Is a Cummins ISB a bad way to go ?

[michguy]

I desperately need your advice. I have received so many conflicting responses to questions re: the Cummins ISB engines that I don't know how to proceed. We are going to buy a 36 ft. - 40 ft. used Diesel Pusher. I see so many of these with Cummins 300 HP Diesel engines. I've been assuming that all of these are the ISB engines, and that I shouldn't buy a coach with this engine. My question is, "Why not?" Is the engine overtaxed ? Is it more apt to break down ? If I pull a 2007 Saturn Aura, am I asking too much from it. I do intend to travel in the Rockies, the Adirondacks, the Alleghenies, Blue Ridge, Wasatch and various California ranges as well. But, that will not be my exclusive use. I'm aware that I won't climb the mountains with the same gusto as those with a 400 L model, but that doesn't concern me. What does, is if the engine is subject to more major repairs and problems than the ISC's & ISL's. Please, somebody give me some answers. I'm passing up some fine coaches due to this situation.
Thank you,
Michguy

[RustyJC]

Where exactly are you getting your information regarding the reliability of the Cummins ISB engines? In the size coach you're considering, some might consider them underpowered, but much of that depends on your expectations. The 5.9 liter and later 6.7 liter Cummins B-series engine has a long history dating back to the early 1980s. They've been used in both on-road and off-road applications powering not only motorhomes but agricultural equipment, military applications, generator and pump sets, school buses medium duty trucks and much more. Unless an engine has been modified with aftermarket components for more power, Cummins' factory calibrations are designed to keep the engine out of trouble, even if you climb the Rockies with the accelerator pedal on the floor.

If you'll cite the particular problems you're hearing about, we'll be glad to address them.

Rusty

[Automobilist]

Our previous diesel pusher was a 2001 35' Forest River with the ISB / 5 speed Allison. Way, way, WAY underpowered. 260hp & 520 lb ft torque. Not nearly enough to push 22k of coach. The basic motor is fine, works great in Dodge pickups. Torque is where its at in motorhomes, and the ISB doesn't cut it. Our current coach has a Cat 7.2L, with 860 lb ft of torque. Realistically, I wouldn't tow much of anything with an ISB.

[fun time]

I have owned two and currently have a 36ft. Meridian with the 300hp. Never had a problem, great fuel milage. Enough said. You have to make the decision and no one can make it for you.

[srydve]

I have a 34' Kountry Star with a 300 hp ISB, I pull an extended cab Ranger pick up. I have no complaints with any aspect of the ISB. Sure you could have a unit with a bigger motor and more power and torque, if you're the type that hates anyone going by you in the passing lane then you won't be happy with the ISB. If on the other hand you can be satisfied with getting there in reasonable fashion I don't believe there's any reason to avoid one.

[hooverbill]

[QUOTE=Automobilist;811635]Our previous diesel pusher was a 2001 35' Forest River with the ISB / 5 speed Allison. Way, way, WAY underpowered. 260hp & 520 lb ft torque. Not nearly enough to push 22k of coach. QUOTE]

Agree. That's not enough for a pick up much less a MH. I had a Chevy with the Duramax that had 100 more HP and 130 more ft/lbs of torque. I don't know, but maybe the ISB is considerably cheaper than an ISC or ISL.

[RustyJC]

Quote:

Originally Posted by michguy I'm aware that I won't climb the mountains with the same gusto as those with a 400 L model, but that doesn't concern me. What does, is if the engine is subject to more major repairs and problems than the ISC's & ISL's.

To address your specific question as you stated above, no, it's not.

Rusty

[JManatee]

We have the ISB 325hp in an 38' (33k gcwr) and tow a honda CRV, we have towed all over the north east. Including the white mountain area... Its not a race car, but I am often passing trucks on hills.

We average just under 10mpg. I am happy with my ISB

[gknott]

We had a 98' 36' discovery w/ ISB 275hp and 660 torque and 6sd trans. Pulled Jeep Grande Cherokees
Had lots of power,not many hills it wouldn't pull in 4th at 1800 to 2000 RPM.(25000#GCVW).Good fuel economy

[Parkerrs]

Good fuel economy = Yes
Will "do" the job = Yes

More problems or repairs = No
More costly repairs = No
Major trouble = no

The C and L series have much more torque and pull like a bull. They also give worse fuel economy which is the trade off for the power. The B is a fine engine, but until you drive similar length and wieght coaches with each engine you can't make an informed decision.

Drive similar coaches with each engine and then decide for yourself what you can live with. I've been told the units with the B get around 10mpg, I know from experience the L will get in the 7-7.8mpg range and I haven't talked with anyone running a C.

All three are good engines and will do the job for the life of the coach when properly maintained.

[ernieh]

A good rule of thumb is nothing less than 20ft/lbs of torque per foot of coach. Anything less is going to be pretty slow going in the hills with a toad. 23 to 25 per foot will take you anywhere "with style".

[southland]

I have a 300 ISB in a 35 ft unit. No problems other than fuel (my Fault).
No oil burned during a 10k mile trip.
Did wish for another 50 or so horses while in the mountains but got there just the same.
Fuel mileage is good for a MH.
Good luck with your choice.
Jerry

[Dacotah]

Before we bought our 2001 38' Sportscoach, we did some engine research and like most of the comments here, it depends on who you ask. We have the 275 HP ISB and it is very economical; without towing we get 11.2 MPG at 64 mph, but we live in Florida without any hillls. I expect the mountains will be very slow, but on the flat land it has enough power for us. We havew owned many gas coaches over a 20 year span but this is our first diesel. My research showed that the ISB is very reliable, easy to work on and parts are inexpensive. Also, Cummins has great support for do it yourselfers like myself, and I joined the Cummins power club which gives 10% off on parts and labor. An older coach like mine with only one slide out does not weigh as much as the new four slide ones either. DACOTAH

[michguy]

Thank you everybody. I'm certainly not afraid of the 300 HP ISB's anymore. It would be nice to have power to burn, but the increase in fuel economy means that I'll have more money to burn.