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Old 06-12-2013, 06:20 PM   #15
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Just climbed the grade northbound I75 just south of Kentucky border. This was my first steep grade (not counting Florida hills.

I had the engine at 100% load going about 48 MPH with the transmission in auto (letting it select the gear).
Water temp got to 205F.
Should I have selected a lower gear manually and maybe not run at 100% load?
If it does get too hot I figure you pull over and let it cool.

I do use the selector for down grade and it works well keeping speeds and temperatures within range.

Thanks
I think you will find on the Allison that it probably won't downshift right away anyway. I can select a lower gear with mine and sometimes it stays right where it is. I think the only real way to shift with the selector is starting out manually shifting. That way it will stay in the lower gear longer as opposed to downshifting. I am only going up and down the Rockies, though. Not those huge mountains in KY. lol

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Old 06-12-2013, 06:46 PM   #16
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On our 2011 RED with the Allison Trans in the economy mode it will NOT allow you to select gears it has to be removed from the economy mode
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Old 06-12-2013, 07:00 PM   #17
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Was that just south of the TN-KY border north of Knoxville near Jelico?
Yes. I was not using cruise at the time just running 100% load on my 2001 Cummins ISC. . 205f was my max water temp and only happened once. I guess 220 would be the max (I presume the engine would derate then?). As the day progressed I did find manually finding 1900 RPMs seemed to keep the temps happy.
I used 5th or 4th downhill and followed the truckers.
Thanks for the info. Your experience is invaluable
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Old 06-12-2013, 08:50 PM   #18
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Was that just south of the TN-KY border north of Knoxville near Jelico?
Yes. After that I manually selected gears to run about 1900-2000 an the hottest I got was 194f. The grades didn't seem as steep as that one though.

Made me think I recently found I should have around 25 pounds of boost. I had about 5. Took it to cummins and replaced a cracked CAC. Probably would not have made the top under the old boost:(((. Imagine having to get towed up the hill.
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Old 06-12-2013, 09:00 PM   #19
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Here is what happened: When you exitied the tunnel with the cruise on you most likely running at about 50, the road flattens out enough for the trans to make one upsift putting in direct or 5th gear.
On the Allison 3000 and 4000 4th gear is 1:1 or direct, both 5th and 6th are overdrives.
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Old 06-12-2013, 09:07 PM   #20
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Originally Posted by dubdub07 View Post
I think you will find on the Allison that it probably won't downshift right away anyway. I can select a lower gear with mine and sometimes it stays right where it is. I think the only real way to shift with the selector is starting out manually shifting. That way it will stay in the lower gear longer as opposed to downshifting. I am only going up and down the Rockies, though. Not those huge mountains in KY. lol

WW
You will find that with the Allison you can only "preselect" a gear, the trans electronics will only allow a shift if it won't harm the engine or trans.
When using the exhaust or engine brake the trans panel will usually show "2". All that means is the trans will downshift as soon as possible to that gear. If the road is too steep the trans may shift up to protect the engine unless you use the service brakes.
You can select 1st on the panel, and accelerate and the trans will upshift no matter what you do.
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Old 06-12-2013, 09:20 PM   #21
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Sky_Boss is right. Keep RPMs up to keep engine and trans cool. Manually shift on long, steep grades, otherwise let the transmission manage itself.
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Old 06-12-2013, 10:33 PM   #22
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When climbing hills you want to keep your rpms up so you don't over heat.
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Old 06-13-2013, 06:18 PM   #23
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This entire thread isn't algebra to me, it's calculus! EEK. A mountain to me is what I drive by on I-95. A landfill. I'm dying to go west, but I don't want to die going west. Sometimes growing up in Florida is a bad thing . Mountain driving? Oh boy.
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Old 06-13-2013, 11:43 PM   #24
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The Allison 3000 is a great transmission, but I find if I wait for it to downshift automatically on a steep grade I find I'm already behind the curve. So, I manually downshift at 1500 RPM on the Cat 330 which is where I feel the torque becomes inadequate. I can easily downshift even in the economy mode and I try to find that happy medium of 1700-1900 RPM's which keeps the engine cool.
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Old 06-14-2013, 04:52 AM   #25
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It's not really rocket science

100% load is no problem until about 205degrees
So make that your max temp
Select a gear that will give you 2000 rpm on ISC 350.
No matter how steep it gets remember 2000 rpm and max 205
If temp goes beyond 205 drop a gear,lift the throttle to maintain 2000.
Just drop back gears to maintain these numbers and you won't go wrong.
I say 205 as a personal maximum as the pre emission engines ran a lot cooler than the latter model engines and 205 is quite hot enough for that engine.
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Old 06-14-2013, 06:01 AM   #26
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Agree.

I just climbed up from Golden CO to Breckenridge, CO. in my 2001 Diplomat 330 cummins. That is quite an experience for a guy from FL. on the way up I kept my RPM around 1900. My temp stayed around 205F. I am towing a jeep. At one point the incline got so steep my temp went to about 210F and I down shifted and slowed down. Keeping my 1900 RPM. temp wouldn't come down, so I pulled over for 5 minutes and got the motor temp down below 200F and completed the climb. At 9000 feet there is less air for cooling even though the outside air is cooler than lower altitudes. Keeping attention to the gauges really helps.


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This is the highest elevation pass in FL. This was my high altitude training.
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Old 06-14-2013, 06:59 AM   #27
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It's not really rocket science

100% load is no problem until about 205degrees
So make that your max temp
Select a gear that will give you 2000 rpm on ISC 350.
No matter how steep it gets remember 2000 rpm and max 205
If temp goes beyond 205 drop a gear,lift the throttle to maintain 2000.
Just drop back gears to maintain these numbers and you won't go wrong.
I say 205 as a personal maximum as the pre emission engines ran a lot cooler than the latter model engines and 205 is quite hot enough for that engine.
This is the technique to use.

In addition, I use 4 psi less than max available boost. My ISC makes 24 psi so I limit my foot to 20 psi.

The reason for this is as you go up in altitude the compressor must be spun faster to make the same boost. As it spins faster, after a certain point, it starts to heat the charge air more rapidly as it become less efficient. This added heat must be dealt with in the charge air cooler. It is similar to the drag rise you get from operating above 60mph, gradual at first but ramps up quickly.

I find that if the altitude is 5k or below it's hammer down. The grapevine, I75/77, etc., gives me 195F. Only when I get long grades at higher altitudes do I have to self derate.

FWIW
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Old 06-14-2013, 10:59 AM   #28
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Sky Boss is absolutely correct. You must anticipate your rpms and manage them before you get to the grade so that when you hit the grade you are able to have good power and lower temperatires. The one thing no one talks about is EGT (exhaust gas temperature) measured with a Pyrometer. I have an 8.3l "C" engine with a Banks kit and I drive it up the Grapevine watching EGT so that I am not exceeding the maximum exhaust temperature and possibly ruining my turbo or my engine as well as watching RPM and Temperature. I used to love having a 10speed or more transmission so that you could easily keep it in that "sweet" spot for maximum power and yet keep it cool. With only 6 speeds we are definately limited in what we can do.
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