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Poor towing mileage?

Max Attitude

Max Attitude

Typical White Person
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Location
Alto, MI
My dad has an 06 LBZ and when he tows his mileage drops a lot. He gets about 15-17 mpg average not pulling anything. When he hooked up a 3,000# flatbed trailer with a lawnmower he got 10 mpg. He has hand calculated the mileage and his DIC is pretty close. I talked him into a predator programmer before he left for a trip out to Colorado. He is pulling the same trailer with 2 quads on it and getting between 10-14 mpg. 10 was on the hills. He had gained 3-4 towing down the highway here in MI. Is this mileage normal? Seems like you here a lot of Cummins guys talk about 16-18mpg towing. My dad probably goes about 70-78 mph on the highway (where speed limit is 70). I know higher speed doesn't help mileage but still seems a little low.
 
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Sounds about normal (10-14) depending on driving style, tires, wind load, etc. Once you get to 70 mph and above the mpg drops off pretty quickly. Which tune is he running with the Predator?
 
Mine is 8-10 towing and 16-17 empty on the 06, the 08 is 7-9 and 15-17... Sounds normal to me, speed is a factor :)
 
I think the quality of diesel fuel has gone into the toilet. Is he running an additive ? I have been double dosing my fuel at every fill up with power service to keep my milage up.
 
I lose about 1/2 mpg if I forget to put PS in and I also find that B20 loses around 1/2 mpg over straight #2 but I do like the lubricity factor with BIO. My summer mileage is always 16-18 stock unloaded and 12 or so towing. Since I put in the Predator though, I'm running 18-19 unloaded on the 85 tune. Keep in mind I drive 85%+ highway and 130 miles per day.
 
Max Attitude said:
My dad has an 06 LBZ and when he tows his mileage drops a lot. He gets about 15-17 mpg average not pulling anything. When he hooked up a 3,000# flatbed trailer with a lawnmower he got 10 mpg. He has hand calculated the mileage and his DIC is pretty close. I talked him into a predator programmer before he left for a trip out to Colorado. He is pulling the same trailer with 2 quads on it and getting between 10-14 mpg. 10 was on the hills. He had gained 3-4 towing down the highway here in MI. Is this mileage normal? Seems like you here a lot of Cummins guys talk about 16-18mpg towing. My dad probably goes about 70-78 mph on the highway (where speed limit is 70). I know higher speed doesn't help mileage but still seems a little low.
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Does that trailer weigh 3k #'s or is it rated for 3k? Either way, I think that's a pretty good drop in mileage and is not normal....well, it could be, depending on driving style. I towed a dual tandem, 16k pound 5th wheel travel trailer from Texas to Florida with a 07 3500 LBZ dually and got 10.5 mpg...and this trailer was massive. I ran 60mph @ 1600 rpm.
 
I tow a 26' fifth wheel that weighs about 8500lbs. loaded to New Hampshire every year. I get 11mpg going up and 12mpg coming home. Empty I get 18mpg summer and around 16.5mpg in the winter. Sounds like something is up for his mileage to be that low while towing such a light load.
 
Start simple.
Are the tires at max inflation?
Check for intake restrictions. IE dirty air filter and the famous mouthpiece before the turbo restriction that may or may not apply to early production and prior years. The air filter restriction gauge is a decoration as the air filter will implode before the gauge moves - ask me how I know.
Get on the freeway on ramp and floor it till you reach the speed limit - burn the trash out of the kitty.

Are the trailer axles aligned or are they scrubbing the tires off? Brakes working and not shorted to the taillights wire?

Last get used to low teens towing. The aerodynamic drag of a trailer is reason number #1 for low MPG towing. Weight and hills are #2.
 
Sorry guys I completely forgot about this post...thanks for the responses. The trailer weighs about 3,000 pounds by itself. I aired up all the tires and greased the wheel bearings before he left. Clean air filter, fresh fuel filter/oil. I know speed is a major factor. I think he was going around 70-75 mph... I'd have to ask him again. He is running the Tow tune on the Predator.
 
Yup, you're right, tickling 80 mph (70-78 as per OP) is going to suck back the mileage.

For example;

My 2004 300m is pretty slippery. If I set it at 100 KPH (about 62 mph) I can get around 32 mpg highway. If I bump it up to 110 (68-69 mph) my mileage drops to 28-29 mpg. That's 6-7 mph at a cost of 3-4 mpg.

A truck pulling a wide/tall trailer is going to have even more frontal area and drag. MPG penalties woud be even worse for increased speed.

Drag is not linear, it's expotential. Meaning, faster requires a disproportionate amount of power to maintain the speed.

First suggestion for your pops is to bring the speed back a little bit while towing, if MPG is really important to him.

If not, give 'er!
 
Max Attitude said:
Sorry guys I completely forgot about this post...thanks for the responses. The trailer weighs about 3,000 pounds by itself. I aired up all the tires and greased the wheel bearings before he left. Clean air filter, fresh fuel filter/oil. I know speed is a major factor. I think he was going around 70-75 mph... I'd have to ask him again. He is running the Tow tune on the Predator.
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Mileage drops like a rock towing over 60...my LBZ tows our RV at about 12-12.5 at 62 unless it's windy.
You may want to refresh your Dad's driving habits - many of these trailers have ST tires...max speed of 65. Anyone exceeding that is running a VERY high risk of blowing those tires out. Been there, done that. Slow down and be safe. I don't think you want that phone call that his truck is in the ditch (if he's lucky).
 
Max Attitude said:
Sorry guys I completely forgot about this post...thanks for the responses. The trailer weighs about 3,000 pounds by itself. I aired up all the tires and greased the wheel bearings before he left. Clean air filter, fresh fuel filter/oil. I know speed is a major factor. I think he was going around 70-75 mph... I'd have to ask him again. He is running the Tow tune on the Predator.
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Not that it matters but what size is that trailer? My 7x20 dovetail equipment trailer (bumper pull) weighs just a tad under 2k. I'm just getting this humorous picture in my mind of your dad hauling a 19" cut Murray push mower on a 7x30 gooseneck......being pulled by a HD Dmax. lol

:)

I just made my first highway trip (no towing)- kept her right at 70 mph and got 21.5 mpg. Had been getting 18.8-19.7 mpg running back and forth to work. All this on a Borrowed (Thanks to Nick - aka unit453) Diablo Predator on the 80 hp tune.
 
10 MPG on just the hills is really not bad lugging 3K LBS up them.
The Duramax itself, w/o trailer, will go from 22 MPG at 65 MPG to 18 MPG at 80.
 
Odlaw said:
Not that it matters but what size is that trailer? My 7x20 dovetail equipment trailer (bumper pull) weighs just a tad under 2k. I'm just getting this humorous picture in my mind of your dad hauling a 19" cut Murray push mower on a 7x30 gooseneck......being pulled by a HD Dmax. lol

:)

I just made my first highway trip (no towing)- kept her right at 70 mph and got 21.5 mpg. Had been getting 18.8-19.7 mpg running back and forth to work. All this on a Borrowed (Thanks to Nick - aka unit453) Diablo Predator on the 80 hp tune.
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It's a Kiefer Industrial bumper pull trailer 7'x16' and he had a Exmark Lazer comercial mower on it.
 
I get 11-12 towing my 16 ft enclosed trailer empty or loaded at 70-75 mph. It has a lot of drag and I'm building a v nose to cut down on that. I hope to get 12-14 after that empty. I ran into a strong wind coming back from Illinois the other way at 65 and was getting barely 10.
 
cgreen said:
I get 11-12 towing my 16 ft enclosed trailer empty or loaded at 70-75 mph. It has a lot of drag and I'm building a v nose to cut down on that. I hope to get 12-14 after that empty. I ran into a strong wind coming back from Illinois the other way at 65 and was getting barely 10.
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Are you towing with the Predator 85 tune? I'd think your EGTs would be at a pretty risky level when you hit some uphill stretches of road.
 
I tow a 30' 5th toyhauler that weights between 12-13k when loaded. I get between 10-12 mpg down here in Texas flat land. I tow with the Predator on tow and going over steep bridges I can easily get the egt's in the 12's. I have a LOT of wind resistance but tuck up behind a semi and everything gets easier :D
 
You need to get that RPM down under 2k for the peak milage. So far with all the driving i have done with the Predator i believe the 65hp tune has been the best for me for my fuel milage. I have been getting 12-13mpg towing my enclosed trailer and i just came back from the Finger Lakes region and averaged 21.7 mpg including city/back road driving and romping on the throttle. My best so far was 23mpg goign to Maine with the 120hp tune but that was little city driving and no horsing around. All milage is hand calculated and the fuel tank filled to the cap.
 
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