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Old 09-09-2011, 01:02 AM   #1
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Question Towing a 4900 lb SUV Over The Mountains

I have a 2010 40' Diesel Pusher (350 Cummins) and was towing a Buick Enclave (4900 lbs) through the Smokies. Top Speed going up the mountains was 25 mph. The highway was 2 lanes and couldn't pull over to let the 50 cars behind me pull ahead! The average grade was 9 degrees. The question I have is this maximum speed under the towing conditions normal? is there anything I can do to pick it up, i.e. run in a different gear?

Jim's Discovery
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Old 09-09-2011, 03:43 AM   #2
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Jim, sounds like you need to manually shift your transmission to keep you engine RPM some where between 1800-2000. By manually controlling the transmission it will keep you in the power band of the engine, and keep the water temp down as well. However if your coach is fully loaded, including a heavy towed once you get slowed down on a long grade it's hard to get back up to speed.

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Old 09-09-2011, 06:19 AM   #3
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Jim, I am not sure what route you took but we just got back from a trip to NY that brought us home through Virginia and West Virginia on I-81 to Pigeon Forge, TN. From there we headed to Knoxville TN and picked up I-75 toward Chattanooga, TN.

We have a 40' DP with a Cat 330. We tow a 2004 Buick Rendezvous that weighs in at 4,200 lbs. In most cases, I let the Cruise Control manage the throttle and the gears while going up grades. I manually controlled the descending grades.

I think the lowest speed we got down to was 50 mph going up the longer grades.
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Old 09-09-2011, 06:25 AM   #4
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I would consider 25 mph on a 9% grade to be acceptable. We were down to 25-28 mph on 7% grades in the Rockies in our gasser with a 4000 lb toad, but we were still passing 18-wheelers. It's unfortunate for drivers behind you there was no passing lane or turnout, but is is what it is.
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Old 09-09-2011, 07:29 AM   #5
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Jim, I agree with bbeane. You have to keep up the momentum with a diesel, 9 times out of 10 that means you should force the transmission to down shift. The transmissions are set up to give you the best fuel mileage. They should have a 'Hill Climb' as the pickups have "Tow Haul".
If you know you are going to be getting into a hill force the transmission to down shift to keep the engine in the power band. Different engines are different but it is usually around 2-3 k for rpm.
I did not see where you said the weight of your unit but you know how it accelerates, you have to use the momentum of the unit and engine to get you up the hill.
It will not get you to 70 but you should pick up some speed and keep everything cooler.
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Old 09-09-2011, 08:12 AM   #6
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The best you can do is to maximize your torque when climbing steep grades. Follow this link and find your engine.


The info you want is the maximum torque rating and the RPMS where that occurs. Downshift your transmission, and adjust the throttle, to keep the RPMS as close to that number as you can. Note that maximum HP occurs at at higher RPMS but that is not what gets you up and over the mountain. Whatever speed you are going at while at the maximum torque output is the best that can be done.

When going down the other side keep your transmission in the lowest gear it took to climb up and over and keep it from upshifting by stabbing the brakes. Use your Pacbrake as well, assuming you have one.
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Old 09-09-2011, 09:07 AM   #7
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You didn't mention the weight of the combined coach & toad, but 350 hp is probably going to struggle on a 9% grade in any case. I have 370 hp ISL and tow an Acadia for a combined weight of 37,600 lbs. I do about 40 on a long 6% grade and would probably be at 30 on a long 9%.

To make sure you are getting peak performance, change the fuel filter and air filter. Even a small obstruction in either one can hurt peak power.
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Old 09-09-2011, 09:37 AM   #8
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First, I would avoid any 9% grades especially if I'm towing and extra especially if there's only one lane each way. If you're touristing park the coach and use the tow'd. If not, find an alternate. That's a pretty stiff grade for any motor / transmission / cooling system specially when you consider they're all stuffed into that "closet" in the back? We've done a couple of really short ones but only because we had to in order to get to that "special" CG or something. Failing that you want whatever gear keeps you at 2000 RPM or higher or you will have an overheating issue on a grade like that. I think 350 hp / approx. 1000 lbs. torque is being asked to work close to extreme on a grade like that with that much weight?
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Old 09-09-2011, 10:02 AM   #9
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I just leave mine to do it's thing. Pedal to the metal, let the computer manage the fuel. Trans in D, let the allison manage the gear.

Tach stays at 2200, downshifts come when needed automatically.

Yes, she will slow down on a tough grade, and 9% is tough as it gets.

Whatever u do, do not lift, keep her floored. U lift u'll lose boost, and then ur done, will never get the momentum back.
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Old 09-09-2011, 03:17 PM   #10
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Ya 9% you lucky your did 25. Even with out a toad that's tough pull.

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Old 09-09-2011, 05:10 PM   #11
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I thank all for the good advice. I think the one I like the best is to avoid 9 % grades. I'm knew to the motorhome world and probably bit off more than I can chew without more experience behind me.
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Old 09-09-2011, 06:25 PM   #12
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From cherokee to gatlinburg I down shift to a 3 speed pulling a ford expedition which weights a little more and I am able to push traffic up the mountain without a problem. What generally happens some dummy thinks that I will hold them up and pull in front of me, then they can read revolution in their mirror they rest of the way.
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Old 09-10-2011, 07:04 AM   #13
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I learned my lesson about being a "nice guy" by pulling over and letting cars pass. I pulled off in a gravel parking lot and my duals sunk to the frame.

No more mister nice guy.
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Old 09-12-2011, 07:48 PM   #14
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Yea let them lookat your grill or generator drawer the rest of the way up! Maybe give em acouple toots on the old air horn!

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