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Old 01-03-2019, 06:04 AM   #1
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ISL vs X 15

Which engine is better, more reliable, trouble free - pros and cons.
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Old 01-03-2019, 07:16 AM   #2
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Big difference in size and probably the price of the RV's they come in. ISL has been around many years. X15 is a fairly recent replacement for the ISX.
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Old 01-03-2019, 09:11 PM   #3
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ISL vs X 15

Other than the fact that Cummins makes both engines, this is an “apples and oranges” kind of question.
The ISL is an 8.9 liter (540 cubic inch) engine with a max HP rating of 450 HP.
The X15 is a much larger 15 liter (910 cubic inch) engine with a max HP rating of 650.
They are two different engines that are used in different applications.
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Old 01-04-2019, 05:18 AM   #4
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You read about far fewer problems with the ISL than the ISX.
Also lower initial cost, lower maintenance cost, and better fuel economy.
But it love to put a ISX in where my ISL sits....
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Old 01-04-2019, 07:14 AM   #5
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Quote:
Originally Posted by Fiesta48 View Post
You read about far fewer problems with the ISL than the ISX.
Also lower initial cost, lower maintenance cost, and better fuel economy.
But it love to put a ISX in where my ISL sits....
The only part of this I'd disagree with is the fuel economy.

It took 15-20k miles for us to consistently see 7mpg with the ISL in our 2011 Revolution. Our current ISX equipped coach is about 5k lbs heavier but we've consistently gotten 7mpg starting with our very first tank of fuel. With favorable weather and terrain we can get close to 8 now (about 20k on the odometer)
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Old 01-04-2019, 01:40 PM   #6
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Jay We have found that too, we got 7.7 on the last fuel check with fill up. Our Essex with 500 ISM was maybe more in the 6.5 range with 140K miles and X15 is already at the 7 mile per gallon at 10K miles. London Aire with X15 weighs 8k more pounds then Essex with 500 ISM.
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Old 01-05-2019, 09:09 AM   #7
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No where have I read that 10k more lbs, 6 more liters, 1 more axle gets 8.8 mpg Iike my ISL9. Almost twice as many gal of oil and coolant on a ISX vs my 8.9 liter.
ISLs ARE CHEAPER TO BUY AND RUN. < That's a period.
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Old 01-07-2019, 05:16 PM   #8
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Some early ISL engines had a wrist pin issue. The serial numbers are posted above in this forum.
Some ISX 600 and 650hp engines have an intake valve failure issue due to acid corrsion on the intake valve from the Exhaust Gas Recirculation (EGR) system. So far, the X15 605HP owners are raving about them.

From other posts you made, did you mean to ask about the differences in the ISX12 and X15?
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Old 01-07-2019, 08:56 PM   #9
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Our 18 LA with the Spartan K3 chassis full loaded weighs 52,000 and towing a 5.5 ton 18 Durango which is a load. The ISL is a great engine but having 605 HP and 1950 torque out west in the mountains is a better choice.
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