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Discussion Starter #1
First, I realize there may be no absolute answers for my questions. I am looking thoughts from person past experiences.

Last April we pulled our travel trailer (7000 pounds plus several hundred extra pounds of equipment) to Fayetteville, AR. We tow with an 06, crew cab, 8 ft.bed, 4 wheel drive, with around 350,000 miles on it now. The towing capacity for this truck is listed at 12,000 pounds.

Towing through mountains on interstate highways, the truck would slow down to 45 - 40 mph - if I did not force it to run harder. We were being pasted by other trucks (gas / diesels) pulling similar size rv's.

I watched the tranny temps go just above 200, and engine temps go just above 210. Of course things cooled off downhill. Since then I have pulled the pan off the tranny to change the internal filter and found the bottom of the pan fairly clean - there were no large, if any, build ups of materials in the bottom of the pan.

So, my question is, did I need to go so slowly? Would it have damaged the truck / tranny to "force" it to go faster? Is the tranny geared to handle such weights at higher speeds? How high can the tranny / engine temps run when pulling loads?

We are contemplating another trip to AR, but not under the above conditions. Sorry this is to long, just trying to provide as much info as possible. Any thoughts are appreciated. Thanks much - Kip
 

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Thread relocated over to "Towing" for more appropriate answers to your questions

:thumb:
 

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Davester may be on to something

The short version is that leaves, pine needles and all kinds of other stuff that you expect to find on the shore of a river can get stuck between the intercooler and the radiator, and it blocks air flow to everything. That's what's considered the cooling stack. If you can get them apart and clean all the gunk out you may have a lot better air flow, which will allow the tranny cooler to function better, the radiator to function better, and your intercooler to function better. you can search 'cleaning the cooling stack' on here and find a couple good threads about how to do it.

Do you park the truck outside?

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Thanks for the help thus far. I did clean the cooling stack prior to our trip. I sprayed diluted Purple Power into the front of the stack, waited and rinsed. It did clean out a lot of dirt. I removed the front grill and top piece to do this.

Yes, the truck sets outside, so I am mindful of falling leaves and such...

My greatest concern was it's slowing to about 45 up inclines. I was reluctant to "force" it to go faster, for concern of over doing it, and causing some type of damage, that would leave me on the side of the road.

Several YouTube people have mentioned dropping the truck into the next lowest gear. I use the tow mode of course, and have always left it in Drive - dropping it into a lower gear doesn't seem to make sense. Seems the tranny should know what to do on its own. Thanks - Kip
 

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Your truck has self-protect mode. If anything gets too hot it'll derate the power output and restrict the transmission to lower gears. IIRC, the fan doesn't even come on until 225*. Use tow-haul. Let the truck do it's thing. If you don't like the tranny temps, get an auxiliary transmission cooler. Tons on here about that.

Allison 1000:

The*2004.5-2010 LLY, LBZ, & LMM:*These transmission will run a higher normal operating temperature than the LB7 models. Normal operating temps will range from 180-200 approx. 100 degrees above ambient air temps. These transmissions will run from 200-230 in the summer months when towing in hilly areas. These temps are normal and will not hurt the transmission. If you are seeing temps above 235 degrees on a regular basis you should check your fluid level. Fluid levels to high may cause excessive temperature. Higher mileage transmissions or trucks using aftermarket tuners with increased power may be experiencing converter slippage and will see increased heat.

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You can see in my signature that I've addressed a similar issue. Run the deep pan and extra fluid. It's not just the extra fluid, but you can run the fluid lower and keep it out of the moving parts, where it additionally heats up. Get a Mike L cooler. Run a TES 285 fluid, which will allow you to run at 220 all day. But 210 is not hot. Make sure license plat is not positioned to block air intake. You can also invert trans fluid cooler. Search DP for these issues. A lot has been written. BTW, running too slow (below about 30 mph) prevents trans lock up and makes for fluid heating. Newer Allisons have addressed the heating issue. And Roswell is correct, fluid level too high will cause heating.
 
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When checking the tranny fluid, make sure its at operating temp in gear and near the bottom of the hash marks.
Check the radiator inlet line connection from the tranny. See if any debris is blocking the inlet. Take an infrared laser gun and check the temps on the tranny cooler pre and post.
 

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Discussion Starter #9
Thanks so much for the help. I'll check the fluid level in the tranny - I am pretty sure it is higher than the bottom hash marks. I'll clean out the cooling stack again and look into an extra tranny cooler. Thanks again - Kip
 

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Thanks so much for the help. I'll check the fluid level in the tranny - I am pretty sure it is higher than the bottom hash marks. I'll clean out the cooling stack again and look into an extra tranny cooler. Thanks again - Kip
If I actually towed more I'd have the Mike L cooler, the deep pan, and maybe a Transgo Jr. Known commodities.

Best of luck,

Roswell

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Do you have an EGT sensor? that is what I would be going by for towing temps. When mine hits 1300degs I start to back off a little. anything below that should be good. 1400 is ok for a very short time, but not a sustained run.
 

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I never tow anything very heavy in 6th gear. I pull in 5th with tow haul on. Most likely you are lugging it and with you light footing the pedal it won't downshift and the engine is working overtime
 

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I have an 07 classic 3500. Duramax/Allison I pull my toyhauler- fully loaded at 16,875lbs. I like to run about 60-65mph. Trans and engine temps have been as high as 250, that's when I let it cool down a little. The only thing I've ever seen on my DIC is a warning that read "Turbo overboost" Don't know what it meant, but I let it cool down and kept moving. That was 3 years ago.
 

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Your temps aren't high. I'd have been standing on the pedal. What do you mean force it to go faster? You mean give it enough throttle to climb the hill? Yes, by all means give it some more throttle so it will go faster. My '05 LLY has 261,000 miles on it. I wouldn't be worried until the temps for both trans and engine got up to 230 or maybe 240 for a short duration up a hill. Mine's been hotter than that briefly several times with no damage done.
 
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Your temps aren't high. I'd have been standing on the pedal. What do you mean force it to go faster? You mean give it enough throttle to climb the hill? Yes, by all means give it some more throttle so it will go faster. My '05 LLY has 261,000 miles on it. I wouldn't be worried until the temps for both trans and engine got up to 230 or maybe 240 for a short duration up a hill. Mine's been hotter than that briefly several times with no damage done.
"Your truck has self-protect mode. If anything gets too hot it'll derate the power output and restrict the transmission to lower gears. IIRC, the fan doesn't even come on until 225*. "

Thanks so much for the help. I have never had a diesel truck before and there is still much to be learned. I am not sure what the "self-protect mode" is and what it does and what activates it... how does it "derate the power output and restrict the tranny"? Not sure what "IIRC" is,but I am assuming it controls one of the fans.

I also assume that driving the truck in 5th gear, means using the "M" transmission positions... What is the effect of using this gear as apposed to using Drive and letting it shift into 6th? How does this impact the truck's abilities? Its cooling and such?

We are planning another trip to AR in July or August, thus this is all very helpful. Again, thanks so much for the help. kip
 

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"Your truck has self-protect mode. If anything gets too hot it'll derate the power output and restrict the transmission to lower gears. IIRC, the fan doesn't even come on until 225*. "

Thanks so much for the help. I have never had a diesel truck before and there is still much to be learned. I am not sure what the "self-protect mode" is and what it does and what activates it... how does it "derate the power output and restrict the tranny"? Not sure what "IIRC" is,but I am assuming it controls one of the fans.

I also assume that driving the truck in 5th gear, means using the "M" transmission positions... What is the effect of using this gear as apposed to using Drive and letting it shift into 6th? How does this impact the truck's abilities? Its cooling and such?

We are planning another trip to AR in July or August, thus this is all very helpful. Again, thanks so much for the help. kip
How are you driving the truck? Cruise control on or off? How are you forcing it to go faster up the hills?

IIRC means if I recall

With that load on the truck you should have no issues holding speed going up hills. My 06 when it was stock was great in the mountains with a load I always used my cruise and let the truck do the work.

I've done 70+ in the desert with the 06 in 110 degree heat. Trans temps where about 230 and the engine temps actually climbed high enough to kick the fan on gauge was about 250 and the fan cooled the temps back down.
 

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"Your truck has self-protect mode. If anything gets too hot it'll derate the power output and restrict the transmission to lower gears. IIRC, the fan doesn't even come on until 225*. "

how does it "derate the power output and restrict the tranny"?

REDUCED ENGINE POWER This message is displayed when the cooling system temperature gets too hot and the engine further enters the engine coolant protection mode. See Engine Overheating on page 502 for further information. This message will also display when the vehicle’s engine power is reduced. Reduced engine power can affect the vehicle’s ability to accelerate. If this message is on, but there is no reduction in performance, proceed to your destination. The performance may be reduced the next time the vehicle is driven. The vehicle may be driven at a reduced speed while this message is on, but acceleration and speed may be reduced. Anytime this message stays on, the vehicle should be taken to your dealer for service as soon as possible. (2007 Classic Owner's Manual, pp. 237-238)

TRANSMISSION HOT Notice: If you drive your vehicle while the transmission fluid is overheating and the transmission temperature warning is displayed on the instrument panel cluster and/or DIC, you can damage the transmission. This could lead to costly repairs that would not be covered by your warranty. Do not drive your vehicle with overheated transmission fluid or while the transmission temperature warning is displayed. If the transmission fluid temperature becomes high, this message will appear on the DIC display. When the transmission enters the protection mode, you may notice a change in the transmission shifting patterns. When the transmission fluid temperature returns to normal, the display will turn off and the transmission shifting patterns will return to normal. If the vehicle has the Tow/Haul mode, use this feature if the transmission is operating at higher temperatures and/or the following situations exist, which can cause the transmission to operate at higher temperatures:
• Towing a trailer
• Hot outside air temperatures
• Hauling a large or heavy load
• Over-loading
• Low transmission fluid level
• High transmission fluid level
• Restricted air flow to the radiator and the auxiliary transmission oil cooler (2007 Classic Owner's Manual p. 277)



Not sure what "IIRC" is, but I am assuming it controls one of the fans. Google says



Again, thanks so much for the help. kip
You should have gotten both an Owner's Manual and a Duramax supplement with your vehicle. They are very informative. If you don't have them, the supplement can be found here and the 2007 manual here, or you can Google for a 2006 if you prefer. It really doesn't matter though. I'd suggest familiarize yourself with the transmission section pp. 140-149. Towing is covered staring at p. 423.
 

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Discussion Starter #18
Thanks for the help. I'll check the truck for it's owner's manual. I don't recall one when I purchased it. If not, then I'll go on line and read up on the tranny and towing! Again, thanks - kip
 

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So, the owner's manual was less than helpful. It offers general information. But failed to answer my questions. Let me try here:
1- does it hurt the tranny while towing in hilly areas to shift from Drive into Manual, and perhaps back into Drive again? (Not continuously back and forth of course) Towing up and down hills - I assume the best practice is to Tow Mode and 5th gear in Manual operation.
2. From other comments, I am also assuming that while towing in Tow Mode in 5th gear, it is OK, or even better to "force" the truck to cruse up the inclines maintaining decent speeds.
3. Temp's - It is OK, to allow tempts on tranny and engine to increase, but not into "red" or danger areas obviously.
4. Tire pressure - I also read that tire pressure when towing should be at the max cold psi as indicated on the tire. (mine state max psi is 80 - I fill the rear to 75 - 76, and the fronts about 72'ish. I do have a load stabilizing (right term?) hitch which transfers some weight to front.
I think that's about it. Thanks for the help - we may head to AR again this August and I hope to get this figured out before then - thanks
 

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When you use the M trans function, you are limiting the highest numerical gear to the selection, i.e. 5 = max 5th gear, 4 = max 4th gear etc. So when towing 5K or more use tow haul. And I have found that using 5th gear vs 6th gear, there is almost no discernible mileage difference. Shift at will, but don't wear your arm out doing it. If your engine temps rise above 220, go to a lower gear, more rpms.

Keep in mind when you are talking about 'inclines', everyone reading your questions or comments has a different opinion about what an incline is. May be a 5% rise, maybe 2%, or even 10%. And they could be of varying lengths and slope and length must be considered when deciding gear, rpm, etc. So it is always best to better describe your incline.

Rear tires at max, fronts 70 or more is my rule.
 
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