Towing gas mileage

I towed my boat the first time last week using the tow haul shutoff. I got just above 13 mpg towing my 18' flats boat, approximately 3K lbs.

I towed again the same route yesterday not using the shutoff and got just above 14. I noticed a little more shifting but no strain on anything.
I have the 2021 5.7 ET with a 3.92, 25K miles on the truck.

Cabinetman said:

I towed my boat the first time last week using the tow haul shutoff. I got just above 13 mpg towing my 18' flats boat, approximately 3K lbs.

I towed again the same route yesterday not using the shutoff and got just above 14. I noticed a little more shifting but no strain on anything.
I have the 2021 5.7 ET with a 3.92, 25K miles on the truck.

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That's about right. I seldom use tow haul unless in really mountainous terrain. Even when towing heavy, I see no advantage .

Yes, I think that is correct. We pull a TT about 9K and have noticed that mileage is a bit better without Tow Haul.

I have a 2019 with same set up....5.7...3.92.....crew cab....tow package....26,000 mile.....we tow a Casita TT....about 3500 lbs......on most recent 1500 mile trip.....I averaged between 16 and 17 mpg.....this was towing up the Oregon coast.....lots of hills......when not towing.....I average 20-21 mpg. I rarely use tow mode.

I greatly prefer to use tow haul when pulling basically anything. It'll burn more fuel in some situations, but higher RPMs is drastically easier on the whole drivetrain. If I had an aisin transmission and deep ratio rear end I would use it less.

My owners manual says to only use tow/haul mod if the truck is shifting frequently. I don't use it much.

Interesting, I always use tow/haul when towing with my cummins. I fine that its a lot smarter about engine braking.

Cabinetman said:

I towed my boat the first time last week using the tow haul shutoff. I got just above 13 mpg towing my 18' flats boat, approximately 3K lbs.

I towed again the same route yesterday not using the shutoff and got just above 14. I noticed a little more shifting but no strain on anything.
I have the 2021 5.7 ET with a 3.92, 25K miles on the truck.

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What were your trans temps when not using tow haul vs using tow haul?

I'm not saying this is you but I've seen it plenty of times where a guy saves a little bit of money only to have to spend a lot on a new or rebuilt transmission.

Are we sure that T/H doesn't do other things to the transmission, like increased line pressure or something of that nature?

There is a lot of steep country in the West and some long grades. I use tow/haul even when not towing sometimes.

Fake-Account27 said:

Interesting, I always use tow/haul when towing with my cummins. I fine that its a lot smarter about engine braking.

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Engine braking still works great when not in tow/haul mode. Mind you, I don't haul heavy. If I were hauling a big RV/5th wheel, I'd probably use it more, at least in rolling terrain.

ramffml said:

Are we sure that T/H doesn't do other things to the transmission, like increased line pressure or something of that nature?

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It modifies the behavior of the drive train. I dont think it affects line pressure, but it does change torque converter lock/unlock points, shift points, engine or exhaust braking behavior, and clutch apply speed.

The fuel burn difference between having it on or off is going to be dictated more by your right foot than anything else. All else equal, 4th gear vs 5th gear isn't going to drastically affect fuel burn. It is going to drastically change the amount of torque in the driveline, and less torque for the same amount of work equals less stress and wear on everything. Even with the diesels, it's good to let them spin up if working them. Alot of 68RFE failures are results of working hard in 6th gear with torque management turned off. The engine doesn't particularly care a whole lot because it's big enough and it'll make torque to spare, but it'll chew up everything behind it.

Higher engine RPM also means higher coolant, air, and oil flow rates for drastically better cooling, higher fan speed, higher transmission fluid flow rate. Even when towing light, burn the little bit of extra gas, slow down a little bit more, and enjoy the ride.

Interesting that so many don't use tow haul mode when pulling a load. I use it with my Travel trailer and car hauler not because the truck won't pull them in normal driving mode but in tow haul the transmission is programed to down shift quicker when slowing down and will downshift on slight inclines to help hold your speed,this helps control your load and saves on brakes. Can't believe y'all haven't noticed or checked this out with your trucks. I don't actually care about a little better fuel mileage while not using the tow hall it's more about better control and driving experience when pulling a load.

I love T/H with the Cummins. Towing about 4,500 pounds up and down moderate western grades at 75 mph, I get about 10 or 11 mpg. That is pretty much the speed limit. Mpg would be better if I slowed it down. I don't know if iT/H decreases fuel efficiency, but it sure helps with engine braking. And exhaust braking, which I use mostly on longer grades, is also much improved. Tranni temps are mostly around 168 degrees.

My camper is 7000lbs empty. Probably closer to 8500 loaded up. I exclusively use tow/haul mode. Not worried about a 1 mpg difference if it means the drivetrain operates better. For most level highway/expressway driving I will put on cruise control too. It shifts less.

I also have a 20ft boat that's around 3000lbs too. I use tow/haul for that as well. It just seems to tow it much better.

Jerrybob said:

I have a 2019 with same set up....5.7...3.92.....crew cab....tow package....26,000 mile.....we tow a Casita TT....about 3500 lbs......on most recent 1500 mile trip.....I averaged between 16 and 17 mpg.....this was towing up the Oregon coast.....lots of hills......when not towing.....I average 20-21 mpg. I rarely use tow mode.

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A Casita is very aero friendly; especially when towed by a 1500.

Get a traditionally shaped TT and you will benefit from TM.

DA Smith said:

Interesting that so many don't use tow haul mode when pulling a load. I use it with my Travel trailer and car hauler not because the truck won't pull them in normal driving mode but in tow haul the transmission is programed to down shift quicker when slowing down and will downshift on slight inclines to help hold your speed,this helps control your load and saves on brakes. Can't believe y'all haven't noticed or checked this out with your trucks. I don't actually care about a little better fuel mileage while not using the tow hall it's more about better control and driving experience when pulling a load.

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Exactly my thoughts.

From my owner's manual:

"When To Use TOW/HAUL Mode
When driving in hilly areas, towing a trailer, carrying a heavy load, etc., and frequent transmission shifting occurs, push the TOW/HAUL switch to activate TOW/HAUL mode. This will improve performance and reduce the potential for transmission overheating or failure due to excessive shifting. When operating in TOW/HAUL mode, transmission upshifts are delayed, and the transmission will automatically downshift (for engine braking) when the throttle is closed and/or during steady braking maneuvers. "

So, when pulling my 2600 pound snowmobile trailer, I don't have the "frequent transmission shifting" so it isn't needed. When I'm pulling my 7600 pound travel trailer I do use it. As others have said, there are many more reasons for the tow/haul mode than gas mileage.

Pulling the travel trailer last summer I also noticed some things while experimenting with on vs off. I think that the ideal that you get worse gas mileage with it on is a false perception. I'm talking about with the travel trailer, not the light weight snowmobile trailer. So with to/haul on, the engine seems more reluctant to shift into higher gears and is often running at a bit higher RPM than it would with tow/haul off. Many people seem to operate under the assumption that higher RPM = more gas used. But my experience is that this isn't always the case. I've often seen the instantaneous fuel economy number not change when the truck down shifts and runs at a higher RPM. It seems to me the T/H mode is keeping the engine at an RPM where its more efficient. In my experience, I've seen no perceivable difference in economy between on and off when hauling the heavier trailer.

I'm now in the hills of extreme NE TN and any drive is like a roller coaster. I use T/H mode because it makes my truck behave more like I would do if I had a manual trans. These hills are full of momentum killing switchbacks and the truck doesn't know how close the next one is so it's never engine braking or holding a gear longer if I don't use T/H.

I use T/H with any trailer unless it's a small trailer that is empty, so under maybe 1500lbs