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Old 08-06-2013, 09:01 PM   #1
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Dutch Star 4320 UpHill Questions

Our Coach has a 400hp ISL Cummins with low/high engine brake feature.

During our first trip this past week in Northern GA and South Western NC I noticed that RPM's don't rise past 1900-2000 when the pedal is to the floor. This is in automatic mode on our Allison 3200 6spd transmission.

Should RPM's be in the 23-2500 range?

What speed are most people maintaining while traveling up 3-7% grades?

TIA
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Old 08-06-2013, 09:33 PM   #2
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The Cummins ISL is governed at 2,200 RPM under power and 2,400 RPM when using the Jake Brake. So your RPM is right on the money.


However, you should not be climbing 7% grades with the tranny in Auto. Your coach is not a car...you cannot just put it in "D" and forget about it. You have to DRIVE it, and that means manually shifting down on the steep grades.

I cruise at 65 mph in our coach, which also has the 400 hp ISL engine. If I see a steep grade ahead, I will shift down to 5th gear as I hit the bottom of the grade and while still at 65mph. 5th gear at 65mph puts the RPM at 2,000...right on the HORSEPOWER peak for that engine. I can climb 6 and 7% grades at 65 mph in 5th with no problems.
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Old 08-06-2013, 09:38 PM   #3
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6-7% grades at 65mph is impressive. What is the weight of your coach, model, and length?
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Old 08-07-2013, 07:12 AM   #4
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In order to switch into manual mode while driving at say 65mph for example, all I need to do is press the down arrow once to downshift correct? Or do I need to hit the mode button? Also, if you are in auto and you downshift using the arrow button, will it then stay in manual mode?

Thanks
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Old 08-07-2013, 09:05 AM   #5
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Originally Posted by RHURRICANE View Post

In order to switch into manual mode while driving at say 65mph for example, all I need to do is press the down arrow once to downshift correct? Or do I need to hit the mode button? Also, if you are in auto and you downshift using the arrow button, will it then stay in manual mode?

Thanks
Correct. If you hit the down button, you are selecting 5th. If you hit it again, you will select 4th. It will continue to shift down as necessary but will not shift above the selected gear except to protect the engine in an over rev situation. When you wish to go back to auto just press the D pad. The mode is not a factor in this. The mode selects between two shift point schedules. Default is standard performance and when mode is lit the schedule is for economy.
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Old 08-07-2013, 10:11 AM   #6
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IMHO...don't spare the RPM on the climb.

I recently got my first chance to test out what we were taught at the Spartan factory when climbing Mount Eagle on I-24 in TN both east and west bound. Bottom line...attach the hill and be configured BEFORE you loose momentum.

As soon as I am about to hit the first big (relatively speaking for our west coast folks) I dropped to 5th and targeted 2000 RPM for the climb. Before I started these climbs my water temp was 199* and tranny fluid was about 204* and outside temps were in the 90s.

This put me at about 55 MPH and passing the trucks in the right climb lane without any problems. Here is the cool part...

As soon as I brought up the RPMs the water temp dropped 10* and within a few minutes the tranny fluid also dropped about 10*. On the east bound trip I got caught behind a truck that moved to the middle lane and then slowed us to 35 MPH. I didn't want to get in the left lane so I simply stayed with my strategy and down geared to 3rd and held 2000 RPM. When the truck move back to the right I had HP & torque to accelerate back up to 55 MPH and manually up shifted to 4th and then 5th as I hit a tad above 2100 RPM.

The reason for this is that the increasing the RPM increases water pump flow and fan speed. That is good.

On the big down hills I used the EB (only 1 stage in my 2006 model) and let the tranny do its job. I do not use cruise control as I talk about further down. on the WB downhill with the big sweeping right hand turn near the bottom you really need to get slowed down before that curve! I followed the 45 MPH truck speeds on the downhill portions. The tranny would automatically drop me down to 2nd and run up to about 2300 RPM and then recover properly as I added throttle.

BTW...when I am cruising at 62 MPH on rolling hills I use the EB with cruise control because it kicks the EB on automatically at 3 MPH above the cruise control setting. Since my CRV has a 65 MPH tow speed limit, that works just fine.

One other point that you alluded to for tranny controls. I do NOT use the economy setting when in moderate to heavy traffic on rolling hills because it causes too much of a delay in reacting to needing more throttle on the uphills which confuses folks behind me. This might cause the tranny to shift a bit more often but that is OK. OTOH, if it is a nice 4 lane without out much traffic I often go into economy mode to to minimize gear hunting.
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Old 08-07-2013, 10:20 AM   #7
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...

What speed are most people maintaining while traveling up 3-7% grades?

TIA
BTW...don't worry about speed. Sure, it is nice to pass the trucks in the slow lane because they can get VERY slow. Still, don't forget you have a heavy beast and you can't think like a car. That doesn't even take into consideration the car drivers thinking they are competing to reach the top like a racer. Respect your mass and avoid the stupidity of others and you will be safe.

So...on the uphill climbs if the trucks are limited to 55, I do 55 as long as my motor says it is happy. If it starts getting sad, I go slower and keep the RPM up. On the downhills if the trucks are limited to 45, I do 45. The thing I have noticed is that on climbs, yes, trucks will sometimes/often not be doing 45 but will be slower. OTOH, on the downhill side with a 45 MPH restriction the far right lane will be doing 45 MPH pretty consistently.
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Old 08-07-2013, 06:12 PM   #8
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6-7% grades at 65mph is impressive. What is the weight of your coach, model, and length?
Our coach is a 2006 Mandalay. 41' long and 34,000 pounds. 400 HP Cummins ISL
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Old 08-09-2013, 07:28 AM   #9
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Thank you all for your help!
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Old 08-09-2013, 10:29 AM   #10
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Quote:
However, you should not be climbing 7% grades with the tranny in Auto. Your coach is not a car...you cannot just put it in "D" and forget about it. You have to DRIVE it, and that means manually shifting down on the steep grades.
I have to disagree. My Allison 3000, in conjunction with the engine computer, keeps the RPMs right at the peak horsepower point when I leave it in Drive and push down the go-pedal to climb a grade. No need to downshift manually, and in fact downshift manually has no effect, since it is already doing the very best it can. Maybe manual shifting is of help on older coaches, but I doubt if you can improve on what the automatic does if the coach is newer than around year 2000.

And the built-in two-speed Jake brake on my ISL does the same going downhill. It targets 2nd gear and manages the actual gear according to the speed I choose.
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Old 08-09-2013, 04:11 PM   #11
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I have to disagree. My Allison 3000, in conjunction with the engine computer, keeps the RPMs right at the peak horsepower point when I leave it in Drive and push down the go-pedal to climb a grade. No need to downshift manually, and in fact downshift manually has no effect, since it is already doing the very best it can. Maybe manual shifting is of help on older coaches, but I doubt if you can improve on what the automatic does if the coach is newer than around year 2000.

And the built-in two-speed Jake brake on my ISL does the same going downhill. It targets 2nd gear and manages the actual gear according to the speed I choose.
Same here. Don't try to out smart the Allison...put it in D and let it do the driving. When going down hill use low or high on the engine brake, depending on how steep the hill is, and you'll never touch the service brakes.
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Old 08-09-2013, 04:40 PM   #12
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There are times when manually downshifting is necessary-- like when towing a 7000# boat up a 6-7% grade, and you're getting near overheating...

Last summer towing our Chaparral on vacation I had to stop a few times to avoid overheating... Fast forward to this July and thanks to many folks on this board I discovered my radiator was plugged due to the infamous slobber tube venting oil mist directly under the radiator. I figure I have it about 2/3 cleaned out good, still need to do a front-side degrease with the Simple Green.

Over the 4th we towed the boat up Daniels canyon which gets pretty steep. I found that simply pedal to the metal was fine until I started running out of power in 5th, then the temp started to climb. Got pretty close to the red and at around 1500 rpm it still didn't automatically downshift so I did it myself- and as Sky Boss noted above, IMMEDIATELY the extra rpms dropped the temps. I found myself manually downshifting to 3rd about a mile later, temps immediately dropped again. Made the rest of the hill just fine in 3rd.

It's probably because my radiator still needs some final cleaning, but the fact remains, had I not downshifted manually, I would've had to nearly stop to avoid overheating...
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Old 08-09-2013, 09:19 PM   #13
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I have to disagree. My Allison 3000, in conjunction with the engine computer, keeps the RPMs right at the peak horsepower point when I leave it in Drive and push down the go-pedal to climb a grade. No need to downshift manually, and in fact downshift manually has no effect, since it is already doing the very best it can. Maybe manual shifting is of help on older coaches, but I doubt if you can improve on what the automatic does if the coach is newer than around year 2000.

And the built-in two-speed Jake brake on my ISL does the same going downhill. It targets 2nd gear and manages the actual gear according to the speed I choose.
I do not know about your coach but my owners manual does not agree with you on my 2005 tiffin with the 400 isl engine. The freighliner manual says to downshift to keep my engine RPMs up to keep the engine from overheating. I have climbed grades and had my transmission in 6th gear and no problem with power but the engine started getting hot. I manually downshifted and the temp started dropping.
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Old 08-09-2013, 10:54 PM   #14
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Does any one watch their EGT temperatures when climbing hills. I do not have a Pyro gauge but thinking i should install one.
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