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Old 04-25-2021, 11:11 AM   #1
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ISB 6.7l

Any comment's on this engine??
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Old 04-25-2021, 11:27 AM   #2
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Quote:
Originally Posted by Long Island Mac View Post
Any comment's on this engine??
Off the top of my head, that engine is an evolution from the nearly bullet-proof ISB 5.9 which is a parent block engine that does not have cylinder liners. The 6.7 came into being for needs to meet the newer emission requirements thus, depending on the year of manufacture, will have ERG valve and cooler along with a Diesel Particle Filter and DEF. All the 6.7 ISBs are High Pressure Common Rail fuel injection. Note that since the 6.7 was designed for use with emission controls, the way the engine is used must be altered, just like on all other diesel with those controls. Endless idling is discouraged due to clogging of the DPF, for example.


My only concern would be the power to weight ratio of that engine in a motorhome. No diesel pusher is an acceleration fiend, but a 33K lb. motorhome pushed by an ISB is a lesson in patience. If the same motorhome offered a larger engine, say an ISC, I would jump on that. However, if you're looking at older coaches that have an ISB, it's definitely not a deal breaker, IMO.


In short, it is a well proven engine used in literally thousands of pick up trucks as well as motor homes. Parts are easily obtained and is a well respected engine in the repair community.
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Old 04-25-2021, 11:59 AM   #3
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My RV has an ISC, but I just drove an ISB 6.7 powered (with Allison trans) rental truck 1200 miles a few weeks ago. Fully loaded 26’ box truck towing a car on a dolly. The truck did really well through the mountains, and got over 11 mpg. I used the engine/exhaust brake (I’m assuming it had an exhaust brake), and I didn’t have to touch the brakes going down big hills.

It was a really smooth running engine. Penske had it setup to only idle in park for 5 minutes before it would shut itself off. I used around 3 gallons of DEF on the trip.

I wouldn’t hesitate to get an ISB in a smaller class A. IMO it’s definitely an upgrade over any gas engine.
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Old 05-01-2021, 08:35 AM   #4
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Originally Posted by Long Island Mac View Post
Any comment's on this engine??
Works great, lasts a long time.
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Old 05-01-2021, 08:48 AM   #5
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My RV has an ISC, but I just drove an ISB 6.7 powered (with Allison trans) rental truck 1200 miles a few weeks ago. I used the engine/exhaust brake (Iím assuming it had an exhaust brake), and I didnít have to touch the brakes going down big hills.

If late model, likely a VGT (Variable Geometry Turbo vs exhaust brake. They work similarly.
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Old 05-01-2021, 08:58 AM   #6
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I was really leery about a smaller diesel in a DP, but options for a small Class A are limited. Power to weight is important but so are driving style and habits. After spending a year or so studying mid 30’s class A rigs, I settled on a 34’ Ventana with an ISB. It is slow off the line, and I’ve learned to anticipate when it will start rolling and I start accelerating a little early - works for me but timing is everything. Once rolling it does just fine. I don’t wait for it to downshift on grades, because it will always be too late, unless I really don’t care if I end up in the mid 40’s mph.

I also found, after a couple runs over the Tehachapis, that if I hit the grade at 70 I could maintain it (although probably at 2-3mpg), but if I started up in the low 60’s (where I normally drive) I’d end up in the low 50’s mid-way up the hill. 50’s is fine with me, and it works well with the truck traffic - I’m a little faster than most of them and of course, slower than the cars, so I anticipate when I’ll need to pass and work with both traffic patterns to keep moving while not being a nuisance.

So it’s been a learning thing. The longer I have it the better it seems to perform but it’s really just me getting used to it’s limitations and learning to stay in the power curve (1800-2200 rpm). It also gets over 9mph when you go easy on it which is pretty nice given a 100 gallon tank - I never have to fuel up more than once a day.

I’ve also towed 4000+ lbs over the Sierras and also all the way from Richmond Va to Northern Ca, and found very little reduction in performance on grades - maybe a 5mph deficit. Again, it takes planning and a little OCD on the shift pad, but it works. With an ISL I’m sure you could just put the cruise on and ignore everything. But you’d also be in the 7mpg range, and in the long run probably wouldn’t get where you’re going much sooner, which isn’t an issue for me anyway.

The big issue is power to weight ratios. Do the calcs and see what you get with similar rigs equipped with both engines. The ISL will always win, but those rigs weigh around 6000lbs more to start so the results aren’t always that dramatic in HP; more so with torque.

I drove a 2008 34’ Country Coach with a Cat C9 and while it may have held speed better on a grade when towing (didn’t try that), it did no better around town or on the local highways than my 6.7 34’ Ventana which weights only 28k empty. In fact it seemed a little doggy by comparison. Drove nice, but so does the Ventana.

Maintenance is about the same, oil changes are 18-19 qts, takes about 20 min (I do it at 7500 miles), air and fuel filters, and cooling system, have the same maint interval. Transmission is the same - most ISL engines are mated to a 3000mh. One big plus you get with most (but not all) ISL rigs is a side radiator. I’d prefer that but was willing to give that up for the other benefits of a rig this size. Another is a Jake - also preferable, superior to the VGT system, but not a deal killer.

The only real drawback is emissions as noted above. The SCR/DPF/DEF system is poorly designed, over engineered, and problematic. You have to be very careful with its care and feeding and it can leave you stranded for no logical reason or actual fault. There are volumes written on this. I’ve learned to deal with it and I think I’ll be ok, but it sure gave me some trouble early on. Hopefully as we enter the second decade of these systems, they will figure out how to make them reliable soon. Hopefully.....
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Old 05-01-2021, 09:27 AM   #7
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I have a 2007 cummins 5.9L ISB rated at 325HP with 6 speed Allison 2500 in my 2008 Monaco Cayman 35ft. No DEF and no DPF. It's power band is 1800-2200 and has no trouble with a 33k lb total rig. It can rev higher but I don't push it that hard. Average 10mpg and have traveled Maine to the FL keys and across the Appalachian mountains in Tennessee. It accurate to say you just have to anticipate the hills and use the engine brake for down hill. Very pleased with its overall performance. It's not up to the requirements of a 40 ft rig but just fine in a 35 ft unit.
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Old 05-01-2021, 09:31 AM   #8
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I have a 2007 cummins 5.9L ISB rated at 325HP with 6 speed Allison 2500 in my 2008 Monaco Cayman 35ft.

2007 ISB is 6.7 liters, not 5.9 liters.
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Old 05-01-2021, 10:22 AM   #9
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No my 07 ISB is 5.9L
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Old 05-01-2021, 10:23 AM   #10
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The 6.7L is 340 hp
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Old 05-01-2021, 10:31 AM   #11
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No my 07 ISB is 5.9L
This^^, would be consistent with your description of the lack of emissions systems on your engine. No doubt, your coach has an older chassis/engine which was typical. The 6.7L ISB was built and designed for the addition of DPF for the 2007 build requirements. I would suspect, however, that your engine does have the ERG valve and cooler.


If you have a 2008 Cayman, it's quite possible the engine is from 2006 or earlier. Best way to settle this discussion is for you to check the ID plate on the engine.
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Old 05-01-2021, 10:55 AM   #12
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The 6.7L is 340 hp
It comes in two versions - 340/700 and 360/800. The Winne Forza and
and the Newmar Ventana LE models 37’ and under had the 340hp, as do a lot of super C coaches, and the new front engine diesel Canyon Star.

The Ventana (34 and 37 models) as well as the new Kountry Star, come with the 360/800 as do the 33’ New Aire models and others. I’ve always thought it would be easy to up the 340 to 360 since it’s basically the same engine. 20hp isn’t that big a deal, but 100 lb-ft of torque is.
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