Towing in overdrive

[Diamondpilot]

I just returned from an atv riding trip in Logan WV {Hatfield McCoy trails}. I rode with a friend who has basicaly the same truck as me, other than the fact that his truck has the 8100 gas engine with an Allison and 4:10s, 2wd, mine is a DMax Allison, 3:73, 4WD. Both trucks have 265's, are reg. cab long beds, and relatively close miles, mine 97k, his high 80's, his is a 2002 2500HD, mine is a 2003 2500HD.

We were towing a 22ft tailgator camper/toy hauler with 2 4wd utility quads inside, and gear and food for four adults, the water and waste tanks were empty, we estimate the weight of the camper to be around 6500lbs as towed. We were also using a cab top air deflector. The best hand calculated MPG we got was 7.1mpg, the rest of the time we were between 6.4mpg and 6.8mpg. It was 392 miles each way, and it took almost 3 tanks of fuel to get there and about 2 and a half to get home[ had a little left]. The Rig also spent lots of time in second gear at 4000+ rpm's climbing the hills on the freeway, it did however maintain 65mph the entire time, regardless of the terrain.

It would have been cheaper to drive my Duramax down there by myself {towing the same load], rather than splitting fuel with my 8100 buddy. I also doubt that it would have come out of overdrive on any highway grade that we encountered, [it is chipped though] based on past mountain towing experience in it. I sure am glad I spent the extra money 6 years ago for a diesel. The 8100 did the job, but I prefer the diesel.

I always tow in overdrive, and use Tow/Haul when towing and NEVER exceed 60hp setting on the chip when towing. Rarely have I seen trans temps in excess of 200 degrees, only a couple times when towing in heavy stop and go highway traffic. My buddy with the 8100 towed all the way down and all the way back in tow haul overdrive with no issues. That being said, If I did not have a Allison, Torqueshift, or Aisen, I would play it safe and keep it out of overdrive when towing, as none of the older auto OD's [E4od, 4l80 etc.] were realy made to be towing in OD.

Great real world numbers. Like you said your diesel would have done a easy 12mpg and probably much better. My neighbor has a Classic 2007 3500 Long Bed 4x4 Dmax and pulls a 14K 36' GN and gets 12mpg pulling it. I know the trailer has more drag but I get right around 9 pulling my 7,000# boat with my Titan which has a 5.6L engine, something around 320 HP and 395 FT LB TQ and 4.10 gears. It will run 70 with the tow haul mode on and stay around 2,000 rpm. The 9mpg has been true in both stop and go and the 2 800 mile trips I have taken with it this summer.

Chris

 

[herd]

This has been an interesting and informative thread. I just got into camping (at my wife's insistence) this year and bought a 28' travel trailer (32' bumber to tongue). How little did I know about towing, pulled it home with my 2001 Silverado 5.3L truck, found out right away that the TT was too much weight.

Went shopping for a good used 3/4 ton used truck, found out diesels with low mileage and reasonable priced are two different things; they all had either high miles/lower price or low miles/higher price. So ran across a 2002 Sierra 2500HD with the 8.1L gas and Allison tranny and only 37,000 miles, at $12k.

Truck pulls camper great but I can't figure out which gear/mode that I should cruise in. I made a trip to the mountains in VA and was in tow/haul mode until I got to a very steep and long grade (going up). Truck downshifted and even tho turning 4500 rpm's, it would not do over 45 mph. That plus a horrendous loud roaring noises. I pulled over, took off town/haul, and proceeded on. I found out that in the "D" selection and without tow/haul, I could pretty much maintain 2000 rpm's and 60 mph except on very steep hills. There I just built up speed going down and usually pushed up to 3000 rpm's near the top of the hills. Seemed like much less strain on the engine and tranny that way.

Now I am totally confused on how I should tow on flatter land. Tried towing in tow/haul and "D" on a recent coastal trip. The truck did ok cruising but on minor grades, it would shift down and run up the rpm's while taking what I thought was too long to come out of it. Then, in town, as I approached my stops, the trans would downshift heavily and really sounded like it was in a strain.

Back on the road, cruising without the tow/haul, I did not have these problems. So, my question is, is this normal operations for the Allison? Is this downshifting of the tranny and up powering of the engine to the 4000+ range ok? What about the "rough shifting" at times?

Even tho this is an '02 model, the previous owner did not service the Allison since he was nowhere near the 50,000 mile mark. I thought I might go ahead and get it service although the fluid looks and smells normal.

One other thing, on the trip in the mountains, I was running around 190-200 degrees on the trans. On the coastal trip recently, I ran as high as 211 degrees (it was 100 degrees day tho).

Since I am a novice at this towing thing, any help or advice will be greatly appreciated.

 

[Builder]

The roaring noise may have been your cooling fan coming on.

You may have not even needed tow haul because your trailer isn't heavy enough, but I don't know your trailers' weight. If you read your owner's manual, it will tell you that if you use tow/haul when lightly loaded, you will experience unsatisfactory performance. It will downshift more harshly or at intervals you may not like.

I think if your truck has ~40K on it, it would be a good idea to flush & refill. Use "Transynd" this time around. It's what the allisons in medium duty trucks use. Runs a little cooler and lasts 50K miles.

Other than the previous owner selling you a truck with transmission abuse or failure, you bought the best automatic transmission on the market today.

 

[herd]

Builder, tks for the info, I did not realize that use of tow/haul on lighter loades would produce a problem. The truck is rated for 15,400# towing capacity, the trailer is right at 10,000#. I do not know at what point divides "light weight" and "heavy weight" but I assumed that the trailer was heavy enough for "tow/haul." Maybe I was wrong.

I do not think (or want to think) that this transmission has been abused. I mean the truck is immaculate, almost showroom condition, even still a little new smell. The previous owner, a 78 year old well-off gentleman, was meticilous with this vehicle, as well as his house and other property. That aside, how could I verify if there's been abuse or if this tranny needs help. I surely do not want to get stranded and I was hoping to do some "out west" camping in the not too distant future.

 

[Builder]

Builder, tks for the info, I did not realize that use of tow/haul on lighter loades would produce a problem. The truck is rated for 15,400# towing capacity, the trailer is right at 10,000#. I do not know at what point divides "light weight" and "heavy weight" but I assumed that the trailer was heavy enough for "tow/haul." Maybe I was wrong.

Not many owners do know that. A lot of guys complain about tow haul when lightly loaded, but you aren't lightly loaded, so you're legit. I don't use tow/haul all the time until I go over 8-10K or I'm on hilly ground. Still your tow/haul should be fine to use with your trailer. The shortest way to resolution would be to hook up the trailer and have a allison tech jump in with you for a ride. Heck, you could be low on fluid, need a new spin on filter, etc.

I do not think (or want to think) that this transmission has been abused. I mean the truck is immaculate, almost showroom condition, even still a little new smell. The previous owner, a 78 year old well-off gentleman, was meticilous with this vehicle, as well as his house and other property. That aside, how could I verify if there's been abuse or if this tranny needs help. I surely do not want to get stranded and I was hoping to do some "out west" camping in the not too distant future.

It probably wasn't, but you shouldn't have those problems, either. I don't have any problems like that and nobody else I know that owns one does, either. Except for diamond pilot-everything broke on his HD.

 

[Diamondpilot]

One other thing, on the trip in the mountains, I was running around 190-200 degrees on the trans. On the coastal trip recently, I ran as high as 211 degrees (it was 100 degrees day tho).

Since I am a novice at this towing thing, any help or advice will be greatly appreciated.

Even though I am a Ford HD guy you did good buy buying a larger truck. The big gas engine will suit you fine for your occasional towing.

When should you change the tranny fluid? Now. If it got over 200 deg you need to change it. The rule of thumb is 200 deg max on the tranny temp.

Chris

 

[Bird]

The roaring noise may have been your cooling fan coming on.

It's been a long time since I heard that roar. I had a cousin with me once in my 1989 Chevy towing my 32' fifth-wheel and when that roar came on, going uphill, he said "Uh, oh, there went your transmission." He thought it was an rpm increase; slipping transmission.

 

[jayste]

I agree with Builder on the fan issue. I'm thinking the truck was sensing the need for extra cooling and the fan kicked in. I'm not familiar with the GM 8.1/Allison set up but my 7.3 PSD/6 speed set up has a very noticeable fan when the temps get right.

Jay

 

[Builder]

When mine came on in my Powerstrokes, it would scare the crap out of you.

 

[herd]

QUOTE:"When should you change the tranny fluid? Now. If it got over 200 deg you need to change it. The rule of thumb is 200 deg max on the tranny temp."

Chris, you say this is a rule of thumb and I agree, most good tips/info usually are from experienced rules of thumb but, I looked it up in the owner's manual and it said that up to 260 degrees was normal operating range.