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Old 01-13-2012, 08:50 AM   #15
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Hi AloraDanin,

As to torque, forget it. For motor coach applications, there is an almost automatic relationship between HP and torque. When you get more HP you get more torque.
Gary, I disagree. You can buy the same motorhome with a Cummins ISB 5.9L or the Cummins ISC 8.3L engine. They will both have the same 300-350 HP rating, but the torque rating on the ISB is 500-600 ft lbs vs the ISC is 900-1100 ft lbs. The Cummins ISC will have twice the torque of the Cummins ISB.

I am a big fan of the Cummins ISB and have one in my pickup. But there is a big difference between a 6000 pound vehicle and a 30,000 pound vehicle. The ISC will run cooler, tow better, and last longer in a motorhome application.
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Old 01-13-2012, 08:53 AM   #16
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Cat is no longer in the "over the road" engine business, especially for motorhomes. One wonders how much longer Dealers and even Cat shops will continue to stock parts for older, smaller engines and how difficult it may become to find good, reasonably priced service? As a rule, Cummins provides more torque per cubic inch than Cat and torque is what pushes a coach up a hill,period. Even if you're only driving some of the time an engine that is not "stressing" is much more likely to provide lots of miles of motoring without too many headaches?
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Old 01-13-2012, 09:10 AM   #17
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Cat is no longer in the "over the road" engine business, especially for motorhomes. One wonders how much longer Dealers and even Cat shops will continue to stock parts for older, smaller engines and how difficult it may become to find good, reasonably priced service? As a rule, Cummins provides more torque per cubic inch than Cat and torque is what pushes a coach up a hill,period. Even if you're only driving some of the time an engine that is not "stressing" is much more likely to provide lots of miles of motoring without too many headaches?
IMHO the hundred of thousands (millions?) of CAT engines installed in trucks throughout the country will keep the maintenance network available for much longer than the CAT-equipped MH's will remain on the road. There are plenty of MH's, buses, and trucks routinely getting service even though they have obsolete engines such as the Detroit Diesel 8V92. Trucks are simply not like cars, they don't get scrapped after a few years of use. Between truck service facilities and CAT service centers we have absolutely no problem getting service and I doubt I will live long enough for that to ever change. These are million mile engines; they will be around a lot longer than I will.

As for torque per cu in of displacement, I've never heard of truck engines described this way because it simply doesn't matter. These are not small engines in the first place and squeezing a bit more power out of a small engine is irrelevant. Cummins and CAT marketed engines that were matched in output across a broad performance range: the Cummins ISC competes against the CAT C-7, the ISL competes with the C-9, the ISM vs the C-12, and the ISX vs the C-15.
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Old 01-13-2012, 09:20 AM   #18
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Even two engines with the same torque rating can be vastly different. It depends on the torque curve more than the actual amount. Our ISC has 1200 Ft lbs from 1400 to 1700 rpm, which is a much wider spread than most, even the ISL 400/425 doesn't match that.
I'm not going to try to tell you what is in your MH, but 1200 ft-lbs of torque from an ISC is way beyond any specs I have ever seen for this engine. Here's a link to a table which provides common performance configurations for the series of Cummins on-highway engines. http://www.dwclutch.com/D&W/D&W%20Cl...S%20TORQUE.pdf

The ISC is an engine designed for the ~1000 ft lbs market, the ISL is ~1200 ft lbs, the ISM ~1500 ft lbs, the ISM ~1700 ft lbs.
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Old 01-13-2012, 09:22 AM   #19
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Sorry, I was over generalizing by using cubic inch comparison. You're right, the C7 compares with the ISC in the motorhome market anyway. The C7 is generally advertized at about 860-890 pounds of torque while the ISC is advertized as 1050 - more cubic inches in the ISC by the way. It is still my contention, and always will be, that it is torque that does the work, hp only gets you to your place of work! Unless something changes Caterpillar has made it clear that they are going to focus on marine, military, and off*road applications only ... it makes sense to consider this when choosing the engine that will power your coach? There will always be somebody to service a Cat engine I agree, but it may not be a place you particularly want to take your motorhome as well as your dump truck?
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Old 01-13-2012, 10:04 AM   #20
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Is bigger always better?

Barbara
IMO, Yes, Bigger is better.

It has been my experience and observation that small engine(ISB, C, L) MHs have overheating issues much more often than large engine(ISM, X, DD) MHs when doing long climbs in the summer time.

The tread in later models coaches is to make them fancier and heavier with smaller engines. IMO, that's a bad combination, and they don't get better fuel mileage. They are just under powered, ralatively speaking.

Don
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Old 01-13-2012, 12:13 PM   #21
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Cat is no longer in the "over the road" engine business, especially for motorhomes. One wonders how much longer Dealers and even Cat shops will continue to stock parts for older, smaller engines and how difficult it may become to find good, reasonably priced service? As a rule, Cummins provides more torque per cubic inch than Cat and torque is what pushes a coach up a hill,period. Even if you're only driving some of the time an engine that is not "stressing" is much more likely to provide lots of miles of motoring without too many headaches?
How difficult is it to find good, reasonably priced service today?

One can wonder how long you'll be able to get parts for a model T too. You can build a complete 57 chevy from aftermarket/nos parts. I wonder how long that will be available? I tried to get a windcup for my Careless of Colorado awning that is 3 years old and it's obsolete and unavailable from the factory. Guess we should never buy an RV with one of those either. Mercedes has stopped importing their diesels to the US because of differences of opinion on emissions too. But then a few years later they start right back up importing them.

But hey, back to the important stuff. As a rule, my dad's tougher than your dad, my Ford's better than your Chevy, and my Mom's prettier than your Mom. Period!

Ken
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Old 01-13-2012, 02:10 PM   #22
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How difficult is it to find good, reasonably priced service today?

One can wonder how long you'll be able to get parts for a model T too. You can build a complete 57 chevy from aftermarket/nos parts. I wonder how long that will be available? I tried to get a windcup for my Careless of Colorado awning that is 3 years old and it's obsolete and unavailable from the factory. Guess we should never buy an RV with one of those either. Mercedes has stopped importing their diesels to the US because of differences of opinion on emissions too. But then a few years later they start right back up importing them.

But hey, back to the important stuff. As a rule, my dad's tougher than your dad, my Ford's better than your Chevy, and my Mom's prettier than your Mom. Period!

Ken

Let's play another game shall we? Let's review the last 10,000 or so posts on here, and on other similar sites. Do you see tons of posts extolling the virtues of rv related products and patting lots of service providers on the back for a job well done? Didn't think so. OP is asking a question related to purchasing a Coach and I think the engine is a major consideration, especially these days? "Bigger is better" not only refers to cubic inches it can also refer to the Manufacturer. Cummins looks like it's in this for the long haul, continuing to cater to Motorhomes and rv Dealers. I have a Guy not far from here who I think is a magician with Diesel related items. His yard is full of cranes, dozers, excavators, trucks, etc. and he can make 'em all run, and for a fair price too. Problem is his yard is full of cranes, dozers, ............. not many motorhomes. He worked on mine once and he did a great job; unfortunately whoever did the work forgot he was working in my "home" so it came back filthy. Yes, you can get Mercedes parts; priced any lately? I'm trying to provide practical considerations for a prospective Owner, not compete with anyone so please don't think I am.
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Old 01-13-2012, 02:33 PM   #23
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SOLUTION;
1, Buy somthing that is currently being manufactured and not been bought out.
2, Call their tech line and see if they are helpfull and have parts for your model.
3, Make sure the engine has at least 330 horse power and 860 pounds of torque
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Old 01-13-2012, 02:51 PM   #24
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The last thing I would consider when buying a RV is the engine size. The layout is SO much more important.

I have a gas engine on a 36' RV and have managed to get around the U.S. a couple times and drive in western mountains all the time.

I've never seen an RV that couldn't climb a mountain no matter what size engine it had in it.
X 2.
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Old 01-14-2012, 10:59 AM   #25
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Let's play another game shall we? Let's review the last 10,000 or so posts on here, and on other similar sites. Do you see tons of posts extolling the virtues of rv related products and patting lots of service providers on the back for a job well done? Didn't think so. OP is asking a question related to purchasing a Coach and I think the engine is a major consideration, especially these days? "Bigger is better" not only refers to cubic inches it can also refer to the Manufacturer. Cummins looks like it's in this for the long haul, continuing to cater to Motorhomes and rv Dealers. I have a Guy not far from here who I think is a magician with Diesel related items. His yard is full of cranes, dozers, excavators, trucks, etc. and he can make 'em all run, and for a fair price too. Problem is his yard is full of cranes, dozers, ............. not many motorhomes. He worked on mine once and he did a great job; unfortunately whoever did the work forgot he was working in my "home" so it came back filthy. Yes, you can get Mercedes parts; priced any lately? I'm trying to provide practical considerations for a prospective Owner, not compete with anyone so please don't think I am.
It looks like we agree that "good" service is hard to find even now and regardless of brand. Your example of your diesel magician obviously left a bad taste in your mouth. I think there are good mechanics that do understand how to treat a MH. It's just a matter of finding one, regardless of which engine you have. Don't you think a good general diesel mechanic would be able to change injectors, oil, alternator, starter, etc on a Cat as easily as a Cummins?

I agree with you that an OTR dealership may not understand the mechanic has to walk thru my living room, kitchen, bathroom and into my bedroom to work on some parts of the engine. OTR guys are used to flipping up the hood and leaning back against the tire, not worrying about the dirt on their coveralls.

I'm not familiar with Cummins dealer service network since I don't own one, (other than my generator) but do they have a series of dealerships that are RV specialists like Cat does? Cat lists their dealers by their specialties, electric generation, marine, truck engine, railroad etc. so you can select a dealer that knows how to treat an RV. I think for a prospective owner that might be a practical consideration just as you state in your post. (CAT RV Centers) The Cummins URL would be a good site to post for new buyers so they are aware of the dealership service that caters to Cummins RV owners. I did a quick search for a Cummns site similar to the one I gave above for Cat but it didn't pop up.

Actually I haven't bought any Mercedes hard parts for a few years. I bought a throttle potentiometer, because they're all electronic, no cable or linkage, go out 3 or 4 years ago and it was a couple hundred bucks. Not too unlike the electronic linkage in my MH. I also replaced a muffler hanger rubber a while back too, but it was only $4.00 or so. I replaced the front brake pads and rotors. The pads are metalic and pricey at almost $50.00 and the rotors were $70. Thanks to the separate hub/rotor design the rotors are pretty inexpensive compared to other cars.

Other than that I have just regular oil changes and lube work done on my Mercedes. It's amazing once you start really looking at them the amount of intelligent design and communication MB puts in their cars. They tell you that the door hinges need greased, the sunroof slides and latches need lubed, hood and trunk hinges, etc. for a long lasting service life. I've been satisfied with and buying Mercedes S class cars since 1990.

Ken
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Old 01-14-2012, 11:58 AM   #26
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The last thing I would consider when buying a RV is the engine size. The layout is SO much more important.

I have a gas engine on a 36' RV and have managed to get around the U.S. a couple times and drive in western mountains all the time.

I've never seen an RV that couldn't climb a mountain no matter what size engine it had in it.
If you LOVE driving, and performance matters,get the biggest engine you can.
If you drive because you have to and enjoy driving at 55mph, engine size doesn't matter.
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Old 01-16-2012, 07:49 AM   #27
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I agree with vito.a, "torque" is what you need to move big, heavy rigs. Our 38' Gulf Stream with a 350HP ISC Cummins has over 1000lbs/ft of torque and averages around 10MPCanadian Gallons. It climbs mountains with some loss of speed but less loss than many big transport trucks. And most 'big' diesels are rated as "million mile" engines as they don't 'grunt' as much as smaller diesels do to do the same amount of work. Good luck on your purchase.
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Old 01-18-2012, 08:01 AM   #28
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We done a lot of shopping.. Which is best ??? Well we/I found the best place for engine information (diesel) was at a truck stop. I talked to 1000s of them. Here's what I came up with. Would you buy a Big mack truck If you only needed a VW.. The Cat 300/330 (has the same torque) Is what the truckers call the Baby cat. Good for about 500000 Thousand miles. A lot of them like that engine. Cat/comm. Equal, And they (truckers) say that the Fuel mileage is better; We have a 330 DP tow a full size car No problem.. When I here someone say they need 400/500 HP in a motorhome. They need to readjust there driving habits and there schedules;; My neighbur Has a big thuck , Uses it to go to work , JUst him. Now I see that as a true waste. He could be driving a little compact Saving our resorces;; However it is a free country;; So you buy what you want, Some think they need 165 hp some think they need 500 hp. That is just fine. Which ever you get you will be happy. At times you will want more power and or fuel mileage; Life is good
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