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Old 10-16-2018, 11:29 PM   #1
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Uphill trek

We have a 43’ 2010 Allegro Bus. It has an ISL9 Cummins 450hp motor and 6 speed Allison automatic tranny. We tow a Jeep Grand Cherokee.

We overheated once going up a 25% grade while towing the Jeep. Since then I had the radiator flushed and new fluid put in. I have a new air filter and radiator coils flushed.

We’re on a trip out west and I’ve noticed our rig will still approach overheating on long steep grades. It’s not quite gotten into the red but it was close. The transmission stayed in 5th gear and rpms stayed below 2k

We’re about to run I17 from Phoenix to flagstaff, AZ. It’s about 80 miles and 6000’ rise. I’m looking for advice on making the run and not overheat Should I unhook the toad and have the wife drive separate ?

Appreciate any guidance provided
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Old 10-17-2018, 01:45 AM   #2
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Quote:
Originally Posted by glsponchos View Post
We have a 43’ 2010 Allegro Bus. It has an ISL9 Cummins 450hp motor and 6 speed Allison automatic tranny. We tow a Jeep Grand Cherokee.

We overheated once going up a 25% grade while towing the Jeep. Since then I had the radiator flushed and new fluid put in. I have a new air filter and radiator coils flushed.

We’re on a trip out west and I’ve noticed our rig will still approach overheating on long steep grades. It’s not quite gotten into the red but it was close. The transmission stayed in 5th gear and rpms stayed below 2k

We’re about to run I17 from Phoenix to flagstaff, AZ. It’s about 80 miles and 6000’ rise. I’m looking for advice on making the run and not overheat Should I unhook the toad and have the wife drive separate ?

Appreciate any guidance provided
Is fan RPM tied to engine speed? If so you could try downshifting to a lower gear which would increase engine RPM and move more air through the radiator.
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Old 10-17-2018, 02:04 AM   #3
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It would be a good idea to disconnect and transfer any weight you can to the toad as a workaround. We just came down from Flagstaff last week where we got some overnight snow, and temps are even colder this week which should help as well, and of course take your time making the climb.
For reference, the 400hp ISL rear radiator in our 40' Newmar Ventana barely registered above normal temperature on the climb to Flagstaff, so you'll obviously want to get your cooling system further checked out ASAP.
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Old 10-17-2018, 04:13 AM   #4
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Shift it to 4th and see what happens.

25% grade ?
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Old 10-17-2018, 06:08 AM   #5
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overheat

Quote:
Originally Posted by glsponchos View Post
We have a 43’ 2010 Allegro Bus. It has an ISL9 Cummins 450hp motor and 6 speed Allison automatic tranny. We tow a Jeep Grand Cherokee.

We overheated once going up a 25% grade while towing the Jeep. Since then I had the radiator flushed and new fluid put in. I have a new air filter and radiator coils flushed.

We’re on a trip out west and I’ve noticed our rig will still approach overheating on long steep grades. It’s not quite gotten into the red but it was close. The transmission stayed in 5th gear and rpms stayed below 2k

We’re about to run I17 from Phoenix to flagstaff, AZ. It’s about 80 miles and 6000’ rise. I’m looking for advice on making the run and not overheat Should I unhook the toad and have the wife drive separate ?

Appreciate any guidance provided

Get your RPMs up , it should run cooler
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Old 10-17-2018, 06:17 AM   #6
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Downshift to 4th and slow down. On especially long steep grades I sometimes have to use 3rd
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Old 10-17-2018, 06:33 AM   #7
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Five million miles behind the wheel of a diesel(yes I'm one of those damn truck drivers), if it starts to get hot down shift and back off the throttle. The lower gear will allow you to ease off the throttle and maintain 2000 rpm. You may loose 5 mph, but your diesel will thank you.
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Old 10-17-2018, 08:13 AM   #8
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I had all my stacked radiators seperated, cleaned, reassembled, and the sending units (sensors) replaced. I have found the downshifting to solve many of my too hot issues. I also go a Silver Leaf System and found that my "too hot" problems were analog gauges that were off 10-15 degrees. What I want to know is where did you find a 25% grade hill? The steepest I've seen is 10% but that was only for less than a mile.
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Old 10-17-2018, 08:20 AM   #9
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Quote:
Originally Posted by Sonic View Post
It would be a good idea to disconnect and transfer any weight you can to the toad as a workaround. We just came down from Flagstaff last week where we got some overnight snow, and temps are even colder this week which should help as well, and of course take your time making the climb.

For reference, the 400hp ISL rear radiator in our 40' Newmar Ventana barely registered above normal temperature on the climb to Flagstaff, so you'll obviously want to get your cooling system further checked out ASAP.


Was that with your toad connected and no gear over rides ?
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Old 10-17-2018, 08:22 AM   #10
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Originally Posted by pumper9x9 View Post
I had all my stacked radiators seperated, cleaned, reassembled, and the sending units (sensors) replaced. I have found the downshifting to solve many of my too hot issues. I also go a Silver Leaf System and found that my "too hot" problems were analog gauges that were off 10-15 degrees. What I want to know is where did you find a 25% grade hill? The steepest I've seen is 10% but that was only for less than a mile.


The 25% grade was at amicola falls on GA. Beautiful place. I was very new driver at time and never thought a thing about the coach not wanting to make the climb
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Old 10-17-2018, 09:49 AM   #11
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As mentioned, keep the RPMs above 2,000 by downshifting. Also, your radiator fan should have two speeds. When the temperatures reach around 210, you should hear the fan go into high speed mode and the temps drop. If it's not doing that, then you may have a bad fan controller.
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Old 10-17-2018, 10:30 AM   #12
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Was that with your toad connected and no gear over rides ?
Yes, Honda CRV connected and no gear overrides
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Old 10-17-2018, 10:47 AM   #13
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I'm skeptical about the need for downshifting on a modern turbo-diesel engine in a motorhome. In most recent diesel-pusher chassis the fan is computer controlled and not really rpm dependent. Downshifting may help, but it shouldn't be necessary. I think you have something wrong with your cooling system, perhaps with the fan control or maybe some crap embedded between the layers of the radiator/CAC/AC_condensor.


Amicola has about a mile of 25% and averages more like 13% over the two+ mile length. Steep, but ought not to be a severe problem for the coach cooling system. Your engine can run comfortably at 210 over short distances like that, and the tranny should stay at or below 200 as well. Even 205 is ok for short periods.


I don't know if your Bus has the tiffin chassis or Freightliner and I'm not sure what Tiffin did for a cooling system on it. If Freightliner, it is definitely a multi-speed fan controlled by the ECM. Also, is it side radiator or rear? Some of the Allegro Buses used a rear radiator with the ISL and [in my opinion] they are marginal on cooling capacity.




I would not expect it to got hot at all on that gradual 80 mile clim.
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Old 10-18-2018, 09:22 AM   #14
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I would only do a 25% climb on an ATV. But the drive from Phoenix to Flagstaff won't give you anything steeper than 6-7%. It will be cold in Flag though.
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