Towing MPG
 

Looking for input re; towing your Cobra in a covered trailer.
My tow vehicle is a '99 F 250 Super Duty crew cab, 2wheel drive automatic w o/d, with 7.3 turbo diesel.
Hiway mpg (no load) 20-22 @ 70mph.
I have towed many types and sizes of trailers, and the worse mpg was 14mpg,
that is until I got a 2006 20' 2 axle enclosed car hauler some years ago with a bent axle. Had both axles replaced @ factory 3-4 yrs ago (torsion type)
My hiway mpg @ 70 has been 10-12 mpg, and the trailer seems to tow "hard", as based on my gas pedal needing to go further to the floor than it used to, to the point that the angle of my foot is uncomfortable for any great distance.
I've had the wheel alignment checked, and while off a bit ,the trailer shop that checked it said it was better than most he sees, and shouldn't be a problem.
Anyone have any thoughts on the subject ??

Ted

I used a friends F350 V10 and enclosed trailer to haul my Cobra from Louisiana to Ohio. Pulled the trail empty to Louisiana. It got ~ 10 MPG both ways. I would expect a diesel to get about 20-25% better.

Unless you have brake drag or low tire pressure, I doubt there is a problem. I think it is wind drag. Enclosed trailers drag a bunch of air. Slow down 10 mph and see how much the MPG improves. Dragging air uses a lot of power and the faster you go the more power it takes.

I have seen some air foils to help split the air in front and close the air back up on the back. I see them all the time on Semi trailers. I expect they save money on fuel.

Old Dog:
I would be happy with 12mpg (no,not really), and being in general aviation for 45 yrs, I understand the aerodynamics of the box type trailer. I am planning to do some re-shaping on the front of the trailer a-la Pete Brocks "Aerovault" car hauler. Love to have one, but don't have 30K to spend on something that doesn't get used very often.
My problem is that I used to get 12-14 with the trailer, and much more @ slower speeds. Something has changed,and I think it's an alignment situation regardless of the trailer shops opinion (" it's not so critical on a trailer") Maybe on the little two wheeler from u-haul, but on a multiple axle 5klb + loaded one, i think it is.
The only other factor I can think of is the truck itself. Still get 20-22 mpg @ 70mph without trailer, but maybe engine is a little down on power, but not enough to make a difference without the trailer, but is struggling with the additional load.
At only 164k mi, the engine should be ok, but will run this question by my local diesel guy.
Thanks for your input.

If a brake was dragging or a tire misaligned to the point of decreasing fuel economy they would reveal themselves in a dramatic way, (smoke followed by flames).

I would not rule out brake drag. Yes when they drag hard they get very hot, but they can drag lightly and not get hot enough to notice.

My 98 Ranger slowly dropped to 18 MPG. It had been at 18 MPG for several years. Over 200K miles, I just figured the O2 Sensor was off, since it was never replaced. One day someone stopped hard in front of me, I realized the back brakes were no longer working. The cylinder were frozen and the lining had come off the shoe and was dragging. Everything was rusty from the heat but I had never notice any signs other than the MPG. After fixing the brakes, the MPG was back up to 21.

My son's 2010 F350 diesel was down a bit on fuel mileage. He had a front caliper stick while towing his camper a couple turns from home. He got out his IR Gun and all four wheel's were way hotter than he expected. Turned out they were all dragging. Replaced the calipers and fuel mileage jump back up.

My 98 Range felt like it gained a bunch of power, after I fixed the brakes. I also noticed it coasted a lot longer and farther when you let off the gas.

My son commented he hadn't really noticed a power loss on his diesel, but after the brakes were fixed he noticed it had a lot more power.

You do not notice a slow change, but after they are fixed you do.

Shoot your rotors with an IR temp gun after a 30 mile drive, and see what you get.

also shoot the trailer.

Brakes on both units are good, ck'd both by me and the trailer shop( Electric on trailer}
I was present at the factory when the axles were replaced, although not close enough to verify their accuracy. They did have a crude looking jig for the job. I remember anticipating drastically improved mpg on the trip home (1200 mi) Nope!! No change at all ! still 12 mpg ! Also I was having about i blow-out per trip and asymmetrical tire wear and constantly replacing the tires that didn't blow out !
There are generally two ways to check trailer wheel alignment.
1. measure from front of coupler with string to axle tip. Distance should be the same, both sides.
2. Hold straight edge horizontaly across tire sidewall. measure distance from straight edge to frame, front and rear of each tire. Compare front and back #'s to determine toe.
I checked mine using method #2, and found both right side tires showed 1/16" toe in.
Seems about right.
However, the left showed 3/16" toe in ! Obviously both axles had been installed (welded) crooked !! I should be able to have someone cut a reweld them, moving the left side back untill there is 1/8" toe-in on both sides. If these toe dimensions were on a car, the tire scrub would make it hard to move. I fail to see why it would be any different for a trailer !

Driving with dragging brakes 'till the linings fall off and brakes don't work. Hope I'm never in front of you...

Keezling:
Where did I say the brakes were dragging ? I said they were checked (both truck and trailer) and all are good ! Just brought it home this am, brakes were never better!

Sorry. Speaking of old dogs post...

2015 F350 Diesel with 20' all aluminum trailer with torsion axels. I get 9.5 mpg with or without car in trailer.

Attachment 29044

I just did a round trip from Phoenix to St. Louis and back, hauling a Cobra each way.

My average for the trip was 11.5 mpg, and I was getting 13mpg while running 80mph across I-40.

Truck: 2006 F350 with Bulletproofed 6.0 diesel (165k miles)
Trailer: Haulmark Edge "Low Hauler" 4500 lb rating