Towing speed up 6% grade

[rrh13441]

I have a 2012 GMC 2wd 2500hd LML with firestone airbags, fully deleted towing a 2017 GD 348m with a max weight of 16500 5th wheel. Fully loaded I’m weighing in at about 16k. I tow in the mountains of AZ with lots of 6 to 7% grades and usually I’m in manual mode , 3rd gear @ 3200 RPM speed around 40 mph. My temp reaches max about 220 to 225 on hot days. I see other Duramax trucks pulling a big 5er and they go right by me. Is 40 mph pulling steep grades with this big 5er about normal for a 2012 2500hd Duramax?


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[DAVe3283]

That doesn't sound out of the ballpark, but if you haven't cleaned your cooling stack in a while, it might help.

The other thing is if the fan clutch is original, it might be getting weak. I know they are electronic on the LML, but I think they just run a heater to help the fan engage when needed, and if the viscous fluid leaks out, it can't fully turn on. It might be worth trying to read the fan RPM on a scan tool, and if the fan isn't fully engaging, throw a new clutch at it. You can also just listen to it. The fan should be making a LOUD roar, especially at 3200 RPM, if it is fully engaged.

 

[NevadaLLY]

I tow a 42' weighing in up at 20K and pull most of the grades at 65 so long as temps all stay happy. BUT look at my signature. That's why trucks like mine or other Duramax are passing you - they've added/modded and most of us don't flaunt it on the outside. Before the big goodies on my truck, 40 all day on those slopes in the heat.

 

[Ron Nielson]

I tow in the mountains of AZ with lots of 6 to 7% grades

Are you talking about I17 between Phoenix and Flagstaff? US 87 between Phoenix and Payson? Trying to better understand the roads you are talking about.

I've driven both of those roads many times pulling my 12K 5th wheel and I use tow haul, 5th or 4th (or even 3rd) if someone slows me too much. You are 4K heavier and that is quite a bit more load. Generally, I'm looking for at least 55-60 and not pushing the truck too much. I could go faster if I wanted, but why? It only lasts for a few minutes. I'd rather slow a little vs being on the side of the road with an overheated engine.

Like the other posts said, make sure your cooling stack is clean and that your fan clutch firmly engages such that you hear a roar. No roar? replace the fan clutch if the connections are good and working properly.

 

[1FastBrick]

@Chevy1925 would probably know this area and what these trucks are capable of on that stretch of highway

 

[Chevy1925]

lol slightly.

220 to 225 in our temps is awesome. I doubt you have a cooling issue.

Will it just not hold 4th gear? I’d 16k in weight including the weight of the truck? Might have some weak tuning going on OR something is not letting the truck make power and it’s pulling back on it. How many miles do you have on your truck?

 

[rrh13441]

lol slightly.

220 to 225 in our temps is awesome. I doubt you have a cooling issue.

Will it just not hold 4th gear? I’d 16k in weight including the weight of the truck? Might have some weak tuning going on OR something is not letting the truck make power and it’s pulling back on it. How many miles do you have on your truck?

My tune is set stock, use tow mode with exhaust brake on. I do not use cruise I use manual. I have a new huge radiator, intercooler, water pump, cp3 conversion, EGR deleted. I think it’s weight. My dry trailer weight is 13k the GVWR of the trailer is 16500. With my SXS, 117 gal of water, all the food and gear I’m pushing 15k. I have 150k on my truck.


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[Chevy1925]

My tune is set stock, use tow mode with exhaust brake on. I do not use cruise I use manual. I have a new huge radiator, intercooler, water pump, cp3 conversion, EGR deleted. I think it’s weight. My dry trailer weight is 13k the GVWR of the trailer is 16500. With my SXS, 117 gal of water, all the food and gear I’m pushing 15k. I have 150k on my truck.


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Ok so you are talking trailer weight, not 16k including truck weight.

Have you tried bumping up the tune and running it? I still feel you are on the weaker side of what you should be seeing for speed. I’d expect 45-50mph.

For instance, my 2020 up camp verde hill headed back to phx (assuming I don’t slowed up by traffic) will hit 56-57mph at the slowest. I gross around 26-27k with my toy hauler and tracker in the back of it (this includes truck weight). Truck is 100% stock.

I know of lots of LML trucks that gross around what you are at and they are moving up the hills faster.

Just fyi, that fan won’t come on full bore till 230* on the coolant temp. I would not worry about that temp. 235-240* sustained (fan full bore and temps not coming back down), I’d start pulling back on the throttle. Turn the power up and see what it does.

 

[1FastBrick]

I figured if anyone was qualified to answer his question, Especially in that region, You would be the man!!!

 

[rrh13441]

Ok so you are talking trailer weight, not 16k including truck weight.

Have you tried bumping up the tune and running it? I still feel you are on the weaker side of what you should be seeing for speed. I’d expect 45-50mph.

For instance, my 2020 up camp verde hill headed back to phx (assuming I don’t slowed up by traffic) will hit 56-57mph at the slowest. I gross around 26-27k with my toy hauler and tracker in the back of it (this includes truck weight). Truck is 100% stock.

I know of lots of LML trucks that gross around what you are at and they are moving up the hills faster.

Just fyi, that fan won’t come on full bore till 230* on the coolant temp. I would not worry about that temp. 235-240* sustained (fan full bore and temps not coming back down), I’d start pulling back on the throttle. Turn the power up and see what it does.

Just curious when driving what parameters (gauges) should I be monitoring on my H&S MiniMax Tuner?.
I monitor the load and temps and found that if I keep the load between 50 and 60lbs all is good. if I go above 60 lbs on my load I get an increase in temperatures. In keep in that load zone I can pull steep grades but at 40mph max and 2nd gear. What gauges do suggest monitoring on the tuner to get best performance? And at what degree should I start to be concerned with temperatures, turn off AC or pull over to cool down when towing?


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[Ron Nielson]

And at what degree should I start to be concerned with temperatures, turn off AC or pull over to cool down when towing?

Look at the antifreeze concentration in your cooling system, then get the boiling point for that concentration on the internet. Then factor in the 15 lb pressure cap on the coolant system. That should give you a red line where your troubles may become very difficult difficult. The thing that I keep foremost in my mind is that as long as the fan clutch is locked and pulling max air thru the cooling stack and the temp is fairly constant, I'm pretty happy just continuing to drive. If I see a spike in the temp when it is at the max, I quickly become very concerned, raise the rpms by downshifting, back off the throttle even more, turn off the AC, etc, BUT I don't shut off the engine, just remove the load from the engine. If I stop, pull off the road, I keep that engine running because the heat will spike even more if it is turned off and very well may boil. Once it gets down to say 220, it has cooled enough that I am no longer concerned. And don't remove the coolant cap on a hot engine. You immediately drop the pressure, which drops the boiling point, and that is to be avoided.

 

[2004LB7]

I wait until the hot engine message come on the DIC. Then I back off or pull over

 

[Chevy1925]

Just curious when driving what parameters (gauges) should I be monitoring on my H&S MiniMax Tuner?.
I monitor the load and temps and found that if I keep the load between 50 and 60lbs all is good. if I go above 60 lbs on my load I get an increase in temperatures. In keep in that load zone I can pull steep grades but at 40mph max and 2nd gear. What gauges do suggest monitoring on the tuner to get best performance? And at what degree should I start to be concerned with temperatures, turn off AC or pull over to cool down when towing?


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Load isn’t going to reference much to us just watch oil pressure, coolant temp, egt, see if you can see fan rpm and run it like I was saying before. I think you are cutting yourself short because you have not let the fan fully kick in due to fear of a coolant temp that isn’t an issue yet