BIL not happy with 2021 Silverado 2500HD 6.6 gas

Azjeff

Active member
My sister and BIL just retired, both in early 60s, both from gubmint jobs. Their camping up til now has been going to a local state park 2-3 times a year with the '70s Coleman pop-up that his mom bought new . They've done motel travelling (live in Pa) to New England, Florida, and a cruise trip to Alaska. They decided they want to travel around so last summer ordered a new 2500HD LTZ and a new Jayco 32' 5th wheel, GVWR 10-11k. They got the truck in October and the trailer finally came in in January so it sat in storage until April. They've taken 2 trips so far, the longest being about 40 miles one way to a state park. Just found out BIL is so disgusted with the gas mileage he won't even say what it is. I don't know what he expected but I know he thought he'd get better mileage with that 5er that I'd get with the 6500 lb trailer because the salesman told him air flows up over the cab then over the 5er better than a trailer. I asked him how fast he was towing and he said with traffic, which in Pa on I-80 means 75. He's a bit of a know-it-all so I'm not even going to suggest trying 65. He didn't want a Duramax because he didn't want to deal with the diesel. Hope they didn't make an expensive mistake.

I don't know what we'll get yet, hopefully getting our first trip out with this truck this weekend if the monsoon weather lets up. I don't expect 10 mpg, will be happy in the 9s. I'll run 65 on the highway and slower on any decent grade.
 

Wayne

Administrator
Staff member
I don't know what he expected but I know he thought he'd get better mileage with that 5er that I'd get with the 6500 lb trailer because the salesman told him air flows up over the cab then over the 5er better than a trailer.
Total complete fabrication of the truth. Does the air that flow up from the cab cause a vacuum that the front of the 5th wheel just slips though with no drag too? A 5th wheel simply has more flat-plane drag than a travel trailer. I can assure you from my experience that our New Horizons 5th wheel pulls a LOT harder than the Airstream did. over 30,000 miles with the Airstream we got about 13.3 MPG and with the NH My guess is we'll average about 9.5 MPG. Yes, the NH weighs more, but most of the extra fuel burn is from increased drag. Shame on that crooked salesman.

I asked him how fast he was towing and he said with traffic, which in Pa on I-80 means 75.

Drag increases as the square of the increase in airspeed, so if you calculate the difference in speed between 60 and 75, 75 is 25% faster or 125% of 60. 125% = 1.25, so we'll square the increase in speed - 1.25²=1.50 or 50% more drag going from 60 to 75 MPH. If he is serious about getting better fuel economy, then slowing down is his answer. Besides, 75 MPH is just too fast to tow, it's not safe.

Then there is the factor of headwinds vs. tailwinds. If your BIL is towing at 75 MPH with a 10 MPH headwind, then he is effectively towing at 85 MPH, which is a 28% increase in drag just from the headwind. If he is driving 75 MPH and has a 10 MPH tailwind, then he is effectively towing at 65, which is a 33% decrease in drag.

Hopefully he considers why he got such poor mileage before he makes a rash decision.
 
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Azjeff

Active member
Thread starter
The thing is I don't know what he got on the 2 trips he took or what he thinks is reasonable. I'm not going to bring it up again until we have a couple of trips with ours and see how it does.

Any idea what a 50% increase in drag translates to in mpg loss?

Wayne, what speed do you tow down the highway? I've been comfortable at 65, anything less and you're a real rolling roadblock out here.

Oh yeah, I told him about the front end maybe not having much grease in the joints and he said he'd tell the service writer to have it checked when he got his oil changed. Don't know if he had the FF changed before he started towing, he doesn't put many miles on it.
 
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Wayne

Administrator
Staff member
Any idea what a 50% increase in drag translates to in mpg loss?
That's a good question, I'll see if I can find an answer.

Wayne, what speed do you tow down the highway? I've been comfortable at 65, anything less and you're a real rolling roadblock out here.
I would pull at 60, but always pull at 65 because I don't want to be that guy.
 
Sorry he isn’t happy with the truck. But what the salesman said just doesn’t sound right like all of us think too. I don’t know but sometimes salesman aren’t always the best to listen too for stuff like that. Also thanks for teaching me a new word that I had to look up. 🙂.
 

Azjeff

Active member
Thread starter
I'd pull at 60, but always pull at 65 because I don't want to be that guy.
Exactly.

What the salesman said was garbage no doubt. Mix with a bit of not being well informed plus a bit of hopefulness probably and you're going to be disappointed. It is what it is, the only way to do better is drive slower than he has been and load lighter if possible. That trailer is right at the top end weight wise what most consider a gas truck should tow from what I've seen, not that a 2500HD doesn't have the capacity but it's going to work hard and the gas mileage will be bad.

To be fair he's always been a car guy and still has the Challenger (restored) that he had in high school. He recently had a hip replaced and knees are next I guess thanks to 40 years working outside for the water company.
 

gobi

Member
What RPM is he driving at and which gear?
Then what speed?
What gas did he put in?

Dmax - without any trailer at 75 mph, I will get around 17 mpg if I lunch and there is a gale force tail wind :)
if I keep it below 70 mph and say drive around 68 mph, I can get 20 mpg (thats all before DPF clean hits and everything goes to abyss)

I say, have him baseline his truck without any load, and base line on a known route at different speed.
 

Azjeff

Active member
Thread starter
All I can say is he's offering no information and I'm not asking or giving any advice. I don't know if his mpg is off the dash or calculated. If it's off the dash then it's worse that he thinks.

As they say... not my circus, not my monkey.
 

spasm3

Active member
I tow at about 65, maybe 70 on occasion. Not faster, as i don't think my ST tires are rated for anything more than 70.
 
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