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Old 10-31-2019, 07:04 PM   #1
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Cummins ISL 450

Looking at upgrading to a newer coach 2017 Newmar with the Cummins ISL 450. Im a BIG CAT fan and would like to hear from people with the one in question Pros and Cons for this engine. Been over 30 years since I ran a Cummins, last one the 855 Big Cam 400.

First had knowledge is what I'm wanting to hear Please. The more the better.


Thanks for your information
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Old 10-31-2019, 08:39 PM   #2
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Old 10-31-2019, 09:04 PM   #3
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No complaints at all! The ISL9 coupled with the Allison is a great combination.

22,000+ miles on our 2017 450 and not as much as a wrong burp from the engine. I know I probably just jinxed myself.

Since it is that time of year... The one thing that surprised me coming from an older coach. Cummins says you don't need to use the engine block heater unless the temperature drops below 0F.

I've tried it a few times in single degrees, and it started easily. No smoke, or slow cranking. Just a longer intake manifold preheat cycle before the idiot lights give you the ok to crank.

We have a two stage engine brake. I have yet to find an interstate grade that I had to stab the brakes more than once on. Mostly the lowest stage holds speed, but occasionally I've used the higher stage kind of like stabbing of the brakes. Slow me down below my desired speed then back to lower level until I get 5-10 over, repeat. It isn't nearly as fast as full brakes, but it will usually slow you down below what you want to drive.

I would say probably driver error that I've ever had to use the service brakes.

Of course if you get into the 10%+ grades you will have to use the service brakes, but I haven't seen those on any interstates yet.

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Old 10-31-2019, 11:18 PM   #4
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We've got 47K over 5 years on the 450 - been up and down just about every mountain in the country with no problems with a gross combined weight of 45K w/full fuel/fresh water tanks. On the climbs over 6 - 7% we cruise at 2000 rpm and let the temp drive the speed - often in the 40s to 50s.

In the last 3 months in Wyoming, Utah, Colorado, New Mexico and Arizona we've been averaging 8.6 mpg maintaining a max speed of 63 mph.

Have addressed one check engine light - best guess is bad DEF - and we're currently chasing a short in the 2 - stage engine brake. Other than that we're very pleased.
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Old 11-01-2019, 12:15 PM   #5
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The ISl9 is the most efficient engine in the world regarding torque per pound of weight. It is large enough to get the job done and small enough you don't have to go up in tire size or loose cargo carrying capacity.

Some would argue, however for that size engine the best Cummins or anyone else has ever manufactured. That is why you see them in almost everything until you cross over the 1/2 million dollar mark and the larger engines start to show up.
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Old 11-02-2019, 12:56 PM   #6
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No complaints with my L9 Cummins except that during break in at a bit over 3K miles, I'm currently getting only 6 mpg (was only 5 out of the gate). Was in Colorado earlier this week and with temps in the teens, it started like it normally does at higher temps. Weighed loaded rig at 45K lbs and did the Raton Pass while heading south on 25 this week. While it's not a rocket, it handled it both up and down. I have a 3 stage engine brake.

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Old 11-03-2019, 08:19 PM   #7
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Cummins added a slightly longer stroke crankshaft to the 8.3L ISC and the 8.9L ISL was born. It's a great motor, but a ways from your current Cat C12 and a mile away from your old 855.
Look at the torque rating on your C12 and the torque on the ISL.
Then look at the weight on your Marquis and the weight on the 2017 Newmar. You are also stepping down from an Allison 4000 series to a 3000.
That will give you a feel for the new coach.
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Old 11-03-2019, 08:35 PM   #8
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Quote:
Originally Posted by 1doodadd View Post
Looking at upgrading to a newer coach 2017 Newmar with the Cummins ISL 450. Im a BIG CAT fan and would like to hear from people with the one in question Pros and Cons for this engine. Been over 30 years since I ran a Cummins, last one the 855 Big Cam 400.

First had knowledge is what I'm wanting to hear Please. The more the better.


Thanks for your information
You really don't have a brand choice in a motorhome for anything other than a Cummins... Unless you're shopping for a Prevost with a DD. The Cummins 450s and 605s seem to be highly reliable, the older 500s have had some significant mechanical issues.

Cat(and Mercedes) dropped out of the motorhome race many years ago when they chose not to meet EPA 2007 standards.
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Old 11-03-2019, 08:39 PM   #9
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You'll never notice the difference between the 3000 and 4000 MH trans.
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Old 11-04-2019, 02:53 PM   #10
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Originally Posted by Mr_D View Post
You'll never notice the difference between the 3000 and 4000 MH trans.
Yes and NO. Yes both are great transmissions that give very little trouble BUT a 3000 is limited to 1200-1250 ftlbs of torque. A 4000 can handle 1850+.
A ISL is a good engine and the torque is basically the same...400,425,450 HP are all the same torque. If using the 1HP/100 lbs of weight rule of thumb, use 400 HP for all the ISLs. I thought I was happy with a ISL 400 in a 42K lb coach until I got a Cummins 1650 ftlbs (525HP) ISX in a 45K coach...world of difference.
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Old 11-04-2019, 09:44 PM   #11
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Quote:
Originally Posted by vito.a View Post
Cummins added a slightly longer stroke crankshaft to the 8.3L ISC and the 8.9L ISL was born. It's a great motor, but a ways from your current Cat C12 and a mile away from your old 855.
Look at the torque rating on your C12 and the torque on the ISL.
Then look at the weight on your Marquis and the weight on the 2017 Newmar. You are also stepping down from an Allison 4000 series to a 3000.
That will give you a feel for the new coach.

According to my Silverleaf my torque is around 1650, and 450 hp, and not to mention I get right at 8 mpg. I believe I will keep what I have and not acquire and NEW payments at this time.

I would like to Thank ALL who have given their opinion and time in this matter
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Old 11-05-2019, 07:18 AM   #12
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Wise choice as you’re spoiled with that much torque. Next time you get the bug if the poor woodwork is not enough, go drive one with a ISL. Your 1650 out of a 12L engine is really good...I only get that out of a 15L engine but then your 2000 engine is not new and improved with all the emission stuff...another reason to keep what you have.
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