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There was an interesting topic on another forum discussing a new owners complaint that his ISL 400 Cummins lacked power when climbing steep grades. Not being a member I didn't comment. However, I was surprised at the number of people who recommended that he approach grades at full rpm with pedal to the metal and keep it that way during the entire climb. Perhaps gaining a minute or two in the process. Not to mention consuming fuel like he had a hole in his tank. My comment would have been that making a habit of operating a diesel engine in that manner would be the best diagnostic tool available if one was intent on eventually discovering a hidden, potentially  catastrophic, weakness in an engine or transmission. A flaw which otherwise might have remained unknown for the life of the coach.

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10 minutes ago, Gary Cole said:

There was an interesting topic on another forum discussing a new owners complaint that his ISL 400 Cummins lacked power when climbing steep grades. Not being a member I didn't comment. However, I was surprised at the number of people who recommended that he approach grades at full rpm with pedal to the metal and keep it that way during the entire climb. Perhaps gaining a minute or two in the process. Not to mention consuming fuel like he had a hole in his tank. My comment would have been that making a habit of operating a diesel engine in that manner would be the best diagnostic tool available if one was intent on eventually discovering a hidden, potentially  catastrophic, weakness in an engine or transmission. A flaw which otherwise might have remained unknown for the life of the coach.

Your correct.

These are not car's 

Many diesel techs never recommended full throttle operation.

I have never used a full throttle position. 

With any diesel 

Tractor trailer rig or our rv.

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Wow, that’s silly. How about just going down a gear, and maintaining speed with a few more revs. Amazingly that’s what Allison tranny recommend. 
isn’t that what gears are for? What am I missing? 
 

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I guess you guys must travel a lot in Florida where the highest elevation is maybe 350 feet above sea-level.

I have climbed many mountains both east and west of the Rockies, Canadian Rockies, all through Alberta, British Columbia, Yukon and Alaska and there have been many times that to keep the engine revving at about 2000 rpm's it requires that the fuel treadle be completely at the maximum. This has been while hauling a 30 foot 11,000 lb cargo trailer too.

There is one mountain that we climbed in Jasper National Park on the Ice Fields Parkway on our way to the Columbia Ice Field where I was at full throttle climbing at 12 mph in first gear for over 3 minutes. I defy any one with an ISB or ISC to not climb that mountain towing anything without having your pedal to the floor.

For those exact road conditions is why I highly recommend having an Exhaust Temperature Gauge (EGT) to monitor the temp making sure that it stays below 1250F.

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Some information posted here at times is. wives tales. Diesel engines are designed to be used. If anyone has set at a construction site and watched they would see lots of equipment runs wide open all day long, big generators or water pumps may run that way for months at a time. When a 250000 generator runs that way it is hard to believe running wide open hurts them. Farm equipment is used the same way. Ask a good diesel mechanic what is the hardest thing on a diesel engine. If he really knows he will say idling for long periods of time. Have been heavy equipment mechanic for 40 years so have a little knowledge about diesels

 

 

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2 hours ago, John Haggard said:

Your correct.

These are not car's 

Many diesel techs never recommended full throttle operation.

I have never used a full throttle position. 

With any diesel 

Tractor trailer rig or our rv.

I certainly do shift down manually on steep hills. 

Like the one north of Chattanooga on 111

North of sody daisy

Pulling my trailer with a jeep and harley behind.

The 500 hp ISM says cool and collected on the 15 minute climb North bound.

Running at 22 hundred rpm.

Even when shifted down to first at 3/4th throttle 

You don't go any faster at full throttle, I  assure you.

 

We pull that mountain range both ways 2 times a year. South of Cookeville Tennessee. 

I have family south of Denver.

Breakfast at Salida, then 

We ski monarch a few days then go on over to Crested Bute. 

So we have done the pulls. 

 

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Posted (edited)

I wasn't suggesting that our engines were not capable of full throttle operation. I routinely use full throttle when passing or climbing a short grade when I feel that more power would prevent a downshift. Transmission downshifts are not entirely free of wear and tear. Many years ago I was contemplating the purchase of a new truck with a Detroit 8V 92 engine. Detroit provided a spreadsheet which showed that the engine, when set at full rated horsepower, had a 40% shorter mean time between overhauls than when the engine was set at its lowest factory horsepower and rpm setting. In those days overhauls typically meant mean time between catastrophic failures such as broken crankshafts, dropped valves, piston separation, broken rods sticking through blocks, etc. Diesel engines have come a long way since then. 

I agree with Richard that a pyrometer is a good indicator of engine load and added one to my rv. I also use an engine oil temperature gauge as it indicates the real long term operating temp of the engine and whether it is tracking up or down. 

Edited by Gary Cole
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Lugging a turbo Diesel engine is harder on it than keeping the rpms close to the max. Exhaust gas temps will be higher and your cooling will be less at lower rpms. 
Only in the RV world is babying a Diesel engine the thing to do. 

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Hi RPM's doesn't nessesarily mean full throttle.

I have a 400 ISL, and climb many mountain grades in 3rd gear, 2000 rpm's, and boost pressure about 25in.

If I shifted to 4th, my rpm's would be in the 1500 range, but my boost pressure may be up around 33in.

So, which gear is easier on the drivetrain, and burning less fuel.

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Posted (edited)

Going up the mountain, down shift to whatever gear is needed to keep your diesel engine running at the best RPM for power which should be in the range of 1800-2500 RPM's depending on your engine. That will give you the best power band. There have been only a few grades I have traveled where I've been all the way down to first gear to keep the rpm's at peak power. However most only require going down to 3rd or 4th gear.

I keep my Cummins ISC-350 right around 2000 rpm's regardless of what the boost pressure gauge displays. The tach is your friend and what you need to monitor not the boost pressure.

Edited by Dr4Film
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2 hours ago, Dr4Film said:

Going up the mountain, down shift to whatever gear is needed to keep your diesel engine running at the best RPM for power which should be in the range of 1800-2500 RPM's depending on your engine. That will give you the best power band. There have been only a few grades I have traveled where I've been all the way down to first gear to keep the rpm's at peak power. However most only require going down to 3rd or 4th gear.

I keep my Cummins ISC-350 right around 2000 rpm's regardless of what the boost pressure gauge displays. The tach is your friend and what you need to monitor not the boost pressure.

This is something that confuses me. Doesn't the Allison take care of that? I've got a paddle shifter on my 2018 Ram 6.7 cummins/aisin dually but I've never used it. I've read lots of people on ram forums talk about how useful it is. My biggest climb has been Monteagle loaded with 16,500 lb fifth wheel and I just let the tranny shift itself.

I know the Monaco weighs a lot more, also mine has a lot larger engine, so maybe not apples to apples but it would seem the allison would be designed to keep it in the acceptable rpm range.

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3 hours ago, Dr4Film said:

Going up the mountain, down shift to whatever gear is needed to keep your diesel engine running at the best RPM for power which should be in the range of 1800-2500 RPM's depending on your engine. That will give you the best power band. There have been only a few grades I have traveled where I've been all the way down to first gear to keep the rpm's at peak power. However most only require going down to 3rd or 4th gear.

I keep my Cummins ISC-350 right around 2000 rpm's regardless of what the boost pressure gauge displays. The tach is your friend and what you need to monitor not the boost pressure.

The reason I mentioned the turbo boost pressure is to show that higher RPM's doesn't necessarily equate to higher fuel consumption. 

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21 hours ago, FishAR said:

This is something that confuses me. Doesn't the Allison take care of that?

I know the Monaco weighs a lot more, also mine has a lot larger engine, so maybe not apples to apples but it would seem the Allison would be designed to keep it in the acceptable rpm range.

If traveling on flat terrain the Allison will shift at approximate speed points not necessarily rpm's. After climbing and descending hundreds of grades I have learned important speed and rpm points on MY Allison and ISC-350 combination.

When climbing a steep grade the rpms's and your speed will degrade quickly. If you don't keep the rpm's in the 2000 range you are lugging the engine with not enough power. My Allison is always late to the party and such will drop to 1500 quickly whereas the speed may still be within the range that the Allison still likes therefore will not downshift to raise the rpm's for more power. I manually downshift once I see the rpm's starting to drop below 1800 with a lot more grade ahead.

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Posted (edited)

A Dynasty with a ISL-3000 Alison has a 4.78 axle ratio while the rigs with a 4000 Alison have a 4.33 ratio. When climbing with a ISL I’d keep the rpm above 1800 and now with a ISX it’s 1650 which equals 65mph in 6th on the flat.

Agree a fuel leak ^^^ after working on the turbo doesn’t add up…not sure the two were related. If I’d worked on your turbo I wouldn’t pay for a fuel leak.

Edited by Ivylog
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I’ve been following this thread with interest.  I have a 2012 Diplomat with the Maxxforce 10.  The torque is rated at 1250 lbs/ft at 1300 RPM and 405 HP at 2000 RPM.  I’ve driven primarily on the east coast.  The biggest mountains/hills here are nothing like those out west.  The biggest one near me is Afton Mountain on 64 near Charlottesville, VA.  There are some decent mountains in Pennsylvania while going to NY.

Should I be driving for max HP or max torque?
 

Dan D

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17 minutes ago, dandick66 said:

I’ve been following this thread with interest.  I have a 2012 Diplomat with the Maxxforce 10.  The torque is rated at 1250 lbs/ft at 1300 RPM and 405 HP at 2000 RPM.  I’ve driven primarily on the east coast.  The biggest mountains/hills here are nothing like those out west.  The biggest one near me is Afton Mountain on 64 near Charlottesville, VA.  There are some decent mountains in Pennsylvania while going to NY.

Should I be driving for max HP or max torque?
 

Dan D

Good question 🤔

Personally 

I climb mountains watching 

RPMs

Boost

Engine temperature 

Transmission Temperature 

 

We have never blown an engine on and RV or semi truck fleet.

In 50 plus year's. 

We train the drivers to keep the RPMs Higher the steeper the grade.

My 500 hp Cummins governor is set at 22 hundred rpm.

And only one mountain in Tennessee on 111  requires that in first gear with a trailer.

 

In Colorado 2,000 maybe 2,100 for a little bit.

But never shifted below 2nd climbing Monarch or Loveland pass. 

No trailer.

Just a 4 door jeep in tow. 

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Sometimes when I leave it up to the auto transmission. it can't make up its mind.  It will shift down then back up and may do that repeatedly.

That can't be good for it and it runs me crazy.  So that's one reason I will down shift even though the coach will make it up the hill with out me down shifting.

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3 minutes ago, Ray Davis said:

Sometimes when I leave it up to the auto transmission. it can't make up its mind.  It will shift down then back up and may do that repeatedly.

That can't be good for it and it runs me crazy.  So that's one reason I will down shift even though the coach will make it up the hill with out me down shifting.

Did you try efficiency mode 🤔

On gently rolling hills I like.. 

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"Sometimes when I leave it up to the auto transmission. it can't make up its mind.  It will shift down then back up and may do that repeatedly."------You are putting a lot of stress on the transmission by unlocking and then locking up the torque converter.  Chuck B 2004 Windsor

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1 hour ago, dandick66 said:

I’ve been following this thread with interest.  I have a 2012 Diplomat with the Maxxforce 10.  The torque is rated at 1250 lbs/ft at 1300 RPM and 405 HP at 2000 RPM.  I’ve driven primarily on the east coast.  The biggest mountains/hills here are nothing like those out west.  The biggest one near me is Afton Mountain on 64 near Charlottesville, VA.  There are some decent mountains in Pennsylvania while going to NY.

Should I be driving for max HP or max torque?

Dan, when climbing a grade use HP/RPM's. Remember, power is your friend not torque.

47 minutes ago, Ray Davis said:

Sometimes when I leave it up to the auto transmission. it can't make up its mind.  It will shift down then back up and may do that repeatedly.

That can't be good for it and it runs me crazy.  So that's one reason I will down shift even though the coach will make it up the hill with out me down shifting.

When my Allison starts hunting on rolling to moderate grades I always downshift to a gear that it will stay at. It's easier on the transmission.

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24 minutes ago, Dr4Film said:

When my Allison starts hunting on rolling to moderate grades I always downshift to a gear that it will stay at. It's easier on the transmission.

That's what I was trying to say,  thanks for clearing it up.     LOL

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2 hours ago, Chuck B said:

"Sometimes when I leave it up to the auto transmission. it can't make up its mind.  It will shift down then back up and may do that repeatedly."------You are putting a lot of stress on the transmission by unlocking and then locking up the torque converter.  Chuck B 2004 Windsor

Not to mention heat in the tranny fluid!

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