and I averaged, not surprisingly, just about the same, 11 to 12 miles per gallon. I have been Towing closer to 65 then the 60 to 62 mph that I used to tow with my 02, which seem to be a bit of a sweet spot, and I'm getting the same mileage with nearly 200 more horsepower. Speed and aerodynamics are the key. I can guarantee that you will get better mileage if you slow down. If you regularly travel around 65 mph, that's about as good as closest you can get to most duramax's sweet spots. YMMV...literally. 😁

Lyle

 

This is my setup, total weight was right at 32k lbs on the way south and 27k going north. I went from Alaska to WV, to NC, up to Maine and then back to Alaska. Running 65mph, I averaged 10.2mpg over the 12,000 mile trip. You should get somewhere between 12-13 if you can keep the speed down.

 

View attachment 1133421
This is my setup, total weight was right at 32k lbs on the way south and 27k going north. I went from Alaska to WV, to NC, up to Maine and then back to Alaska. Running 65mph, I averaged 10.2mpg over the 12,000 mile trip. You should get somewhere between 12-13 if you can keep the speed down.

That's impressive for that much load!

 

I pull a 44 ft. toyhauler. I had my truck and rv on a CAT scale and I’m at 30,300. If I get 9 mpg on avg I’m happy.

 

13.4 mpg towing our 23 foot travel trailer, 2022 Wildwood ultra light.
18.3 mpg towing our 19 foot bow rider boat, 2003 Four Winns 19 Horizon.
We tow each 150 miles one way to the lake, where it is stored until the fall when we tow them back home and put them away for the winter.
Through Lexington KY and into Eastern KY, so no really flat highway.
Boat tows at 70 easily, camper tows from 65 to 70 easily. Our 2022 3.0 has plenty of torque and the engine never got above 2,000 rpm.
Get around 26 mpg unloaded driving back and running around 80-85 mph.

 

12mpg pulling an empty 4500# dump trailer (24" sides, extended height front, very flat front).

 

This was pulling a 10,000# travel trailer through the mountains in BC (Calgary to 100 Mile House and back)

 

Update: we ended up taking the trip without bringing the trailer. I averaged about 21 MPG round trip.