GM Mileage 6.6 gas & Diesel

I've had three Chevy Duramax Diesel Duallies, 2005, 2011, & 2018. The 2005 pulled two TT, a 24', then a 30', then a 35' Fifthwheel. Saw very little mileage difference between them. The 2011 pulled the 35' 5er, then a 40' 5er then a 43' 5er. Again very little difference in mileage. The 2018 has only pulled the 43', but mileage is still pretty much the same with all combinations, leading to my thinking that it's the big square box behind that effects the mileage much more than the weight, since the 24' TT was probably less than 5000 Lbs while the 43' 5er is close to 20K Lbs. Overall with all three TVs and the different RVs typical mileage is 9.5 to 11 depending on conditions.
Your experience may differ, but that's what I've come up with in over 100K miles and 12 years towing.

Im going to go here again, you can look up previous posts. 9 to 14 towing depending on speed and terrain. Around 13 at say 60 mph, 65 to 75 will be 10 to 12 or a bit more. I usally will go faster. I think I got 13 avrage to disney from nj at like 65 mph. 13 to 16 not towing on the same principle. I get 15 ish at 65-70. And 14 to 13 at say 80. I have 26000 miles on my 2020 2500 double cab? With reguler bed lt 4x4. Half of that or more towing. TT is about the same weight. I do load up the bed with lots of junk and use the bed outlet while towing. Pros, bigger gas tank, less stops. Trips that I had to stop 3 times for fule with the 1500 can be made on one fill up. This is because larger fule capacity and a little better fuel economy on the newer truck. Not much difference in towing vs not towing with a 5500 lb TT. Maybe 1 to 2 mpg less.

Duramax?

Michelle.S wrote:
I've had three Chevy Duramax Diesel Duallies, 2005, 2011, & 2018. The 2005 pulled two TT, a 24', then a 30', then a 35' Fifthwheel. Saw very little mileage difference between them. The 2011 pulled the 35' 5er, then a 40' 5er then a 43' 5er. Again very little difference in mileage. The 2018 has only pulled the 43', but mileage is still pretty much the same with all combinations, leading to my thinking that it's the big square box behind that effects the mileage much more than the weight, since the 24' TT was probably less than 5000 Lbs while the 43' 5er is close to 20K Lbs. Overall with all three TVs and the different RVs typical mileage is 9.5 to 11 depending on conditions.
Your experience may differ, but that's what I've come up with in over 100K miles and 12 years towing.

This is interesting...makes sense. Thank you

GM 6.0 gas towing a TT with GVWR of 7400. anywhere between 2 mpg (hilly and mountainous terrain) to 9mpg flat highway a @ 60-65 while getting passed by every other vehicle on the highway. I once seen 15 mpg on flat highway not towing on a trip through OH/IN lol. Fill up with $4 a gallon, soon to be $5 gas, and have at it. You'll feel better if you forget about the fuel mileage. The oil burners I had did not fair much better if at all towing. I suspect the 6.6 gas would be the same as the 6.0 or slightly thirstier.

I have a 2020 Chevy 2500 with the 6.6 gas. Towing 8400 lbs I am getting 6 to 9 mpg depending on terrain and wind. Head wind is a killer on mpg. Non towing it will get 20 mpg on flat ground, no wind, cruise control, an under 60 mph. Normal interstate at 70 will get 18. About 2 mpg less than my 2016 1500 with a 5.3 which I didn’t tow with. This is towing a toy hauler that is 12 foot 6 inches tall.

OP, great question, but at the end of the responses, you won’t have any succinct info anyways. There are just too many variables, not the least of which is the owners “perception” of their mileage.
Factor in everything else to make your decision, imo. Diesel will be about what is expected at 20-30% better mileage if comparing apples to apples.

Jayco23FB wrote:

Sjm9911 wrote:
Im going to go here again, you can look up previous posts. 9 to 14 towing depending on speed and terrain. Around 13 at say 60 mph, 65 to 75 will be 10 to 12 or a bit more. I usally will go faster. I think I got 13 avrage to disney from nj at like 65 mph. 13 to 16 not towing on the same principle. I get 15 ish at 65-70. And 14 to 13 at say 80. I have 26000 miles on my 2020 2500 double cab? With reguler bed lt 4x4. Half of that or more towing. TT is about the same weight. I do load up the bed with lots of junk and use the bed outlet while towing. Pros, bigger gas tank, less stops. Trips that I had to stop 3 times for fule with the 1500 can be made on one fill up. This is because larger fule capacity and a little better fuel economy on the newer truck. Not much difference in towing vs not towing with a 5500 lb TT. Maybe 1 to 2 mpg less.

Duramax?

6.6 gasoline single rear axel.

Grit dog wrote:
OP, great question, but at the end of the responses, you won’t have any succinct info anyways. There are just too many variables, not the least of which is the owners “perception” of their mileage.
Factor in everything else to make your decision, imo. Diesel will be about what is expected at 20-30% better mileage if comparing apples to apples.

If gas is getting 8 mpg, 25% better is 10mpg. I got 9.9 in 2020 hauling my trailer to/from Kansas with a CC Dually Dmax.

I got 9 in 2021 hauling my trailer to/from Iowa with a Express 6.0. I stayed off the interstate on the trip home. I added a wind deflector (that was a $20 used purchase) that seemed to help.

When diesel costs $4.25/gl and gasoline runs $2.80/gl the fuel economy is the same.

16-mpg diesel and 10.5-mpg gasser.

1). Figure miles owned in advance. Add diesel premium to needed differential (and insurance plus maintenance, etc).


Diesel equivalent hasn’t been cheaper since 2007.