So I just got back from a short camping trip and was coming down a 5-6% grade without the exhaust brake on and my truck and trailer stayed pretty steady at 60 mph ('18 6.7 CCSB 3.55 gearing with 31 ft empty toy hauler probably weighing in at about 7-8K lbs). I was pretty surprised by this thinking that I'd need to use engine or exhaust brake for sure but assumed it was just the mechanical and air resistance of the truck and trailer keeping me there (there wasn't really a headwind as far as I could tell).

Then I got to thinking that my fuel mileage... Even while on flat ground doesn't seem to be on par with some of what others say they're getting while pulling much heavier loads. According to the lie-o-meter I averaged 10.something for the trip but I haven't hand calculated yet (every time I do the computer is usually about .5 - .75 mpg higher than actual. I also spent a little time driving while unhitched and conservatively during this period.

I also got to thinking about how my trailer brake gain is set to 8.5 which I think is high.

I wanted to see if this sounds normal to you guys. Does a higher gain setting make the brakes drag and could that be causing my poor gas mileage? I haven't noticed any burning brake smell after any pulls. Could my wheel bearings be shot causing added friction? Or maybe this is just normal?

The truck seems to pull the trailer fine with plenty of power but I'd guess these things have enough power to pull through almost anything that could be a problem.

 

Trailer brake setting definitely seems high to me, but it has zero effect on you just traveling down the road. It just applies a higher voltage to the trailer brakes so they brake harder when you tap the brakes in the truck.

I think you're getting fine mileage for that trailer and weight. And if you were in Tow/Haul mode it will rev a little higher on down slopes, so that might be the resistance you are noticing.

 

Go pull the trailer around for a while and find a place where you can basically coast to a stop or turn down the trailer gain so they are not used in any way for that last braking action (of course do this safely). Jump out and check the temps of your brake drums and bearings. They should be cool or at most slightly warm to the touch. If they can fry bacon, you have a brake dragging or a possibly a bad bearing. Temps can tell you a lot about what is going on or if a drum is not doing it's fair share of the work if it is cooler than the other 3 or 5 drums after a good braking action.

 

Thanks for the clarification on how trailer brakes work - I was **thinking** that was the case but had trouble confirming. I was in Tow/Haul mode so maybe that's what it was... I'll switch between the two modes next time to see how that impacts things.
Thanks for the suggestion - I'll give that a try next time I have my tow rig and trailer together!

One other thing - I was also dropping to 4th gear pretty often on the way up which I'm guessing is normal for the grade and weight but I also feel like I've read things here like "I did a 10% grade in 6th gear and the turbo spooled without downshifting no problem" (slight exaggeration =P). Would you all agree that dropping as low as 4th is to be expected/normal in a grade/weight situation like I was in? I should probably stop reading forums... lol.

 

An even better way to check your brake and axle temps is to invest in an inexpensive infrared thermometer. They can be had for the cost of a case of beer. Carry it with you on your trips...you'll be amazed at how handy they are, from checking axles, brakes, a/c output, the evaporative coil on the rv fridge, etc., etc.

And, you'd be wise to take most of the mileage claims you see with a grain of salt. Anybody can make a claim be what ever they chose. My "lie-o-meter" continually read higher than hand calculated. I tweaked the engineering value a bit and went too far. Now it reads lower than hand calc'd, so I need to tweak it the direction a bit. I have dirt bike riding buddy who embellishes just about any story he tells. His new 5.7 Hemi Ram is in the high 20's on a trip... Yeah right. Before the next time we take a trip I'm going to tweak my "lie-o-meter" to show 30 mpg. Then that report will be floating around out on the interwebs too.

 

I just got back from my first long tow (1700 miles round trip from San Diego to Southern Oregon) with my almost new truck (6 months and less than 7,000 miles) and new fifth wheel. I also have 3.55 gears and the trailer was probably at 11K + pounds. There are plenty of steep and long grades along the way. Per the lie-o-meter, with the adaptive cruise mostly set a 65, I got 10 MPG. For the first fill-up I was at about 350 miles and the truck said 10.3...hand calculated came out to 10.5. The truck was under reporting my fuel economy! Anyways, the trucks calculation is more than close enough for me. I think your fuel economy is reasonable.

I played around plenty with the engine brake. I actually could not notice any significant difference between Tow/Haul alone, T/H + engine brake, and no T/H + engine break. It seems to me that T/H and the automatic engine breaking are redundant. I eventually left it in T/H and let the transmission downshift and engine rev. It did a fabulous job of maintaining my speed.

4th gear was typical on most steep grades. With a some momentum, others were taken in 5th. A couple of times, it shifted into third when trying to recover speed after getting stuck behind a semi trying to pass another semi. Many lesser grades never prompted a shift out of 6th.

To set the gain, find a level road and get you truck and trailer up to 25 MPH. Manually apply the trailer brake. If the trailer tires lock up, reduce the gain. The goal is to have it set high enough to smoothly slow down the trailer without locking up the tires. Mine is currently set at 7.5.

 

Drag is the mpg killer. At highway speeds I get pretty much the same mileage pulling my 40' gooseneck weighing in at 10k as I do my aluminum enclosed trailer that weight 3500#.

 

Think there are 3 settings (low,med,high)for the trailer brake besides the gain, you set them when you do your trailer setup.

 

Good call - I think an amazon order is in my future...

I appreciate hearing about your experience - I just unhitched and parked the truck, I'll hand calculate mine when I fill up next. I went through and did the adjustment on the lie-o-meter and got it to within the .5-.75 and figured it was close enough for me. Before doing that I was almost a full 2mpg off!

Glad to hear this because I was just thinking "wait a minute, JD's got the same MPG for a much heavier trailer"

I actually just discovered this during my trip and tried all three settings, it still felt most right set with the gain at about 8.5 or 9. Of course I don't have any past experience to base what feels "right" on. I'm going to hook up and take work my way up from a lower gain setting to see how she reacts soon.

 

For OP's reference: 1700 miles round trip pulling a 31' TT ( @ 9500lbs ) with my 17 F250 3.55, 6.7. I had engine brake on the whole time ( not on auto engine brake). I averaged 10.8 mpg from upstate NY to Coastal NC.

 

When you set your trailer brakes, if you can imagine...you want to just feel the trailer brake in the seat of your pants when you hit the brakes. Too much gain and the trailer is trying to stop the whole rig. Too little gain and the trailer will be trying to push your truck...AND your truck will be doing too much work.

As far as MPG goes. I drove a big rig for many years. You REALLY need to learn how to use the engine without over working it. These new trucks simply have a TON of torque available. I pull a 31ft fiver with a 12ft trailer doubled up behind it...carrying my Side by Side. I can pull the hill into Flagstaff at 90 MPH or the grade outside Bishop doing almost the same. However, I will be sucking up the fuel and also burning the rubber off my tires. I have not yet pulled my rig with my 2019 but, with my 2012, I could average 11.5ish MPG if I simply let the truck run in it's sweet spot. So far, it looks as though my 2019 is going to do a little better than that. Hopefully I can draw some good deer and elk tags this year so i can try it out!

 

Have you checked the pressure in your tires on the truck and the trailer? low tire pressure will hurt MPGs. also, some people have seen significant mileage increase with higher quality trailer tires. the factory installed trailer tires are usually junk

 

Two of my friends have Ford diesels and pull 5er's; they are both getting low 10's for towing mileage. 12K 5er's at 65 to 70 mph.

 

FWIW, I just finished my trip from WA to VA (3k miles in total) with my 19 F250 PL 6.7 with 3.55 gears. I was fully packed with my family of 4 while pulling our 29' RV. Weight slip was just shy of 19k in total.

I got 11.9 MPG with Eng Brake on whole time and mostly auto cruise between 62-68 MPH.

My truck does have a full emissions delete, Motor Ops tune (used its lowest setting the entire time, +25 rwhp) and an S&B cold air intake.

 

Planning on pulling my trailer up to the Payson area for a last minute camping trip. Last time I tried adjusting the brake controller I could not get the trailer to lock up the brakes. Anyone ever have that issue?
this will be first time pulling my 26’ TT (6000lbs) up to the rim which I’m looking forward to with my truck.
The engine braking is new to me. Can anyone fill me in on using it?