I was just wondering what kind of mileage you guys are getting when towing.
Today I completed a round trip from northern Utah to Montana and back. I have a 28' TT that weighs around 8500Lbs loaded. We drove a lot of back roads up to Montana and I averaged 8.5MPG running 58MPH at 2300 RPM. On the way home we drove I90/I15 all the way. There was a lot of headwind so I couldn't run in OD, so i ran OD off at 2300 RPM and averaged 7.9MPG all the way home. Is this mileage normal? I was hoping to upgrade to a 5th Wheel in the next few years, but at this poor milage I don't know if i could handle the extra weight.

 

Why were you running with OD off??? Was your speed slowing down? I do see you have 3.73 gears. Running that high of RPM is no doubt a fuel eater. A headwind will get you on MPG but not that much. I normally will get 10 MPG if I am in a bad headwind. If not I get 12 to 13 MPG.

 

I was running with the OD off because it was shifting in and out trying to hold 70 mph on the flats.

 

I have heard of that happening with 3.73 gears. The only thing you could of done is speed up to 73-74 MPH. The best thing would be to switch to 4.10 gears but that would be costly. A Smarty Jr. would help you out though. Should give you enough to keep it in OD.

 

I would love to get a Smarty Jr, but don't want to tear up the transmission.

 

I ran a Quad Std for a year and a half with no issues. What you have to watch out for is slipping the lockup clutch around 60 MPH while in OD. At least that is what speed it was at for me while towing. I drove it like that for 6 more months before I sucked it up and did the tranny. If I noticed the RPM's rise I eased out of the throttle. You just have to use the throttle carefully while towing and in lockup.

Oh, keep it on the lower settings while towing and no hot rodding from a stand still.

 

Tow the same bumper pull and get 12-14 mpg. Don't spend too much time in 3rd. Only use overdrive off to get up to speed and press the button. I do drive by my gauges though, try to maitain boost at 8-10 and pyro 600 -900. High rpm on the flats kill mileage. The cummins is the torque king learn to use that low rpm torque.

 

I am beginning to wonder if i might have some other issues, like injectors. My truck just doesn't feel very strong when pulling in OD, like I have to keep my foot to the floor. Best mileage ever when towing was 10.5 MPG and that was on the flats with a tailwind. 70 MPH in OD

 

As long as you keep it in the lower settings it should help your Mileage and towing torque,,, from what I understand,,,, the Jr, is made for stock driveline setups as long as you keep the tranny serviced you should be alright,,,

 

When is the last time you changed your fuel filter and air filter? Another thing, do you still have the factory lift pump on the back of the filter housing. If you do, you may have a bad one and need the intank conversion or upgrade to an Airdog 100.

 

With your tires you should be at about 1850 rpms at 70 MPH in OD (assuming 285/75). I would think that the truck would hold that with no problem and be more efficient than what it is. I switched my gears to 4.10's because I have 35" tires and the RPM's were too low. It would lug the motor some trying to pull my 5er up some hills when the speed dropped down which made the egt's get high and the fuel mileage suffered. It would also downshift if the rpm's got too low( 65 MPH x 3.73 x 35" tires= 1600 rpm). I find that my truck is most efficient towing at 1800-1900 rpm's (65-70 mph). Much over that and the wind load at that speed deteriorates the fuel economy.

For reference, I just completed a 3000 mile trip pulling my 5er(32' ~12000lbs.). I was leading 3 other rigs similar to mine so I had no one in front to break the wind(no pun intended) for me. Most of the trip was between 65-70 MPH. In an effort to hold the speed steady for the others, I would set the cruise and let the motor eat (not good on MPG's), on all but the steeper hills. I was able to top La Veta pass @ 60 mph in OD with the egt's never exceeding 1300*. Raton pass I kicked it out of OD due to the egt's. Over the course of this 3000 miles, I averaged 10.0 MPG while towing. Not too bad considering I have a lift and 35"x13.5" tires on a late model 3rd gen.

My suggestion is to get yourself a set of guages (egt, boost, transmission). That's right, I said gauges on a bone stock truck that tows. It never hurts to monitor what the motor and tranny are doing. They will often let you know something is not right with the drivetrain before it becomes something major. They will also help you to troubleshoot situations such as you have now. For instance, if you know that your truck usually pulls x psi of boost pressure running on the flats and now it is only running y<(x) psi. It might point you to looking for a boost leak,etc. If the egt's are running a lot higher than normal, is it because your bucking a headwind or is it because of a boost leak,etc. A high tranny temp might point you at looking at it to see why. A lot of these types of problems can also lead to poor mileage towing. And the plus is,You will already have the gauges when you decide to get that Smarty Jr. that you know you want.

Sorry for the long post. I wish you luck

 

Thats good information, and I appreciate the long post.

 

I change the fuel filter when I change the oil, every 5000. The air Filter gets changed when I service the Trans, every 3 oil changes. I do have the in tank fuel pump. I plan on adding the Glacier 2 micron filter in the next few months, I understand that can increase the life of the Injectors.

 

Sounds like you are good on maintenance stuff and LP. It just sounds like a gearing issue. The only thing you can do is add power, change gears, go back to stock tire size, or just live with it.

 

Well I have thought seriously about changing over to 4.11's