Diesel Pusher Engine Recommendation

OK, I'm new to the forum but not RVing.  Over 20 years we started out with a Class A Winnebago, went to a Class C Tioga, towed a 30' travel trailer, and now have a 5th Wheel.  Next up is a 36 - 40 foot diesel pusher.  Looking at late 90's, early to mid 2000's DP, I like HR, Winn, Itaska, etc., freightliner chassis looks good, the piece of the puzzle is what engine to look for.  Older models seem to like Cummins 275's, as the years progress more engine choices appear, and in general, advertised HP increases.  Driving will be a mix of flats and mountains, including the Rockies, towing a small car.  My main concern is HP, I don't want an underpowered rig that makes me regret it while I'm grinding up some mountain pass nor do I yhink I need the largest engine out there if I'm not going to need the HP at the expense of MPG.  I've done some searching here on this vast forum, but still not certain I know what you experienced DPers would advise as an engine choice.  Any thoughts would be appreciated. 

We have a 2005 Holiday Rambler with the ISL  Cummins, 400 horse. Just love it. We tow a Honda CRV and do not even feel it being towed. The coach is rated to tow 10,000 pounds. Every year for the last 4 I have driven the speed limit on the way to Arizona, 70, 75, etc. This past season I drove 65 all the way, and what a difference in the fuel mileage. Had to see for myself, I had quite a bit more fuel in the tank at our regular fuel stops. I really do enjoy this engine and recommend it. The reason I bought it was because of the larger engine and towing capacity.

Great input, thanks very much.  I guess I should also have asked for any MPG experience anyone wants to volunteer as well.  Regards,

By way of comparison, my previous coach, a 2006 Fleetwood Expedition 38', with a C-7 Cat at 300hp, weighed 26,320 wet. The new coach, a 2012 Thor Tuscany 42', with a Cummins ISL 8.9 at 450hp, weighs 35,510 wet.

The Cat would never get better than low 7's for MPG, while the Cummins consistently gets 8 MPG and change, a pleasant surprise.

We drive the mountains of the West and the difference in the weight to horsepower is quite noticeable. The Cat was puffing at the top of long grades, the Cummins not.

A friend recently went from the 275hp Cummins in his old coach to a larger engine in another coach because he never felt like he had the horsepower he needed in the west pulling his Jeep.

It makes a difference where and how you drive them, your loaded weights, horsepower to weight, etc.

Pilots and racers will always say there is no substitute for cubic horsepower!  8)

Another consideration, and I don't know the years applicable but with the 340hp motor (on the newer units) you get the Allison 2500 trans which has a lower lowing capacity. Engines with 360hp and above have the Allison 30000 trans. If memory serves me I think there's a 5000 lb towing difference in the 2 trannies.

One other consideration is I believe all newer diesels, 2007 and up, use Urea injection for cleaner exhaust. Meaning you have to fill a holding tank with urea every so often to keep running properly. This is an extra expense on top of diesel fuel fill ups. Not sure of the fill up schedule for urea though, others here could help with that.

Engine should not a major consideration when choosing a motorhome, but if you want a rule of thumb look for at least 1hp/100# of GCVW.  There are more important things to look at like floor plan, condition (if used), price, amenities, and to some extent the chassis.  Satisfy yourself with those items and don't worry about the engine as it won't be an option.  If buying new, Cummins will be the overwhelming make since Cat left the on road engine business.  MPG isn't a factor of the engine but mostly by your driving technique and, to a lesser extent, the GVW.

In the model year rigs you're looking at there will be lots of Cats and Cummins. Both are good engines, for the area you'll be traveling you want 400 HP to go up hills at a reasonable rate and get reasonable mileage. The 525+ hp engines are enticing but not necessary.

As one poster said 2007 and newer ENGINES require the urea additive, which is an every couple or few thousand mile event. Not a big deal in the long run. DEF is widely available and it's a simple matter to pour into the onboard tank. Now why did I emphasize ENGINE, because there are many 2007 model year rigs with 2006 engines which don't need the DEF.

Ken

We have a 2005 Winnebago Journey 34ft with a 300hp Cummins engine on a freightliner chassis.  No complaints here.  We have towed a Honda CR-V for a few years with no issues.  We average about 8.5 MPG.  On very steep grades, we are going about 40 MPH nearing the top, but not stressing at all.  The engine and tranny are pulling the grade at that speed with good RPM's.  If you want to fly up all the grades at full speed, you will need more hp.  But if you can deal with some loss of speed on grades, the 300 should be adequate.  Also keep in mind I'm only 34ft, which probably makes some difference compared to a 40 footer. JM2C

Steve

You said you were looking at late 90's or early 2000 coaches, so I'll chime in.  I have a Fleetwood American Dream that has the Cummins ISC 8.3L engine at 330 HP.  GVWR is 32,000 lbs., GCWR is 42,000 lbs., actual loaded weight is about 29,000 lbs.  I tow a Prius on a tow dolly that weighs about 4,000 lbs., so my actual traveling Gross Combined Weight is about 33,000 lbs.  As Ned said, a good rule of thumb on HP to weight ratio is to have 1 HP per 100 lbs. Gross Combined Weight, so I'm right on the money.

That being said, if you like to go fast and storm up mountains, more horsepower and torque is going to get you that.  Mine does just fine up the mountains and I'm not in that big a hurry.  The biggest factor in getting better fuel economy is going slower.  I can go 70 or 75 MPH if I want to, but my fuel economy suffers greatly.  For me, between 60 and 65 MPH gets me the best fuel economy and still gets me there in good time.  I average about 8 MPG going this speed and towing my car.  Going 55-60 without the car, I can get 9 or a little better and going 70 t0 75 with the car I'll get 6 or so.

Hope this gives you some ideas.

Dan

We have a 425 HP CAT C-12 in a 32,000 pound MH and ours acts more like a sports car than an RV.  With a 3,500 lb toad the CAT hardly notices most hills.  We can climb any grades on the interstate and still be at ~53-55 at the top.  I'm rarely in the truck lane because it's too slow and I can't maintain momentum.  Is this much power necessary?  Of course not, but it's a lot of fun to drive.  We get a very consistent 8-8.5 mpg under almost all conditions with an average cruising speed of ~63 on the interstates (that's how fast I have to go to get the Allison into 6th).

One thing that hasn't been mentioned yet in this thread is that you need one of the larger engines (C-12, ISL, ISX) in order have a compression brake rather than an exhaust brake (and not all ISL's have them).  I'm not disparaging exhaust brakes, but I doubt that anyone would argue that they are no competition for a compression brake.  My engine can develop >300 HP of stopping force with its Jake brake and it's a wonderful feeling going down mountain grades to have to give the engine some fuel to maintain speed because the MH is slowing down so much.

billwild said:

One other consideration is I believe all newer diesels, 2007 and up, use Urea injection for cleaner exhaust. Meaning you have to fill a holding tank with urea every so often to keep running properly. This is an extra expense on top of diesel fuel fill ups. Not sure of the fill up schedule for urea though, others here could help with that.

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Actually urea post exhaust treatment did not come into play until 2010 model year engines.  In 2007 the EGR and DPFs (diesel particualate filter) come into the market although you may not see these engines until 2008 model years becasue many manufactureres had overbought 2007 engines and were allowed to run them in 2008 coaches.

As far as engine size, one horsepower per 100 pounds is a good rule of thumb to start with.  Any engine will get you up the mountain passes it is just that some will do it easier and a little faster than others.  One thing to keep in mind is as the coaches get bigger with more amenities such as hard surface countertops, solid cabinets, larger chassis (ie more weight) the engines also get larger but power to weight doesn't change as much as you would think.

There are some "hot rods" out there that may have an ISL400 in a 28k pound shorter coach but they are far and few between.

For examble our previous coach was a 38' Beaver Contessa with the old 300HP 3208 CAT with Allison MT654 four-speed transmission weighing right @ 29k pounds and towing a 24' enclosed trailer weighing 8500 pounds would pull a 6-7% (Malad Pass in Northern Utah) at 37 mph.  I would just tuck in line behind the semis and go with the flow.

Our current coach, 40' Dynasty weighing 36k pounds towing 12k pounds of 26' enclosed trailer with toys will pull the same grade around 47-50 mph.  A little faster but also a lot heavier rig.

There is nothing wrong with the either CAT or Cummins engines so either one would not be a deal breaker providing the power to weight is within the range mentioned above.

Mike.

This is all great input, I feel like I've got something to work with now.  The HP to weight ratios are very informative, as is the MPG experience you folks have had.  Thanks very much and anyone else who wants to chime in please do so.  Thanks very much.

Regarding Cat and Cummins, are there any year or series upgrades I should look for in the early 2000's engines. For instance was there a better fuel system implemented in 2003 and so on?  Thanks

There have been two major changes in engine performance due to EPA regs. One took place on 1/1/2007 and another on 1/1/2010. Before that, not much happened since the transition from mechanical controls to electronic in the late 90's. Pre-2007 engines generally get noticeably better fuel mileage that later ones. Note that a 2007 or even a 2008 motorhome may have been built with a pre-2007 engine. Chassis manufacturers stockpiled the 2006 engines and used them for many 2007 chassis, and then RV manufacturers stockpiled some chassis to use in later RVs.

Gary, one outher milestone was in 2003 when Cummings went to the electronic controlled high presher commen rail system.
Bill

This series of ISL engines had a potential connecting rod failure that they applied a band-aid fix.....http://www.allworldauto.com/recalls/NHTSA_07E033000__CUMMINS_ISL_CM850_recall_69420.html

in 2003 when Cummings went to the electronic controlled high presher commen rail system.

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Yeap, though I don't think that has any significant effect on owning/using one.

Someone mentioned weight to horsepower ratio and that's a consideration if you are performance oriented. Some people find the acceleration of their motorhome frustrating compared to their car. If you are one of those, look for a weight:Hp ratio of better than the typical 100:1, e.g. closer to 80:1. Measure it using the estimated loaded weight, including any towed load.

If you think you may want to tow something that weighs 5000 lbs or more, make sure the rigs you consider have adequate tow capacity. Most gas-powered chassis are limited to 5000 or less, and some diesels may also be in the 4000-6000 range (but 10,000 or better is more typical of a diesel pusher).

bucks2 said:

In the model year rigs you're looking at there will be lots of Cats and Cummins. Both are good engines, for the area you'll be traveling you want 400 HP to go up hills at a reasonable rate and get reasonable mileage. The 525+ hp engines are enticing but not necessary.

...
Ken

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Whether 525+ is necessary depends a lot on weight -- my 2007 Beaver with 525 HP isn't all that sprightly, but it's 42,000 empty, w/50,000 lb max for the coach. It needs that 525.

BugDuckley said:

My main concern is HP, I don't want an underpowered rig that makes me regret it while I'm grinding up some mountain pass nor do I yhink I need the largest engine out there if I'm not going to need the HP at the expense of MPG. 

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This old retired truck driver spent a lifetime pulling freight all over east of the Mississippi River, in places like Pennsylvania, West Virginia, western Virginia, and western North Carolina, including the old Trail of the Lonesome Pine into Kentucky, in old, worn out, underpowered diesels like Detroit 238s, before hauling regional bulk petroleum products.  I think my '94 Cummins mechanical 5.9 has all kinds of power today!!!  It may not go up hill as fast as the new Cummins 600, but it will get the job done.  And mpg - I'm getting 10 to 11 mpg overall pulling my toad and weighting about 24,000 lbs.  Yes, the coach is light, but it is very nice for being 20 years old.