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Old 07-20-2021, 10:08 AM   #1
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Which Cummins engine ???

Hi all, looking at some coaches in the 37-40 ft length. Are there any "better" engines I should add a few points for ? Any I should steer away from ? I understand the higher the torque the better power for mountain driving but there seem to be a LOT of different ones. Thanks, Ken
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Old 07-20-2021, 10:13 AM   #2
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About how old? Are you looking new or used?
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Old 07-20-2021, 12:18 PM   #3
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Quote:
Originally Posted by kengardner View Post
Hi all, looking at some coaches in the 37-40 ft length. Are there any "better" engines I should add a few points for ? Any I should steer away from ? I understand the higher the torque the better power for mountain driving but there seem to be a LOT of different ones. Thanks, Ken
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Originally Posted by dizcom View Post
About how old? Are you looking new or used?

The questions by discom are important as they will change the available choices.


In general, assuming you are asking about diesel engines, that size coach can have anywhere from a sub-300 hp engine to over 400 hp. The engine could be a CAT or Cummins, though you are asking only about Cummins, but the CAT is only in older coaches. Which ever engine you find, they are all robust and reliable, but each will have possible issues based on the particular year and model. You'll need to ask when you have a specific engine in mind.


Over all, the rule of thumb is to get an engine with 1 hp for every 100 lbs. of coach GVCW. Again, general rule, but gets you in the ball park.


For your range of sizes, you will find anything from an ISB to an ISL. All are good, but all have issues, depending on the year. The ISC is a real workhorse that would be the smallest I would consider in the larger coach. The ISL is essentially the same strong engine with a longer stroke. A great engine.


A Cummins ISC or ISL, built prior to 2004 model year, will have the CAPS fuel injection system that was later replaced by the newer, more reliable, Common Rail. CAPS should not be a deal breaker as long as the lift pump has been maintained and/or replaced and monitored regularly.


Rather than go through the weaknesses of certain engine models, it's better to wait for your proposed choice to be mentioned. Then, you will get many responses as to what to look for or what to avoid.
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Old 07-20-2021, 12:35 PM   #4
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I have the 8.3 with 360hp & a bit over 1,000 in torque for my 42í MH. I get 8mpg and all the power I need for the mountains. Just under 60k in mileage and annual maintenance is all it has needed.
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Old 07-20-2021, 02:16 PM   #5
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Cummins engines

Oops, left out critical info. I havenít narrowed my choices down but will look for a Cat if I go with pre 2009 . Wife is nervous about the older coaches and likes the 2014-2018 models. We had a new 2014 Coachman Mirada gasser a few years ago and were extremely disappointed in the poor quality. Iím fighting hard for a pre 2009 top of the line coach but want to drive a few of her choices too.
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Old 07-20-2021, 02:26 PM   #6
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Originally Posted by kengardner View Post
Oops, left out critical info. I havenít narrowed my choices down but will look for a Cat if I go with pre 2009 . Wife is nervous about the older coaches and likes the 2014-2018 models. We had a new 2014 Coachman Mirada gasser a few years ago and were extremely disappointed in the poor quality. Iím fighting hard for a pre 2009 top of the line coach but want to drive a few of her choices too.
This post does help.


2014-2018 intrudes on the post 2016 DEF issues that are currently a very hot (in every sense of the word) topic. Freightliner chassis do not seem to have such a major issue. Spartan does.


2014-2016 (coach model year, not engine year as a 2016 coach may have an earlier engine) are a good bet. Still have DPF and DEF, but with less complex system and fewer failures. Over all, the coach should be your consideration, not the engine, as you noted with your Mirada. Lots of high quality coaches in those years with decent fit and finish, plus most kinks have been worked out or replaced.
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Old 07-20-2021, 02:56 PM   #7
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kengardner --

I've learned from other forum members on iRV2 and FMCA forums that the "rule of thumb" for engine size is 100 HP per 1000 lbs. GVWR to maintain affordability of a coach Hence a coach like mine (single rear axle) that has a GVWR of 36,000 lbs. the typical engine size would be 360 HP. Hence I have a 360 HP Cummins ISB 6.7L engine pushing my coach down the road.

By contrast the same floor plan 2016 Newmar Ventana with tandem rear axles has a 44,000 GVWR for which Newmar uses the 400 HP Cummins ISL 8.9L engine.

I've yet to drive in the Rocky Mountains so I don't know how my engine would perform in those conditions. I-10 through the Texas Hill Country does have some moderate length hills with 6-7% grade. Climbing those hills I drive faster than semi-trucks but slower than an F250 thus I say my 360 HP engine is just "OK".

Hope this info is helpful.
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Old 07-20-2021, 05:38 PM   #8
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You do not want a Cat that has a dpf. That would be a 2007/8. The earlier c7 and c9 are great. It is hard to find the right coach with the right engine.
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Old 07-20-2021, 05:49 PM   #9
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Our '02 40' with tag axle coach... GVW is 42k.(combined/towing 52k) has a M-11/ISM-11 Cummins..500 hp 1,400+ torque... 7mpg to 8mpg.
I Strongly Suggest that You concentrate on '00 to '07 Year models to avoid all the environmental exhaust treatment add on BS..
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Old 07-20-2021, 08:55 PM   #10
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After a lot of research on my end I went with a ISM. I found out that they are the bigger Cummins for coaches I have a 2000 Monaco.

I donít see as many post with issues on the ism and isx not sure why the only thing I can think of there larger engine so they have less work to do for bigger coach.

I personally would not have a 40í coach without a tag and an ism/isx or big DD 13,15,16.

I believe the bigger the better and the less strain on the power plant.

Donít forget the transmission needs to match but I hope the mfg did it right.
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Old 07-21-2021, 08:20 PM   #11
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I must have bought in the right year diesel. My 14 ISL9 has been very reliable, gets 8+ mpg, Is a non polluter. DEF system is not the later ones with unreliable heads. No Fass system. No dropped Valves. Starts after sitting for months. No gauge problems, clean CAC and rear radiator. And best of all is a heck of lot quieter than older diesels. You can have your old diesels.
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Old 07-21-2021, 09:31 PM   #12
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^^^^^^ What he said. My "15" isl9 has been 100% bullet proof. Def system is still stock from the factory.
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Old 07-26-2021, 08:35 AM   #13
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While looking, also note that depending how the Coach Manufacturer spec/ordered the chassis/engine, an ISL could have either Exhaust Brake or Jake Compression brake assist. Usually, the higher up the model food chain, gets you the Jake Compression, which IMO is preferable to Exhaust Brake.

Good luck on your hunt,
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Old 07-26-2021, 08:14 PM   #14
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Originally Posted by Smitty77 View Post
While looking, also note that depending how the Coach Manufacturer spec/ordered the chassis/engine, an ISL could have either Exhaust Brake or Jake Compression brake assist. Usually, the higher up the model food chain, gets you the Jake Compression, which IMO is preferable to Exhaust Brake.

Good luck on your hunt,
Smitty
Yup.. Even tho our Foretravel has the Allison 4060r transmission with the Allison hyd retarder, I still miss the Jake..
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