We are thinking of getting a new diesel motorhome for more extensive traveling, but have a real problem. My criteria was an 400 ISL, but wife fell in love with a motorhome with Cat C7. I scratched Cat because of numerous problems I have read about, ie poor performance, smoking, numerous reflashes to get it to run right, lousy fuel mileage, etc. Have talked to several C7 owners who get 6 to 7 mpg--my gasser gets better than that with a total weight with towed of 26000#, not much less than the diesel. The old mechanical Cat's got 9 to 10 mpg with same engine. I am trying to keep peace in the family. Has the newer C7's overcome any of the problems mentioned above? Thanks for the input. Your replies will likely influence my decision.
2007 Allegro Bus QSP
06 Volkswagen Jetta Diesel
I've got 7800 miles on my C7, and I am perfectly happy with it. No smoking, lack of power or any of the other problems you have mentioned. I purchased my motor home in Nov. 2004, so I don't think it's one of the "newer" ones.
I tow a Saturn Vue occasionally, and it handles that just fine.
Go to Yahoo.com and search for the "CATRVCLUB" in the "groups" section. You'll find a wealth of information. I currently own a C7 330HP. To new to give you an information other than what I read at Yahoo.
I doubt that you'd have any real differences over the long haul with either engine.
We went with the ISL only because it came with 2-stage comrpession braking vs the engine brake that was available on the CAT. That was important to us because we do a LOT of mountain driving. Otherwise, would have gone with the CAT as it would have saved some big $$$ up-front.
I don't think you should compare the CAT 350 C7 and the Cummins 400 ISL. The 400 ISL would compare to the CAT C9. The C7 is a medium duty engine and the 400 ISL and CAT C9 are heavy duty engines.
I have read about the problems you describe regarding the C9, but not the C7.
This is my second coach with the C7. My first one, in an Itasca Meridian 35', started out at 7 mpg, but I averaged 8.5 after about 15,000 miles. I suspect it would have gotten better with more mileage.
My current coach is a Tiffin Phaeton 40'. After 9300 miles I have averaged 7.6 mpg. I expect it to improve with more miles as well.
I don't let the engine influence my motorhome choice too much, but given a choice on medium duty engines, I would pick the C7. For heavy duty engines, I would pick the ISL.
Apples and oranges! I "DID" let engine BRAND influence my purchase..because I was positive that Detroit was a NO WAY for me engine...and everything back in 2000-2001 that had a Cat installed was a 300-330 C7 or older series and didnt have the torque I wanted.
Now..when I made my purchase..IF..the 400 HP C9 Cat was available in rigs I wanted...might easily been a different story altogether. But even today if I had the choise..Id go with Cummins ISL with 2 stage Jake brake.
2002 Jeep Liberty
2016 Ford Escape
JoeT hit the nail right on the head. You can't compare a C-7 350 horse power engine with the bigger ISL 400 horsepower Cummins. If you want to compare: compare the C9 or C11 with the Cummins 400 ISL. Then you can say: I will go with the Big Cat. Better engine and better warranty on the Cat. 100K for the Cummins vs 500K for the Cat. The problems the C-7 had when in transition from the 3126-E have been solved with the reflashing and fuel mapping. Most C-7 owners I have talked to are very satisfied with the C-7.
I have driven both. the CatC7 was on a 2005 39ft Excursion, and the ISL400 in an Allegro Bus. The Ex drove fine up my "test grade" it actually felt like it pulled out faster than The ISL from a stop.I beleive wieghts were comparable because the Ex was fully loaded, and the Bus was empty. The ISL does have better passing power,more top speed than you need, and is much quieter . I also assume that there will be a noticable difference when towing, heck that 350LB of additional torque has to come into play somewhere.
Henry, Karin and the kids
2005 Allegro Bus 40 TSP Triple slide Cummins ISL400, all the goodies!
Jeep Wrangler toad,
2011 Alpine 3500RE
2001 Chevy 8.1L , allison, dually tow vehicle
I have 39ft Excursion, 2006 on Spartan chassis. Pull Yukon XL. No problems through mountains. Only about 10,000 miles so far, fuel mileage 7.5-8.0 on flat. First MH so hard to compare but seems to do just fine for us. Won't win any races but we are just into finishing.
Many times when the engine gets bigger the coach gets heavier, so a 40-footer with a 350hp C7 will offer performance comparable to, sometimes slightly less than, or sometimes slightly better than a 40-footer with a 400hp ISL. This is why a guy in a 37-footer with a 300hp ISB can pass a 39-footer with a 400hp ISL on a hill- one weighs 23,000 lbs. the other may weigh double that. Just depends on how each rig is outfitted.
Given a choice I'll always pick Caterpillar engines, only because of my personal experience with the brand. Mine runs smooth, pulls like a locomotive, and with only 5000 miles on it it gets 7-8 mpg. But if we found a rig we really liked with a Cummins, then we'd drive a Cummins.
Most people I know with C7's and ISL's get about the same mileage. If mileage is a big thing for you then you could always look at an ISB-powered rig- then you might see some measurable mpg difference.
As for engine reliability and owner satisfaction, neither engine has a history (that I'm aware of) of being problematic and I've never met anyone who was overly dissatisfied with either. You can always search these forums and look for problems associated with each engine but I think you'll find there won't be much to read on either.
IMO you should drive both then choose on floorplan and chassis handling...