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Old 05-14-2012, 08:52 PM   #15
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All things being equal (an they usually never are) I'd take the CAT over the Cummins in those engines. Given a choice I'd rather have an ISC or ISL though.

2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft
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Old 05-14-2012, 08:54 PM   #16
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Originally Posted by JPMaly View Post
I owned a 99 HR Endeavor with the cummins 5.9 and now I own a 03 Jayco Avatar with the Cat 3126. The cummins got great fuel mileage, even when towing Honda Element. However, it lost all game trying to pull any slight grade. It also had the dreaded 53 block ( do a search ), so I did not feel comfortable adding a banks kit, though some do. The Jayco has 330 hp ( 55 more than the 275 cummins) and 840 lbs torque ( A plus 180 over the 5.9) I can pull the Cajon Pass, 55 mph at the weigh station and maintain 55 to the top of the hill. Avg 9 miles per gallon. I think the 02 is a 3126, slobber tube and most likely has a grease zirk on the fan pully, mine does. One could never have too much hp, but remember, more horses, more $hay$
Not necessarily, some of the ISL's will get better mileage than some of the 3126's or ISB's. The bigger engines are turning slower and if properly matched to the load and driven right they do get good mileage.

2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft
Charter Good Sam Lifetime Member, FMCA, SKP
RV'ing since 1957, NRA Benefactor Life, towing '05 Odyssey
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Old 05-14-2012, 11:31 PM   #17
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ISL getting better fuel mileage than a 5.9 or even the 3126, is rare. But then again, some owners always catch bigger fish.
My Avatar is my Avatar, 2003 Jayco 3800, that is.
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Old 05-26-2012, 07:32 PM   #18
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My last MH had a Cummins in it. Got 12 MPG towing a Jeep Wrangler, and had enough power to scramble over the Rockies as if they were ant hills. Just got a new MH with a Caterpillar c7. What a piece of garbage, no power, no torque, and 6 MPG. Just listen to them, the Cummins sounds like a diesel should sound, the Cat sounds like a gas engine trying to act up.
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Old 05-26-2012, 08:44 PM   #19
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There are thousands of both engine successfully powering trucks, motorhomes, etc. Both are very good. NEITHER is "better". As usual, you tend to get the same lame Ford V. Chevy arguments, with those owning each rabidly defending their mighty motor. Unlike most poster here, I've owned coaches with both engines. The major difference I noted, was the 5.9 is a small block, with very low torque output. The CAT, at 7.2 liters has substantially more torque, and that's where the difference lies. Torque is what gets you going, and climbs hills. While the Cummins 59. ran great in our prior coach, it had a mere 520 lb ft of torque. Our current CAT powered coach has 860 lb ft. Big difference.

For anyone to claim either is junk, or inferior as a reliable powerplant; is ridiculous & ignorant.
2012 Montana 3582RL
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Old 05-27-2012, 05:00 AM   #20
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We have the ISB 5.9 in a 28k, 40' DP. I was concerned about the small ISB and called Cummins to get their input. As always, the Cummins service/rep was outstanding and informed me that my engine was the last 5.9 off the floor in mid 2007. He said that was good because by then they had worked out all problems with the little engine. I then had the Banks Power system installed and was really impressed with increase in Hp but more impressed by new found torque. With a 4,000 lb Wrangler toad, we have no problem on any terrain. I normally leave power setting at 2 and engage Allison Economy push for the flats and disengage push and power set at 3 for any Georgia/Alabama I-20 rolling hills. If I need to keep up with truckers, I'll up power to the number 4 for awhile until flattening out. Number 4 will increase exhaust temp, but EGT hardly ever goes to 1200 and if so, doesn't stay there long. The Banks puts the power range of the 5.9 up to at least the 6.7 output. On a recent 2500 mile trip to Dallas, we averaged an accurate 8.6 mpg. The Banks system really works great. If your interested, there's a good write up of the Banks system in the March '12 issue of MotorHome.

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cat, cummins

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