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Old 08-30-2014, 08:03 PM   #1
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Shift or Not to Shift

I just read an interesting question about best RPM to climb mountains. Trust transmission or shift on your own to keep best RPM power.
My question is this... I have a 2000 Dutch Star diesel pusher with Allison
6 sp. I'm planning a trip from middle Georgia to Ohio soon. The mountain from Knoxville TN over to the KY side is pretty steep. Should I do the shifting going up over the top or let the MH decide and do what it is programed to do? What RPM is best for my engine?
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Old 08-30-2014, 08:07 PM   #2
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Your manual should tell you the best cooling RPM and this would be the RPM for good power and torque. On my Cat that is 2200 RPM and I try to stay near that on the long climbs.

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Old 08-30-2014, 08:41 PM   #3
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I have been through that area a couple of times. I typically just let the computer do it's thing. I'd do pay attention to both engine and transmission temp. So far the Allison has done a good job of shifting when necessary. I also don't care if I do 45 up a steep grade. If needed I'll just get in line with the semi's and enjoy the scenery.
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Old 08-30-2014, 09:02 PM   #4
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On my CAT the 2000- 2200 rpm range is where I make the most power. I try to keep it in that range. If you rely on the tranny to downshift, by the time it recognizes the need to shift, and it shifts, you'll have lost 10 mph that you will not get it back on that grade. Just my way of doing it, and it keeps the temp down too.
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Old 08-30-2014, 09:06 PM   #5
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Pay attention to temperature and RPMs. If RPMs start to drop and the temperature is going up, downshift to ease engine lugging and increase coolant circulation. Often the best transmission computer will keep you in a higher gear than what's best for the conditions. Speed is the least important when climbing hills, Temperature and RPMs are the things to pay attention to.
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Old 08-30-2014, 09:16 PM   #6
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Ah yes, Mount Eagle on I-24. I have done that a lot. I have a Cummins 400 ISL so this may or may not apply to you. I am not a fan of letting the tranny do it for you. It works but I don't think I like giving control to it.

Going up Mount Eagle I move to the truck lane and before I hit the big grades down shift to hold about 2000 - 2050 RPM. When I do that it drops water temps about 10* before the climb and holds it between 190* & 200* during the climb. It gives me enough momentum that if I don't get blocked in by cars in the left lane and I get behind a really slow truck I can get around them and accelerate just a tad. If I get "stuck" well then I just sit back and enjoy the ride. LOL

Don't forget to set your engine/exhaust brake before the down hill side. Personally, just before you get there, set it. On the downhill side I let the tranny drop me down to 2nd gear and stay in the truck lane. If you get to 50 MPH...brake firmly down to 45 MPH, repeat as needed. You could even consider targeting 40 MPH and braking at 45 MPH. Remember, at least for the Cummins engine, you zero thrust red line is higher than your full throttle red line. You most effective engine brake horse power is at the top of the zero thrust red line.

Mount Eagle is nothing compared to west coast MOUNTAINS but it takes a disproportionate number of lives. I think the reason is that folks don't respect it. It is a good test for new folks and their braking skills if respected.

YMMV
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Old 08-30-2014, 09:37 PM   #7
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Quote:
Originally Posted by Sky_Boss View Post
Ah yes, Mount Eagle on I-24. I have done that a lot. I have a Cummins 400 ISL so this may or may not apply to you. I am not a fan of letting the tranny do it for you. It works but I don't think I like giving control to it.

Going up Mount Eagle I move to the truck lane and before I hit the big grades down shift to hold about 2000 - 2050 RPM. When I do that it drops water temps about 10* before the climb and holds it between 190* & 200* during the climb. It gives me enough momentum that if I don't get blocked in by cars in the left lane and I get behind a really slow truck I can get around them and accelerate just a tad. If I get "stuck" well then I just sit back and enjoy the ride. LOL

Don't forget to set your engine/exhaust brake before the down hill side. Personally, just before you get there, set it. On the downhill side I let the tranny drop me down to 2nd gear and stay in the truck lane. If you get to 50 MPH...brake firmly down to 45 MPH, repeat as needed. You could even consider targeting 40 MPH and braking at 45 MPH. Remember, at least for the Cummins engine, you zero thrust red line is higher than your full throttle red line. You most effective engine brake horse power is at the top of the zero thrust red line.

Mount Eagle is nothing compared to west coast MOUNTAINS but it takes a disproportionate number of lives. I think the reason is that folks don't respect it. It is a good test for new folks and their braking skills if respected.

YMMV
Between Knoxville and Kentucky, on I-75 is Jellico Mountain, I believe. I-24 goes from Chattanooga to Nashville, to Paducah. I-75 would be the route from mid Georgia to Ohio.
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Old 08-31-2014, 06:39 AM   #8
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We also have a 2000 Dutch Star, ours with a Cummins. When going up I always manually shift down on the longer steeper grades to keep RPM's between 1800-2000. Engine will run a lot cooler in those ranges. If you don't down shift she'll lug down and start getting hot.
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Old 08-31-2014, 06:57 AM   #9
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If going up the hill and transmission starts hunting between gears. It is best to manual shift.
If temperature rises above 205 then downshift to keep RPM 2000-2200.
Take transmission out of "MODE" when in hill area.

Going downhill the exhaust brake works best from 2000-2900.
Use brakes to slow RPM down when it hits 2900-3000 before the transmission will up-shift automatically.
You can manually downshift going down hill but it will up-shift anyway when it hits around 3200 RPM. At least my ISB with the MH3060 works that way.
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Old 08-31-2014, 09:38 AM   #10
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Two weeks ago we sat in on the Silverleaf seminar at the Fmca Rally in Redmond Oregon. Here is what I learned.

Max engine temp on a Cummins ISL is 226 for 5 min.

Turbo inlet temps are the first indicator of what the water temperature will be doing. As the turbo spins up and compress the air higher temps are created in the cylinders along with more fuel to handle the load.

Almost always use economy mode on the transmission.

If you have watch the turbo inlet temps you will learn how hot the water will get if you continue at that load. If you know from practice that the inlet temps will take the water temps too high slow down a mile an hour or to and watch the turbo inlet temps come into line.

Down shifting on a hard pull and an already high water temp can cause water temps to rise slightly. Remember that on a down shift you be raising the turbo spin rate because of the increase in rpm. This will increase the turbo inlet temps more. It would be best to learn what speed will allow you to keep the engine happy temp wise. Hot days may mean that you crime at 3 mph slower on a 6 % grade that day. Randy
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Old 08-31-2014, 09:49 AM   #11
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Quote:
Originally Posted by BFlinn181 View Post
Between Knoxville and Kentucky, on I-75 is Jellico Mountain, I believe. I-24 goes from Chattanooga to Nashville, to Paducah. I-75 would be the route from mid Georgia to Ohio.
YEP...you are correct. I missed that right turn. LOL I think the rest is still appropriate.
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Old 08-31-2014, 10:04 AM   #12
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Quote:
Originally Posted by fixit1957 View Post
Two weeks ago we sat in on the Silverleaf seminar at the Fmca Rally in Redmond Oregon. Here is what I learned.

Max engine temp on a Cummins ISL is 226 for 5 min.

Turbo inlet temps are the first indicator of what the water temperature will be doing.

...

Down shifting on a hard pull and an already high water temp can cause water temps to rise slightly. Remember that on a down shift you be raising the turbo spin rate because of the increase in rpm. This will increase the turbo inlet temps more. It would be best to learn what speed will allow you to keep the engine happy temp wise. Hot days may mean that you crime at 3 mph slower on a 6 % grade that day. Randy
A few counter points.

I REALLY wish I had a EGT/pyrometer. On my wish list. I'm not as familiar with turbo inlet temps and how that changes with turbo spin rates. What do you have/use to determine the inlet temp?

While I can see what you are saying about higher engine RPM means higher inlet temps, I think that depend on some cooling system configurations. In my case the higher engine RPM results in higher radiator fan speeds. As I approach a climb, if I down shift about 1/2 mile ahead of that climb (usually about the time you see truck speed signs anyway), in that 1/2 mile my water temps drops 10* - 15* before the real meat of the climb arrives.

I think EGT is probably a better measure of turbo work loads. Combined with turbo boost info I think one can have an accurate picture on what is going on.
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Old 08-31-2014, 10:17 AM   #13
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Higher rpm's mean higher water flow. The water can not be cooled without going through the radiator. All my customers who manually shifted down, had no heating problems. (of course that means if they had no engine or radiator problems.) The ones who lugged the engines complained of high temperatures.
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Old 08-31-2014, 10:33 AM   #14
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Why not try it in auto on the way there, manual on the way back? One way might be better. 😄
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