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xo1rider · 10-22-2012, 07:23 PM

I've been towing with the tow haul mode on 100% of the time.

Just curious, when on a flat, straight road at sea level can I or should I turn off the tow haul to reduce RPMs and increase MPG?

dznf0g · 10-22-2012, 07:27 PM

Tow haul mode is only necessary under any and all conditions, when your GCWR is 75% of max rating or greater. Based on your trailer (unless you're hauling lead in the truck bed) you don't need tow haul turned on at all. Is there more info that would validate a 75% load situation?

xo1rider · 10-22-2012, 07:33 PM

Quote:

Originally Posted by dznf0g

Tow haul mode is only necessary under any and all conditions, when your GCWR is 75% of max rating or greater. Based on your trailer (unless you're hauling lead in the truck bed) you don't need tow haul turned on at all. Is there more info that would validate a 75% load situation?

Thanks, I doubt if I'll ever be at 75% with my truck (which is why I tow with this beast).

Am I correct that my gas mileage will increase with the tow haul off? I imagine that it must help based on RPM. Actually I'm in love with the Duramax and even the current MPG is not bad.

dznf0g · 10-22-2012, 07:37 PM

Sure, it will help. You will shift sooner and stay in, respective to speed, higher gears more; and downshift later.

I just got out of my 2500HD Sliverado Duramax demo, unfortunately, and I never used TH mode all summer. I may have punched the button if I would've gone to the rockies last summer, but other than that....not needed. This is explained in your owner manual under "tow haul mode".

aswbe · 10-22-2012, 07:56 PM

I replaced my duromax tranny this summer ($5000) after 55000 miles of mostly towing and mostly not in trailer mode. The manual in my '05 truck is less than clear on what happens if I don't use it only the benefits of using it. But now knowledgeable mechanics and articles I have picked up all point to the shifting into and out of OD at cruising speed (which apparently will happen frequently)as the culprit for the destruction of the gears. If you don't want to use trailer mode then hit the button twice to disconnect OD.

I now only tow in trailer mode and see no decrease in MPG. By the way the official reason the dealer gave me was the torque converter was loose...others were quick to add as the result of the OD cycling.

dznf0g · 10-22-2012, 08:01 PM

Quote:

Originally Posted by aswbe

I replaced my duromax tranny this summer ($5000) after 55000 miles of mostly towing and mostly not in trailer mode. The manual in my '05 truck is less than clear on what happens if I don't use it only the benefits of using it. But now knowledgeable mechanics and articles I have picked up all point to the shifting into and out of OD at cruising speed (which apparently will happen frequently)as the culprit for the destruction of the gears. If you don't want to use trailer mode then hit the button twice to disconnect OD.

I now only tow in trailer mode and see no decrease in MPG. By the way the official reason the dealer gave me was the torque converter was loose...others were quick to add as the result of the OD cycling.

Hmmmm, don't sound right to me. Even with my 30'er, in the midwest, even in and out of the river bottoms, i only very occasionally dropped out of 6th into 5th. Sumptin' else going on here.

aswbe · 10-23-2012, 10:25 AM

I questioned that too (not aware of the shifting). I am not enough of a gear head to argue the point and there may very well be some other assignable cause. But my mechanic had seen this many times before from local farmers who do not use tow mode because they see no reason too and a new transmission is covered by warranty. As for me I will use tow mode until the warranty expires in 3 yrs and buy another.

Bill M. · 10-23-2012, 11:04 AM

On a flat, level road I think the rpm will be the same in tow haul or regular. On our Dodge the up and down shift points are different, but at speed on a flat road T/H gives the same rpm. Try it and look at your tach. If you stop and start a lot you will probably loose a little mpg in T/H, and it is probably worth it for the better shifting and transmission life. Sometimes in the mountains or in the city I run it in T/H even when not towing. We do not have all those gears that you do in the Allison and I like the way it shifts in T/H in bad mountains.

dznf0g · 10-25-2012, 09:52 AM

Yes, once in a particular gear, the mileage will be the same. BUT, with TH on, you will stay in lower gears longer and downshift sooner resulting in higher RPMs for longer amounts of time than if TH was off. So mileage will be a little lower....how much....I don't know, never experimented. I'd guess in the flatlands, less than .5 MPG certainly, and probably less than that.

Pahaska · 10-25-2012, 07:05 PM

I tow at about 62 indicated (true 60 1/2 according to my GPS). In tow-haul, it will not shift into 6th gear at that speed. Accordingly, I always stay out of tow-haul except in very hilly country. On flatter country, I can stay in 6th for long periods, so there is a minimum of shifting in and out of 6th. BTW, even 5th is an overdrive.

In hilly country, running, always, in OD, I shift into "M" and use the button to downshift when I sense that I am nearing a shift down. That shifts early enough that the shift can hardly be felt and I never get into a position of getting a double shift down. As I near the top of a hill, I use the button to shift back to 6 and let the truck decide when to make the shift. I get the best fuel mileage that way and it gives me something to do.

I have had two Durmax/Allisons and never a transmission trouble.

Alumaholic · 10-25-2012, 07:31 PM

...on just about everything, I must disagree on this one.
What I loved about my 5-speed Allison, and what I love even more about my 6-speed Allison, is towing in the mountains in the Tow-Haul Mode.
Otherwise, in the wide open spaces, I don't use Tow-Haul because it tends to hold me in lower gears too long. But when I am in the mountains and descending(using Tow-Haul), I love the way the transmission down-shifts and provides engine braking. All I have to do is steer.

dznf0g · 10-25-2012, 08:30 PM

Quote:

Originally Posted by Alumaholic

...on just about everything, I must disagree on this one.
What I loved about my 5-speed Allison, and what I love even more about my 6-speed Allison, is towing in the mountains in the Tow-Haul Mode.
Otherwise, in the wide open spaces, I don't use Tow-Haul because it tends to hold me in lower gears too long. But when I am in the mountains and descending(using Tow-Haul), I love the way the transmission down-shifts and provides engine braking. All I have to do is steer.

Um, I don't think we disagree...way upthread (post #4) I discussed using it in the mountains. All my other comments were relative to the flatlands around the midwest.

Also, we have 30'ers....op has a 27'er....maybe 1500 lbs difference? Still in the mountains, he may prefer TH mode. BUT, owner manual doesn't even make that distinction, IIRC.

xo1rider · 10-25-2012, 08:48 PM

Quote:

Originally Posted by Pahaska

I get the best fuel mileage that way and it gives me something to do.

I'm with you, I often manually shift just to keep my hands busy, kind of miss having a manual on this truck other than that not too much to complain about.

dznf0g · 10-25-2012, 08:50 PM

Uggg, I don't want to talk manuals right now. I have a 99 Tracker transmission on the floor of the garage right now. I don't mind fixing stuff, but I'm doing this just to sell it. I'm getting too old for this rolling around on the garage floor manhandling transmissions.

KrazyKelleys · 10-26-2012, 04:53 AM

We just completed a 6 month , 16000 mile trip with my 2007 Classic Silverado 2500 CC 4X4 Duramax LBZ. I towed in every possible terrain. We went from Florida to Pennsylvania, then over to Seattle, down to LA and back across to Atlanta via Colorado, New Mexico etc. I am towing a fully loaded (9700 lbs) Classic 34. Our truck with camper shell was full of stuff. 6 bicycles, 50 gallons of extra fuel in tank in the bed and 6 people ( 2 parents, 3 teen age and 1 ten year old). The whole rig weighed just under 18,000 lbs at the Cat Scales when we left. I averaged between 10 and 11 MPG on the whole trip ( when hooked up, this didn't include driving around w/o the trailer). I hand calculated the mileage with gallons used and the trip meter. I was in tow/haul mode while the trailer was hooked up the entire time. Regardless of the type of terrain we were in. The best mileage I ever got from this truck NOT towing was 18 MPG on a long trip to Texas ( 940 miles one way). I would be curious to know how that stacks up to others on this board. The truck is completely stock and I run 265/75 16 Michelin LTX tires.

KK

TSchleff · 10-26-2012, 06:53 AM

KK ...

I have a 2009 Silverado 2500 Duramax and pull at 30' Classic and normally travel at 65 to 68 mph. It is just my wife and I and we don't have a lot of heavy stuff in the back of the truck nor do we load up the trailer with a lot of stuff either. I have consistently averaged 12.5 to 13 towing the trailer. The absolute worst mileage I have gotten was bucking a high wind and the mileage dropped to a little better than 10. Best mileage towing has been just under 15, when I was basically going down hill, no wind and had to slow down to 55 to 60. Like yourself I hand calculate the mileage of tanks of fuel by using the "gallons used" and trip mileage, which I reset at each fuel stop. (OH .. the "gallons used" is spot on. I normally fill the tank full, full. and I'm never off by more than .2 gallons.) When not towing on the highway we get 17 to 20 mpg depending on speed and conditions.

I also use the tow mode all the time when towing. Around 65 mph it does shift up to 6th gear and I have to be going up a significant hill before it shifts down to 5th.

When we travel we normally go on 3 to 5 week trips which cover 3,000 to 5,000 miles of towing.

Love this truck. But will look at the Ford when it comes time for a new TV.

jchodgdon · 10-26-2012, 07:04 PM

Quote:

Originally Posted by TSchleff

KK ...

I have a 2009 Silverado 2500 Duramax and pull at 30' Classic and normally travel at 65 to 68 mph. It is just my wife and I and we don't have a lot of heavy stuff in the back of the truck nor do we load up the trailer with a lot of stuff either. I have consistently averaged 12.5 to 13 towing the trailer. The absolute worst mileage I have gotten was bucking a high wind and the mileage dropped to a little better than 10. Best mileage towing has been just under 15, when I was basically going down hill, no wind and had to slow down to 55 to 60. Like yourself I hand calculate the mileage of tanks of fuel by using the "gallons used" and trip mileage, which I reset at each fuel stop. (OH .. the "gallons used" is spot on. I normally fill the tank full, full. and I'm never off by more than .2 gallons.) When not towing on the highway we get 17 to 20 mpg depending on speed and conditions.

I also use the tow mode all the time when towing. Around 65 mph it does shift up to 6th gear and I have to be going up a significant hill before it shifts down to 5th.

When we travel we normally go on 3 to 5 week trips which cover 3,000 to 5,000 miles of towing.

Love this truck. But will look at the Ford when it comes time for a new TV.

We bought a 2011 GMC 2500 Denali Diesel last year. We took a trip from Vermont to Florida Keys and return. Used the Tow Haul mode most of the time when hitched to our 28' Safari SO. Average fuel usage was 13.5 total trip. This past summer took a trip w/o safari to Virginia. That resulted in 20.5 mpg. Big difference from my old Suburban 2500, which did no better than 13 mpg empty.

Kosm1o · 10-27-2012, 02:34 PM

I don't mean to hijack this thread, but my 2011 Silverado (gasser) with 6 speed tranny gets the same in or out of tow haul mode. Seeing no advantage, I keep it on.

SL4BLLT · 10-27-2012, 05:33 PM

We use TH whenever under load. Have had no problems on flats at decent speeds. Cannot beat the performance going up or down steep grades such in Boone NC area. We have 130K on the 2005 duramax and still have 52% of the brake pads left with the majority of the use being towing the 31 foot Airstream.

The RPM's do go up coming down the mountain and when I hit the step grades going up it will almost red line if we lose momentum, ie a Prius in front of us in the left lane doing 45 MPH. We end up passing them on the right, now allowing them to get 50 MPG due to no wind in front of them as we are blocking it.

We even have TH on our 2007 Cadillac AWD SRX and at times I will use that coming down those steep grades just to let the transmission do the work and not the brakes as those grades are steep.

Well worth the extra money for the tow packages that were offered at that time.

Howard L. · 11-24-2012, 07:29 PM

Quote:

Originally Posted by xo1rider

I've been towing with the tow haul mode on 100% of the time.

Just curious, when on a flat, straight road at sea level can I or should I turn off the tow haul to reduce RPMs and increase MPG?

There are some great comments on TH and the Allison here. I just put a 2012 3/4 ton Duamax in front of our 30 Flying Cloud. I run it in TH all the time also and I can't see any difference in RPM (TH in or out) once up to cruse. I also don't mind a little more diesel fuel (if there is any to speak of) used when slowing for towns and then accelerating back out again. The engine braking you get going down is also a plus. I would imagine that running the Allison without TH at any time except in the hills, would do no harm either. I just love the truck/engine and transmission combo. Here in TX I set the cruise on at 70 mph and just sit back. It powers up hills with diesel fuel only, no down shift, it just keeps powering forward. Of course, I guess I'm this tickled because I started pulling the new AS 30 with a Chevy 1/2 ton with the 6.2, 403 hp gasser. Should have been plenty of truck, right. Well, not for me. Amazing the shifting that took place in the hill country area of TX. Plus in mid summer at 105 degrees, if you didn't let it slow going upgrade it tried to overheat TH in or out. You had to use TH in the gas hog if you wanted to accelerate with any authority at all.