Choosing Gasoline or Diesel Powered?

[JohnnyT]

I realize that this is a long thread but if you are pondering the Gasoline versus a Diesel based on power consideration or are wondering about adding an after market performance enhancing kit to a Gasoline engine to close the power equation it might be worth a read. This thread is intended to be an addendum to the First Time Buyer... sticky.

The question of a Gasoline versus Diesel is a topic that seems to have no correct answer. But one that comes up frequently Here is some food for thought, after you have done some looking post questions about specifics and you will get plenty of feedback.

Diesel can have more torque and HP but that does not always translate to better performance and higher MPG. There are some configurations of Gasoline powered Motorhomes that will out perform some Diesel coaches due to weight to power ratio, gearing, rear axle ratio. There are some diesel powered configuration where power is not an issue with any grade or load.

In terms of reliability Diesel engines are constructed to have a longer life span but for most folks and I mean most, the reliability and longevity is sort of a non issue due to the amount of mileage and the length of ownership. Diesel's will be somewhat more costly to maintain.

The longer and heavier a coach is the more need there is for power. There is also the issue of carrying capability. So you will want to focus in on what size motorhome then look at the weight carrying abilities of your choices.

The modern Gasoline power trains and chassis have evolved tremendously in the past several years and the expectation that they will continue. If there is a Gasoline powered motorhome that meets your fancy it is worth a long hard look.

There are some benefits to going diesel powered other than fuel mileage ( which is not usually anything to write home about) A DP pusher will generally be quieter in the cockpit area when underway and will have the benefit of air suspension and Brakes.

Another minor benefit of a DP is that in many cases A DP will have a much longer range between fuel stops due to the size of the fuel tanks.

If you are looking at a length of the 35 or less then I would be looking at A Gasoline and over that you are in sort of a mixed bag up to about 38 feet then you really want to be leaning in the direction of a Diesel simply because of the torque to handle the weight.

You will need to sort out what you are looking for in terms of length and CCC plus the price range you are wanting to be at. A diesel will be a significant increase in price. Drive both and then figure out if the added cost is worth it to you.

So what does this all mean?

Some gasoline powered coaches will be challenged going up some steep or long grades but then so will some diesel powered coaches. The real question is so what? How much time will one spend going up steep grades?

There are aftermarket kits that can enhance performance such as the Banks System or the gear Vendors add on to the none Allison transmissions that adds extra gears. The Banks after market performance enhancements are available for both Gasoline and Diesel powered units. I have installed both in the past and still have a F350 4x4 that has both the Banks system and the Gear Vendors. The addition of a Banks or a competitive alternative will yield additional available power both in terms of Horsepower and Torque. The question of whether the additional cost of these systems will yield enough performance enhancement of warrant the cost.

In looking at the performance curves relative to the 8.1 on the Banks web site it should be noted that for an 8.1 the optimum gain is at a fairly high RPM which should be taken into account relative to cockpit noise. Using the most optimistic gain estimates you could be looking of 16 to 23% depending on rpm's in terms of torque. The RPM range will be between 3800 and 4800. The most material gain will be on acceleration especially on on ramps and passing.

In terms of pulling power up grades there will be improvement there as well. But lets compare getting 25,000 pounds up a grade with a banks enhanced gasoline 8.1 with getting 30,000 pounds up the grade with a Cat 330 powered diesel. Looking at the chart below the 8.1 with the Banks system will have to move 45 pounds for every foot pound of torque versus the Cat which will have to move 35 pounds for every foot pound even at the heavier weight. You can also see on the chart below that at the same weight the diesel will have even a greater advantage. However that is not the end of the story.

The W24 chassis comes with a 5.86 rear ratio which is nominally in the range of 20% higher than the typical rear ratio of a cat 330 equipped chassis so the 29 percent more weight per foot pound of torque available with the cat 330 is down to about a 9 percent difference in power to move the weight provided the gasoline unit is 5,000 pounds lighter. If the same weight then the cat will have about a 25% advantage in the ratio of weight to torque to move it even with the performance enhancement on the Gasoline engine. How much difference will this make to you? The only way to answer is to drive the same course with the two different power trains and see for your self.

Keep in mind that you will more than likely be testing a stock Gasoline engine and that adding a Banks or similar performance enhancing package will yield somewhere in the neighborhood of a 20 % improvement. What this means is that the performance enhancement kit will offset the weight that you are going down the road with towing a dinghy and with all your stuff on board. So if the performance suits you and you like the rest of the coach the Gasoline powered motorhome ought to be on your short list since it is possible to add the performance enhancement kit. The added expense of a performance enhancement kit will be far less that going the diesel route. The diesel as tested will be just about as good as it will be so keep in mind that the added wieght of towing a dinghy and carrying all your stuff may impact the performance you experienced during the test drive without the additional weight.




Torque.........455.. 560... ..660.....860.. 1050.. 1200

Weight
20,000......... 44... 36........30........23......19......17
25,000......... 55... 45........38........29......24......21
30,000......... 66... 54........45........35......29......25
35,000......... 77... 63........53........41......33......29
40,000......... 88... 71........61........47......38......33
Pounds to move per increment of torque

455 = Stock 8.1 Torque
560 = Banks equipped 8.1 Torque
660 = Cummins ISB 300 Torque
860 = Cat 330 Torque
1050 = Cummins ISC 350 Torque
1200 = Cummins ISL400 Torque

So the answer is yes these after market systems will help off set the power differential between a Gasoline Powered versus a Diesel Powered unit.The difference in actual performance getting that weight up the grade while not be as much as the chart would indicate since the Gasoline powered coach will have a higher rear end ratio and the higher revving gasoline engine to be able to take the advantage of the higher rear gearing.

One other issue to take into account with a normally aspirated engine (non turbo) is that the air density will have an impact on the power generated by the engine. "On a hot day, or at high altitude, or on a moist day, the air is less dense. A reduction in air density reduces the engine horsepower." Link So on those hot muggy days a non turbo engine will have less power than on a cool dry day. Adding altitude to the equation will also rob power on non turbo assisted engines. Virtually all modern diesels in today's motorhome will have a turbo as standard equipment. The power loss in most situations is not really significant. The loss is in the order of 1 % per thousand feet up to three thousand feet then about 3 % per thousand feet there after.

There is one advantage to a diesel worth considering and that is the auxiliary braking that is available via either an exhaust brake or an engine brake. To my way of thinking the availability of auxiliary braking is a far more important advantage than any extra power. Having said that, the perspective I have is that at times it is convenient and others it is a margin of safety that I really appreciate. The thing to keep in focus that it is possible to adjust ones driving pattern to proceed in a safe manner without the need or desire of an auxiliary brake.

A diesel powered coach with a power to weight ratio that is superior to a gasoline powered unit will be able to pull grades at a faster rate and descend down grades more aggressively if equipped with an auxiliary brake. An engine brake being superior to an exhaust brake. But again the question is so what? Just what percentage of the on the road time will be spent going up and down grades where this is really a material issue?

There are Gasoline coaches that will out perform some diesel coaches in terms of pulling grades. As I mentioned the longer and heavier a coach gets the more that the need of a diesel comes into play. In this case the word need is a euphemism for desirable. Feeding that desire does have a price tag. The issue is determining the need based on the size coach and then working through the coast versus the benefit.

The only way to know is to figure out what you want in terms of size and floor plan which will include the added weight of sliders. If you are a driver instead of a parker and you want a large coach then a diesel may be the better choice if you are a parker then it may make more sense to go with a Gasoline powered unit in terms of price.

Our needs were such that a 40 footer was our choice which got us into a Diesel. For our traveling partner a 32 footer Gasoline unit is the perfect size he is as happy with his choice as we are with ours. We have traveled together extensively in mountainous country in all but the steepest of grades he is able to maintain the same speed with his vortec 8.1 as we are with our ISL 400. While I think he would like to have a larger fuel tank and would benefit from an auxiliary brake he is as happy with his coach as were are with ours. Our ride may be a little smother due to the air ride and the cockpit noise level lower when climbing grades but to him those issues are not enough to justify the price differential of his coach versus ours.

With the innovations in chassis design of gasoline powered coaches and the addition of 5 and 6 speed transmissions given the price differential of going the diesel route I would look long and hard at the gasoline powered coaches. The only way to know is to pick your size and floor plan then do a test drive.

One thing that you will find is for the most part all of us like what we have but there is always something "better". I would discount those who disparage one type versus the other... Or makes extravagant claims not supported by any logic of the physics involved in moving weight. But I would pay attention to those that take the time to go beyond this is bad and that is good.

I also think that we at times get lost in generalities so I would suggest that you get in the ball park with generalities but focus on specifics when you are in decision mode.

In general 🙂 a diesel pusher will be quieter in the cockpit area, will offer a smooth ride due to air suspension. Some diesel pushers will offer pass through storage. Most diesel pushers will have some form of auxiliary braking either in terms of an exhaust or and engine brake. (Diesel Engine auxiliary Brakes)

In general :)At some price point the interior fit and finish of a Diesel Pusher will be a step up... But for the upper end of the Gasoline powered units and the entry level diesel and up to some point along the DP price curve I do not believe there is much if any difference.

In General 🙂 the more expensive DP's will offer additional amenities beyond what is available on Gasoline powered motorhomes.

In General 🙂 Diesel pushers will have a longer range due to larger fuel tanks.

Here is a thread The power equation...Horsepower- Torque -Gear Ratio- Weight for those that want to ponder on this issue further.

JohnnyT

[JetAonly]

bhildreth wrote:
Thanks for the replies above.
DP drivers sing praises (even gloat) about taking severe downhills without brakes using engine braking and downshifting. Does this mean no braking by their trailers? That sounds potentially dangerous especially in slick conditions.

Any trailer I pull will have its own brakes, for sure! My goal going down hill is to never touch the brakes, prudent use of exhaust/Jake brakes and down shifting allow this. The reason is cold brakes give you the most energy available for a stop as who knows when you might have to bring all 43K to a schreeeching halt. Hot brakes, as you know fade quickly, I've also seen them burning merrily down the hill with no stoping power left.

[mowermech]

All number crunching and science (and "pseudo-science") aside, when I wanted a little more room than our Tioga 29H Class C had, I looked at used DP units, and used gas units, and settled on a Southwind 32V single slide V10 powered Class A.
On our recent trip from Montana to Chattanooga and back, it performed flawlessly. We were towing the PT Cruiser on a dolly, and the hills and valleys presented no trouble at all.
I am no longer interested in a DP.

[bhildreth]

Thanks for the replies above.
DP drivers sing praises (even gloat) about taking severe downhills without brakes using engine braking and downshifting. Does this mean no braking by their trailers? That sounds potentially dangerous especially in slick conditions.

[JetAonly]

bhildreth wrote:
Great discussion. Thanks. I presently have medium TT towed by a Tundra. Did a 16,000 mi western states loop last summer and had 6 blow outs and actually broke a wheel hub. I'm 1000# less than gross. I'm thinking TT are just too lightly built for heavy traveling so I'm looking. As I travel with 6 bikes and probably a future inflatable kayak, I'll probably need to tow a trailer with small vehicle inside. I thought I wanted a diesel for towing ability uphill as well as engine braking downhill. Your discussion of gas has me interested however as I need only a 30-36 footer.
Finally my question, can gas rigs have brake abilities to tow a fairly heavy trailer?
Thanks.

I even uprated the axles and tires on my TT to stop this. Took me a while to figure this out. A load leveling hitch works both ways. What you load on the trailer goes to the truck and what you load on the truck get pushed to the trailer. FWIW

[427435]

bhildreth wrote:
Great discussion. Thanks. I presently have medium TT towed by a Tundra. Did a 16,000 mi western states loop last summer and had 6 blow outs and actually broke a wheel hub. I'm 1000# less than gross. I'm thinking TT are just too lightly built for heavy traveling so I'm looking. As I travel with 6 bikes and probably a future inflatable kayak, I'll probably need to tow a trailer with small vehicle inside. I thought I wanted a diesel for towing ability uphill as well as engine braking downhill. Your discussion of gas has me interested however as I need only a 30-36 footer.
Finally my question, can gas rigs have brake abilities to tow a fairly heavy trailer?
Thanks.

To answer your actual question about trailer brakes, a "fairly heavy" trailer should have its own brakes-----------whether it is being towed by a gas or diesel powered MH.

Most newer gas MH's are rated to pull 5000 lbs while the diesel's are usually rated for more (not always). Most gas MH's say that anything towed over 1500 lbs should have its own brakes. While many diesel MH owners will tow fairly heavy stuff without brakes, I don't know what their owner's manual actually says.

[Cloud_Dancer]

nostrings65 wrote:
...and then there is the bottom line...men who drive pushers think its the ONLY way to go and feel superior to those of us in the gas class A category....8 years fulltiming and I've seen it and heard about it more than I would care to....gotta have that torque and room enough for the wife's crap. Just sayin.

You're the only one I've ever heard of who had a problem with this. I'll have to be more careful next time..........

[BillMFl]

Lets grant that the DP rides smoother and can tow more. It may get a few more mpg but diesel fuel costs at least 10% more per gallon which negates any advantage there. A fully equiped 38' gasser will cost about half what a 38' DP costs. The newer DPs will typically have ceramic tile and granite counter tops, and usually better quality all wood cabinets, generally nicer interiors because of the higher weight carrying capacity. My gasser has big slides, king size bed, double sink vanity, onan gen, auto awning, big double frig, w/d hook ups, a second half bath, 3 flat screen tvs, surround sound system, lots of hanging closet space, lots of dresser drawers and lovely full body paint and fiber glass roof, side and rear cameras and roomy kitchen with plenty of storage and counter top space. In short, it is a very comfortable spacious floor plan with all the creature comforts of home. Is a smoother quieter ride, more hp for the mountains out west and a little more snob appeal worth almost double the price (if buying brand new)? Not for me. I have the tile and granite and large swimming pool at home. I spend only a few months of the year on the road. I paid cash for my 2012 coach, and could have done the samefor a DP, so cost was not the primary consideration. What it boils down to is how much are you going to use your unit, and how much will you loose in depreciation a few years down the road. These thing do not appreciate in value like real estate does. Whatever you buy, it will be worth substantially less when you decide to sell or trade it. Just like a car, the choice depends on how big and fancy you need to satisfy your personnal wants and needs. There also is a huge difference between a full timer vs the average rv owner who uses his unit 6 to 8000 miles and a few weeks per year. No one choice is perfect for all. And there will always be those who will need a million dollar plus Prevost for their infrequent trips to a Nascar race, etc. For me the choice of a fully equiped 38' gasser that cost about half that of a fully equiped DP was an easy one. But then I like my Ford Fusion hybrid just fine, while some of my buddies have to have BMW's etc. As a retired engineer I still do a cost/effectiveness analysis on every big ticket item I buy. Except for my 43' twin diesel Trawler, which has absolutely no justification other than the fun of using it. Its a big hole in the water that I pour way more money into than a 43' DP would cost. You pick your toys and you pays you money!!! My wife says thank god he doesn't like to fly. 🙂

[bhildreth]

Great discussion. Thanks. I presently have medium TT towed by a Tundra. Did a 16,000 mi western states loop last summer and had 6 blow outs and actually broke a wheel hub. I'm 1000# less than gross. I'm thinking TT are just too lightly built for heavy traveling so I'm looking. As I travel with 6 bikes and probably a future inflatable kayak, I'll probably need to tow a trailer with small vehicle inside. I thought I wanted a diesel for towing ability uphill as well as engine braking downhill. Your discussion of gas has me interested however as I need only a 30-36 footer.
Finally my question, can gas rigs have brake abilities to tow a fairly heavy trailer?
Thanks.

[jdubya]

I now have a 2004 Fleetwood Flair 33R with a gasoline engine (8.1 Chevy Vortec). I do not find it to be too noisy nor emasculating to drive. I really like the sound of a V8, and it is not underpowered any more than my 1993 Itasca Suncruiser with a B-series Cummins.

1. Gasoline engines use more fuel about 10% (7 mpg gasoline vs 8 mpg diesel) for approximately the same size vehicle. (10% more fuel that has 10% less BTU available at 10% less cost - I call that a wash.)

2. Just because you are paying for a diesel does not mean you are buying airbags rather than springs - both of mine had springs.

3. I prefer diesel pushers because they seem to be built better, but they cost so much more. (We really liked our no-slide Itasca diesel, but we also really like the two-slide Fleetwood - both are really cool to drive, but are much more white-knuckle to drive than our 2500 Dodge 4x4 with the big fifth wheel behind it. We found that the fifth wheels that we had were generally speaking pretty junky by comparison to the motor homes. We had a Cedar Creek 37RQLS which was poor though much better than a piece-of-junk Open Range 337RLS which was shameful display of poor quality - despite what some owners have conned themselves into thinking. I might change my tune if the frame rails on a motorhome fail as the Open Range did. I think that OR has improved, but the early ones were nothing to write home about.)

[driveby]

1rocko wrote:
I have noticed that they have different hp ratings for the ford triton v-10 305 hp for class c motorhomes and 365 hp for class A motorhomes typo error I asked a local ford dealer they said they were unawared of 2 hp ratings for the v-10 I am thinking of trading my class c on a class A gas would like your thoughts on this

There are. 2 valve in e series because of no room under hood. Air breathing I think. Class a has 3 valve. This was true in 2007. Not sure it its changed since.

[randco]

When we started our process to purchase we knew we wanted something in the 38' range. We liked floor plans of some of the gassers but the wife really like the floor plans of the DP's.

We had the opportunity to test drive two coaches manufactured around 2005. One was a Class A on a Workhorse chassis and the other a DP. We drove the Class A first. The Class A was a very nice Winnebago. It had moderate acceptable engine noise and a the ride was pretty darn good. The braking was more than adequate. All in all, it was a pleasurable driving experience.

When we got back to the dealership a 40' DP with a Freightliner/Cat combination was ready for us to test drive. Almost immediately we both knew there was no comparison. Virtually no engine noise and the ride was very very smooth. Getting used to the air brakes was a little different in the beginning. After the test drives we knew that a DP was in our future.

Bottom line, find the floor plan you like. Then test drive and compare vehicles. It's your money, you know what you can afford.

[Jarlaxle]

The vans (and class C's) have the 2-valve V10...class A's (and pickup trucks) use the 3-valve V10. The 3-valve won;t fit the vans.

[1rocko]

I have noticed that they have different hp ratings for the ford triton v-10 305 hp for class c motorhomes and 365 hp for class A motorhomes typo error I asked a local ford dealer they said they were unawared of 2 hp ratings for the v-10 I am thinking of trading my class c on a class A gas would like your thoughts on this

[mena661]

The Ford V10 is a 6.8L. GM is 8.1L V8. Both make similar power and torque at the same rpm ranges. Both engines will serve you well. The GM one is no longer produced but that shouldn't be a big deal. Tell your DH that the majority of gas motorhomes have Ford's engine in them. The V10 is a great engine.

[Sully2]

zep wrote:
I think I finally have hubby convinced that we won't live long enough to benefit from the extra cost or the 'if' better fuel mileage of a diesel. That said, reading this article is very interesting because I kept reading 'GM 8.1' which would be husbands choice over Ford. What is the difference between the Ford 6.3 and the Chevy 8.1?? which delivers better torque, horsepower and fuel mileage assuming units are identical?

I'm having a difficult picking out a 'used' unit, 2007 or new because so many are the Fords and I can't get the husband past this part.

Any help will be greatly appreciated.

PS: We currently pull a tt but it's a lot of work for him retiring in a year or so.

Give the guy a break for once....Get a DP so he can have fun too. Where's it written that one needs to get better milage or any sort of benifit in owning a diesel over a gasser???