First towing impressions and a few questions

skav · January 1, 2015

So I've had my 2500 ccsb since sept. I love it and drive it every day but up until last weekend I've only pulled my boat to a local lake.

Boat and trailer are about 6500lbs so it pulled without issue.

We loaded up the toy hauler last Friday and headed out to the desert for a few days. This was the test I was waiting for. The trailer loaded is 15-16k. I have a 17k weight distributing hitch I use with the trailer and I added air bags when I bought the truck.

We stayed in Cal City which is about 100m from the house and there were a few grades that let me compare it to my past trucks, a Dodge 2500 twin turbo 24v (450hp) and a Ford F-250 w a built 7.3 (550hp).

Both pulled well in tow settings but EGTs, coolant and trans temps were always the limiting factors when pulling grades.

My hopes were high with the 6.6 and the Alison, but I was a bit worried that I'd be let down.

I clicked the tow and exhaust brake as I pulled away from the house and set the brake controller at 7.0.

I left it in drive and got on the freeway and up to speed quickly. The back end seemed to move around a bit and bounce more than expected but I figured that was because I only had 45psi in the bags. (I ran the bags at 55psi on the way home and it made a huge difference.)

Braking and slowing was great with the controller and exhaust brake. Way better than the Ford or Dodge.

20m into the trip was the first decent grade. It starts at 1,500' and climbs to 3,225' in 11m.

I was still figuring out the truck so left it in drive. It pulled well but I had my foot in it to hold 60mph. It wanted to stay around 1800rpm. About half way up the grade I shifted into M and dropped it into 4th gear. This brought the rpms to around 2300 and it pulled better. Once on the flattish ground I set cruise in 5th and it cruised at 70mph no prob.

I loved the 6 speed trans and smooth power. Everything was very smooth and controlled.

So here are a few questions after towing for the first time.

1. What's the best rpm to pull a grade with? There are no boost/egt/ trans gauges so I can't keep track of those but I feel that pulling a grade at 1800 is too low.

2. Is there any issue leaving the exhaust brake on all the time when towing?

3. What else do I need to know about when towing w a Dmax?

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doverarjim · January 1, 2015

I use exhaust brake all the time, the truck is my dd so when I hit the key my right hand hits the brake button and then grabs the shifter and I am off. As far as best rpm I let mine do its on thing, the computer in it is a lot faster and smarter than I am. I put the Tow / Haul button get it up to the speed I want hit cruise and set back and watch the miles go by. The only time I make much input to what is going on is when we are in rolling hills/mountians where the engine brake is slowing me down going down hill and as soon as we bottom out it will start climbing again, I will keep the speed up to make it easier to get up the next hill/mountian. If you feel the need to check on trans temp you can flip thru the DIC and it shows that temp. I have not owned any other diesel but coming from the Chev 6.0 to the Dmax it was the best move ever!!

skav · January 1, 2015

Thanks for the reply. I got to play w cc a bit on the way home. We took a different route that had probably 20m of down grade. I set cc w the exhaust brake on and just chilled. It worked very well.

Another really nice bonus was that the trailer was still clean when we got to the desert. The other trucks would blow soot when taking off or accelerating. Also, power seems super smooth with the Dmax. I didn't get any axle wrap or wheel slip. I think that has a lot to do a the traction control. It just has power and no slip. Very cool.

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Caleb 6R · January 2, 2015

I did alot of towing this summer with the race team. about 15,000 kms all over eastern and central Canada. I'm about 10,000lbs loaded with trailer, gear and guys. I just hit the highway, set the cruise and steer. This truck makes things easy, when in cruise control and tow haul on you need not hit the exhaust brake button. it will be activated as nessecary to hold speed on declines. I found in tow haul, and cruise the truck wouldn't let the speed vary more then 5 km/h. We have a few big grades here from sea level into the apalanchain mountains, but noting more then a few kms long. Never once set manul mode and left it in 5th, again letting the truck do it all. At 105 km/h i was getting 12-14 mpg depending on grades. and approx 12 mpg at 120 on flat gorund, all hand calculated. Best purchase i made for the team all year.

Caleb

skav · January 2, 2015

I did alot of towing this summer with the race team. about 15,000 kms all over eastern and central Canada. I'm about 10,000lbs loaded with trailer, gear and guys. I just hit the highway, set the cruise and steer. This truck makes things easy, when in cruise control and tow haul on you need not hit the exhaust brake button. it will be activated as nessecary to hold speed on declines. I found in tow haul, and cruise the truck wouldn't let the speed vary more then 5 km/h. We have a few big grades here from sea level into the apalanchain mountains, but noting more then a few kms long. Never once set manul mode and left it in 5th, again letting the truck do it all. At 105 km/h i was getting 12-14 mpg depending on grades. and approx 12 mpg at 120 on flat gorund, all hand calculated. Best purchase i made for the team all year.

Caleb

Nice info. I'll set cruise going up the grade next time and see how that works.

My mileage was 8.6mpg there and back.

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Caleb 6R · January 2, 2015

sorry, when i say loaded, i;m not including the wieght of the truck. I haul a 8.5x24 UXT car hauler and use a truck cap to get the wind over the trailer. So that helps alot as well.

DenaliDually · January 4, 2015

I use exhaust brake all the time, the truck is my dd so when I hit the key my right hand hits the brake button and then grabs the shifter and I am off. As far as best rpm I let mine do its on thing, the computer in it is a lot faster and smarter than I am. I put the Tow / Haul button get it up to the speed I want hit cruise and set back and watch the miles go by. The only time I make much input to what is going on is when we are in rolling hills/mountians where the engine brake is slowing me down going down hill and as soon as we bottom out it will start climbing again, I will keep the speed up to make it easier to get up the next hill/mountian. If you feel the need to check on trans temp you can flip thru the DIC and it shows that temp. I have not owned any other diesel but coming from the Chev 6.0 to the Dmax it was the best move ever!!

I'm with you... I use the exhaust brake all the time. I wish it would remain on if set on the prior trip like my Ram. Wonder if someone has figured a mod with diodes like the fog w highs or the mirror lights with reverse?

Something worth mentioning is how the system works. Some don't use it correctly. All you have to do is press the brake pedal enough to engage the brake light for a second, after that if in tow/haul, it will do the rest. I generally only "use" the brakes once below 10 mpg or if a jackass cuts me off.

These trucks are smart enough to do it all for you. It's kinda like those infomercials for that oven thing, set it and forget it. My 2015 denali has a sweet feature that bring all the Temps up automatically when I press tow/haul. So I monitor them but even at 36k combined, in Florida, my trans temp hardly is affected.

As far as cc. I just ran to the mountains in Colorado with that 36k, cruise set the whole way. No more manual shifting. As a pilot I'm use to always adjusting, monitoring, tweaking.... no more. Lol. Kinda boring. Now I just surf xm channels. It chooses the perfect gear and holds it. No weird rpm zones at all like my ford.

And as far as mpg, 36k was getting about 6.5. I hadn't installed a aux tank yet so 170 miles per tank was it on that trip. Can't complain bc of how over loaded it was really. Most of my other setups scale in at around 20k to 28k and I'm usually around 8 mpg with them.

My 2014 ram drw gets 2 mpg (avg) better under load but WONT get better than 12 empty. My denali is my daily driver so it works out.

Hope this helps.

Cowpie · February 7, 2015

RPM's factor a lot with EGT's. If EGT's are climbing excessively, need to bump the RPM's up and get exhaust flowing faster. EGT's should be lower and engine should run a tad cooler also. There is a point, when you are working a diesel and putting a strong load on it, that too low RPM can create a scavenging effect in the exhaust. Exhaust flow is cooling too fast in the plumbing and reduces flow and creating restriction, wherefore exhaust can't be pushed out the cylnders and manifolds quick enough before they generate higher EGT's. Bad enough that the emissions stuff is no help. This becomes as much an art form as it does science. The engineers is programming shift points on the trans are more for averages. You have to think for it once in a while. Drop a gear on a hard pull and get the RPM's up some more and see if that doesn't help. Should be easier on the trans temps as well.

redwngr · February 12, 2015

Those that tow heavy and frequently and report on the duramax forums all recommend to set the exhaust brake and the cruise and let the truck to the work.

It is smart enough that it will not hurt itself.

EllerClanDad · March 5, 2015

I pull a 40 ft 5th wheel with 3 slides. It is heavy, I have a RZR in the garage 150 gal of water, 40 gal of gas. I am close to 17k going down the road. I ride nice and level without air bags (I was surprised and happy about that). But it pulls and handles downhills with just setting the brake controller to 6.0, and engaging the exhaust brake. All I have to do is keep it between the lines which is a snap. I love this truck. So much more pulling power and braking action than my 2004 had.

2TrakR · February 14, 2016

On my 2012, our 41' toyhauler fifth wheel pulls great. We added bags to the back to level the truck. CAT scales put us a shade over 24K combined, normal load.

To the OP questions, my experience:

1. Let it shift and do it's thing.

2. I run the exhaust brake all the time (have issue with my 16 and cruise control, but that's a different story).

3. Less fiddling, the better the truck works. I tow a variety from the fifth wheel to tri axle w/dozer to smaller enclosed trailers.

Flip on T/H and set the cruise.

I will shut off the cruise, like others have mentioned above, when there is a lot of up/down as the truck will do it's best to maintain downhill speeds and if you have another uphill coming soon, it's going to also do what it can to hold speed going up the next one including downshifts as necessary. I run the speed up going down so you coast up the next one a bit more.

Bigger climbs, stuff like Rarity Mountain on I75/TN I will take it out of cruise and play to run at a speed I'm comfortable with going up. With the 5th wheel I can hold 60 without screaming too many RPM on the way up. I've not found where manually running the trans made any help over leaving it in D.