GM Mileage 6.6 gas & Diesel

[Jayco23FB]

Looking to get real world towing fuel mileages while towing a 6,000lb travel trailer. I would love to hear from anyone towing that size trailer with a late model GM 6.6 gas or 6.6 diesel as well any comments pro or con on either. (I would also be interested hearing on comparable Ford or Ram rigs towing same) Plan to purchase a new 3/4 ton when they become more available. Thank you.

[BackOfThePack]

At the sane speed and at the same weight (loaded for camping) a travel trailer exerts a 40-50% penalty at approx 60-mph. Size & Weight don’t mean much compared to the aerodynamic problem.


1972 or 2022 changes nothing.


If the tow vehicle (with scaled weights) over the same road course at the same speed gets 16-mpg solo, it’ll see 7.8-9.6/mpg while towing. (Take that to the bank).

An aero TT with details worked will stay under 40%. A box TT (slides, etc) with typically sloppy hitch rigging can (will) exceed 50%.

If it matters then SAFETY LONGEVITY RELIABILITY ECONOMY will be given the attention they deserve. They track together 90% of the way.

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[BackOfThePack]

valhalla360 wrote:

BackOfThePack wrote:
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.

There are some wacky numbers on this thread.
- 2mpg...maybe if you are climbing an 8% grade and try to keep up at 75mph...but over 50-100miles, it would be almost unheard of and in mountains, there is typically a downhill to go with every uphill.
- Diesel typically get's 20-40% better MPG (and 40% is unuusal). 52% improvement strains credibility.

For general planning purposes, figure somewhere on the order of 7-12mpg.

Biggest issue is driving style.
- Slow down a bit often will generate significant MPG improvements.
- If in hilly, let gravity speed you up on the downhill and then let a little speed bleed off on the uphill (assuming you aren't in a congested area disrupting traffic).
- Doesn't work for weekenders (or if you have a weeks vacation) but we've actually changed travel days based on wind projections. Going from a 30mph headwind to a 10mph tailwind has a pretty massive impact. At 60mph, the engine feels 90mph vs 50mph loads, since the bulk of the power is fighting wind resistance.

At $4.25/gl diesel, a diesel pickup getting 16-mpg is the same mpg COST as a gasser at 10.5/mpg where the energetic content is reflected by price (BEFORE the price of the Diesel engine option).

There’s no reduction in EXPENSE PER MILE until fuel prices are normalized and extra-cost engine is figured. (Write a business plan).

A diesel IS NOT a more economical engine to operate for Joe Sixpack. That disappeared in 2007 until which time diesel was CHEAPER per gallon.

[BackOfThePack]

Grit dog wrote:

BackOfThePack wrote:
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.

And yet where you live the 2 fuels are about the same price. And generally are within about 10% of each other everywhere, not the 50% difference to embellish your point.

At THAT price the MPG is equal.

[valhalla360]

BackOfThePack wrote:
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.

There are some wacky numbers on this thread.
- 2mpg...maybe if you are climbing an 8% grade and try to keep up at 75mph...but over 50-100miles, it would be almost unheard of and in mountains, there is typically a downhill to go with every uphill.
- Diesel typically get's 20-40% better MPG (and 40% is unuusal). 52% improvement strains credibility.

For general planning purposes, figure somewhere on the order of 7-12mpg.

Biggest issue is driving style.
- Slow down a bit often will generate significant MPG improvements.
- If in hilly, let gravity speed you up on the downhill and then let a little speed bleed off on the uphill (assuming you aren't in a congested area disrupting traffic).
- Doesn't work for weekenders (or if you have a weeks vacation) but we've actually changed travel days based on wind projections. Going from a 30mph headwind to a 10mph tailwind has a pretty massive impact. At 60mph, the engine feels 90mph vs 50mph loads, since the bulk of the power is fighting wind resistance.

[Thermoguy]

I have a 2500 Duramax. 2 Trailers, one gooseneck an one 5th wheel rv. The 5th wheel is larger and a much bigger box. The gas millage is consistent about 13 towing and 18-20 not towing - freeway. Previous to this I had 2 gas vehicles. Neither got the gas millage the Duramax gets. As for maintenance, the Duramax is less maintenance, but more expensive if something goes wrong. We get free oil changes at the dealer, so that is a great benefit with many dealers these days. No experience with the 6.2 gas.

Also, currently in Western WA, Diesel is almost $1.00 more per gallon over gas. There is no reason for that, Diesel should be cheaper.

Get what gets the job done the best and has your future in mind. If you buy for todays gas prices, you will be looking for something else when gas prices normalize.

On edit - you mention you plan to get a 3/4 ton when they become more readily available - so your a few years out...

[Grit_dog]

BackOfThePack wrote:
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.

And yet where you live the 2 fuels are about the same price. And generally are within about 10% of each other everywhere, not the 50% difference to embellish your point.

[trail-explorer]

At least 5 years ago I started putting money into an extra bank account I have.
I've turned that money into my "camping and recreation fund" savings account.
The money from that account goes towards fuel for my vacations and camping trips.

Because that money sits there and isn't used for anything else, it's not a huge hit to my main bank account to go camping.

[deltabravo]

DITTO.

The tow vehicle is a tool that has a job to do. Let it do its job and don't be concerned with what it costs to get the job done.

I've had a 2008 Duramax since the truck was new. I've hauled 3 TTs and two truck campers with it.

MPG runs 10.5-12 hand calculated.

[LVJJJ]

When you start worrying about gas mileage, you are no longer having fun RV'ing. Just drive it and enjoy.

[ktmrfs]

depends on where you live I guess. Here diesel has been within $0.10/gallon of 87 octane gas for the last 15 years or so. Occasionally it will be cheaper, occasionally $0.20 gallon more, but usually within $0.10. My experience in Mt, Id, WA, Or at least.

As for mileage can't comment on the 6.6 Gas, but our 2015 duramax gets 10-12 towing our 35ft TT, long flat freeway I can get 12, Rocky mountains in the 9-10 range. we usually tow at 65 on the freeway (except CA) and 55-60 on backroad highways. Non towing is where the Duramax really does well. We consistently get 18-20 hand calculated traveling between OR and central MT running the speed limit + 5 or so. MT and Idaho has lots of freeway with 75 and 80mph speed limits.

When picking and choosing between gas and diesel, economy really didn't play into my decision, it was which engine would I like driving the best when towing and empty.

[BackOfThePack]

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.

[Dadoffourgirls]

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.

[Sjm9911]

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]

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.