Towing 5er with 2500HD

Paddler · 04-25-2011, 04:23 PM

I've towed a travel trailer with my 2500HD for the past 4 years. I generally tow at 55-60MPH in 6th with tow/haul mode off.

Now we have moved up to a 5er and I'm at 91% of the CGVWR. I'm finding that to continue towing in the 55-60 MPH range with tow/haul mode on, the truck is humming along in 5th gear. So the questions to my fellow GM Duramax owners are:

1) Do you just speed up to 65 to get into 6th? If so, how bad is the fuel economy? (assuming no wind issues.)

2) Turn tow/haul off to get into 6th at 55-60MPH? With tow/haul turned off, do you see an increase in transmission temperature?

or 3) Just sit in the right lane at 58 MPH and enjoy the view in 5th? I have to admit not having to pass other vehicles makes this choice attractive to me.

Festus2 · 04-25-2011, 05:16 PM

I have an '05 GMC Duramax which doesn't have the 6th gear/manual choice that you do. However, I pretty much always tow with the Tow Haul on - letting the computer make the right choice for me as to which gear it should be in. I am also towing a smaller and lighter 5th wheel than you. If I read the Owner's Manual correctly for this year -2005 , that is what is being advised - leave it in Tow Haul. Isn't that what it is designed to do?

Perhaps with the addition of another gear (6th), using the Tow Haul may be slightly different?????

NSTS1470 · 04-25-2011, 07:09 PM

Just towed for the first time with my 08 gmc sierra 2500hd with duramax/allison. I towed about 45miles up without tow haul mode and back 45 miles with it on. I will deffinately will be leaving it on for all trips. Being my first diesel I pushed it and was towing anywhere form 65 to 80. Tow haul worked great and my milage was comparable to it being on or off at around 13.4mpg. Now that I've got it out of my system I will be driving a safe 65mph. I especially liked when going down grade the automatick down shift to help on braking. Alothoug I'm only towing a 33 ft keytone laredo with a dry wieght of 6200. My tow rating is 13,6000 so mabye loaded my have the towing capacity.

Also my tranny temp was the same both trips hovering around 170 to 179.

Paddler · 04-26-2011, 10:41 AM

Thanks for the quick responses. If I remember my manual correctly, tow/haul mode should be used whenever your CGVW is greater than 70% of max. Or when you want more engine braking. (long downhills) When I was towing the travel trailer (7800 lbs) I was well below the 70% threshold so I only used Tow/Haul for hills. Now, I guess I'll just have to get used to running in 5th or speed up!

Paddler · 06-26-2011, 10:15 AM

We just returned from a slightly longer trip, about 60 miles one way. I've found if I leave the transmission in Tow Haul until I reach my normal cruising speed 58 MPH then tap T/H off, the transmission will shift into 6th. Tapping T/H again will turn T/H back on and she will stay in 6th.

I've had some concerns about the 2500 pulling such a heavy trailer, but after today I'm no longer concerned. Just a matter of learning the new combination.

animalcracker · 07-24-2011, 01:33 PM

something i learned today is that whether in tow mode or not i got better fuel milage at 60 mph in 5th gear then at 60 in 6th. even though in 6th gear rpms was about 3 or 400 less. and fuel milage went down hill from there no matter what! i have the 06 gmc.

puresilver66 · 07-25-2011, 10:01 AM

You've got a great truck. Use the tow/haul button and don't try to outsmart truck.

cumminsdad08 · 07-25-2011, 04:04 PM

easy solution, dump the allison and get a manual

, J/K. i had an 08 chevy gasser, and my dodge is a 6 spd, manual, and i thought that 1st gear was just a little lower then on the 5 spds. at least that is the way it felt in my gasser. when just driving with no load at all, it would pull out in 1st and instanly jamb 2nd, and cruise on from there. if it persists to bother you, you can buy tuners that will adjust your trans, shift points on an automatic. i actually took my gasser in to the dealer just after i was put in it, and had the first 3 gears changed around( it was a work truck, with a heavy topper on it), it was done at not cost to my company, but that could have fell under the warnty.

animalcracker · 07-25-2011, 05:07 PM

Quote:

Originally Posted by puresilver66

You've got a great truck. Use the tow/haul button and don't try to outsmart truck.

i was actually using it in the manual mode in 5th. it worked great because when it would shift to 6th every time i would go up a slight hill or an over pass it would shift down to 5th again. and as i said before it got better fuel mileage just leaving it in 5th even though it was running 3-400 rpms more.

Paddler · 07-25-2011, 06:22 PM

I believe you are correct AnimalCracker, 5th does seem to deliver better fuel economy than 6th (@58MPH). My first couple of short trips netted about 12.2MPG in 5th and the last couple of short trips were about 11.5MPG in 6th.

Just have to play with it some more to find the best combination. I'm kinda liking the manual mode. As to running a tuner...I'm still under the 5yr/100K warranty so no point in voiding that. If I had the spare $25K, I'd trade up to a one ton, but until then I'm very pleased with my 2500.

cumminsdad08 · 07-26-2011, 04:47 PM

food for thought, some of the tuners don't leave a trace on the ECM when taken off.

as for MPG, sometimes i hold out fifth gear to keep her running around 2,000 or so, that seems to keep the load down(which i can keep an eye on that percentage on my tuner screen

), keeps the boost at a nice level for the slight hills you come across( also on the tuner screen

), and also keeps the EGT's at a nice level(i will let you guess how i keep and eye on that one too

)

when the engine is running around 2000, it really sounds you should be changing gears, but infact i have seen many discusions on this you are actually getting good MPG's. this holds true to my dodge, i have not taking the time to see how it holds out in my auto, duramax. maybe someone can chime in on that one

Paddler · 07-27-2011, 03:41 AM

Hi Cumminsdad08,
I have a Scangauge 2 connected to my CAN port so I too am monitoring some of the interesting data the truck records. My new favorite is the ability to measure the engine torque currently being produced. Taking that reading and comparing it to the TPS reading convinced me that running in 5th @ 58 is more economical than running in 6th.

Tuners are nice, but so far I don't have any complaints on the power aspect of my 07 Duramax, she produces more horsepower and torque, stock; than the new 2011 Dodge 6.7L base motor.

cumminsdad08 · 07-27-2011, 11:39 AM

i "mostly" only put mine on to monitor things a little bit, but i wont lie to ya, it sure does have some fun points, in mud and snow.

truthfully, i usually turn the truck down a little bit when i am running on the highways. it lacks the response that it usually has when running stock, but boy does it usually help the MPG's. my only complaint with mine is that i can only watch 4 things on the screen. and one of them is burnt up on my MPH( i have way larger tires then stock, and this has saved my hide a few times), so i was considering putting a few perment gauges on to open up some space to watch the percentages on the digital monitor.

Jim W · 07-28-2011, 07:52 AM

Quote:

Originally Posted by cumminsdad08

food for thought, some of the tuners don't leave a trace on the ECM when taken off.

That is true on the older 5.9L Cummins ECM and maybe on the other diesel engine manufactures, but not today. When the new 6.7L Cummins was introduce in Jan 07, the ECM where changed. The ECM can and does record that a tuner was installed on it. This is true for the 2010 diesel engines that meet the current emission standards, on other pick-up trucks too. In fact Mads Electronics, the maker of the Smarty has this information on their web site.
Jim W.

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