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

[Dog_Trainer]

I don't believe that the ISB is in MH with less than 605 Ft Lbs torque My 93 B5.9 is rated at 605 Ft lbs. which is about 33% more torque than the 8.1 GM

[Triker33]

I also think that CCC is important if you want to put after market things on such as solar panels, antennas, mother-in-law, etc.

Now you are saying the benefit if you get a gas model, with less CCC. You may have to tell your mother-in-law, she can't come along because you are out of CCC. 🙂

Now you have just gone and loss some DP sells. :B

[jwillie44]

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.


Diesels also have larger fresh water and waste holding tanks. An important consideration for boondockers.

I also think that CCC is important if you want to put after market things on such as solar panels, antennas, mother-in-law, etc.

Golfers, and others with certain hobbies, will appreciate the pass through storage under some coaches.

[dalemaxx12]

I want to thank everyone for their responses and the great information. I think this site is really great. Thanks again,
Dale

[driveby]

This is a great post. I think the biggest challenge is doing a like for like comparison. Either you have a new DP and your old gasser was pre improved (IE 2001 or older) so that isn't fair. Or you're comparing an air ride vs spring ride chassis. I think the fairest comparison for engine choices is the FRED vs Workhorse or FRED vs F53. I think Tiffin is one of the few if any that offers the same floorplan on both. That to me would be the litmus test. Anything else has too many variables - IE I can't buy my floorplan choice from Winnie on anything but a gas chassis. nor can I buy a 42'+ gas chassis.

[MeanderMan]

I always enjoy Johnny's posts; articulate, informative, and thought-provoking. As a full-timer and former owner of a newer gas MH (06 37' Tiffin Allegro Bay), and current owner of a DP (40'06 Itasca Ellipse), I'd like to share my experiences.

We full timed in our Allegro Bay for three years, mostly throughout the west. Mountains were never a problem, gas mileage averaged 7MPG, and it was (except for routine maintenance) completely trouble free.

With our DP, we've had some minor maintenance issues, and average 8 MPG.
The differences:
- The DP certainly rides and drives better, but not significantly until there's a crosswind or headwind, and then the higher weight and stability kick in. I find that I'm less fatigued after a day driving the DP than I was with the gasser.
- The DP is quieter, but again not significant unless climbing a hill; the Workhorse would scream pretty well when in 2nd & 3rd gear, but was very quiet otherwise.
- The big disk brakes on the Allegro Bay gave a better sense of braking, but the exhaust brake on the DP is great also.
- Maintenance is a significant factor. As a full timer, I don't have a garage/workshop, the places we stay don't normally allow maintenance to be performed, and besides, I'm retired & would rather not do the work. With the Workhorse, it was like a big pickup truck; easy to access, easy to work on. Durability and long-term warranty were excellent. Same transmission as the DP. Oil changes, even with synthetic oil, were reasonable (less than $100). Almost any mechanic could work in it.
With the DP (and rear radiator), it can take 30 minutes of floor panel and engine cover removal just to SEE the engine. Fluids are greater in quantity and more expensive, there are more filters (both air and fluid), and engine-specific maintenance (while available in urban areas and along interstate highways) is more difficult to find. This year the coach is due for 20K mile service; I expect it to cost between $800-1200, and this is the low end because I'm taking it to the plant.

So is the difference in cost worth it? Yes, to me, because I'm a full timer and wanted more room (4 slides), more CCC, and a more stable ride. Did I need to buy a DP? Not really, the Allegro Bay was a great coach and certainly served us well. Personally, I'd never recommend a large DP to someone who only used it for vacations; it's too large an investment in initial cost and annual maintenance to justify the purchase. Today's higher-end gas MHs offer the amenities and performance that a few years ago belonged to the better DPs. As always, it's a personal choice, but that choice is always easier when you can learn from others.

It's all good in the RV lifestyle, no matter what you own!
Keith

[SunflyerA]

dalemaxx12 wrote:
This is my first post, so here goes. I am considering a used Class A motor home and have found 2 that I really like. One is a 330 Cummins diesel pusher and the other is a v10 gas. Both units are 38'.

I am curious about the difference I can expect when climbing the mountains going south on I-75 from the Ohio River into Kentucky. Will the gas MH be able to keep up with traffic going up the steep grade pulling a tow vehicle or will the DP be the better choice for me?

I have a preference to the gas MH floor plan but the DP is really nice too. If I choose the gas model, I don't want to be creeping along the road every time I come to an incline of a substantial distance.

Any help would be appreciated!

Thank you,
Dale

I took my fully loaded Sunflyer V10(20,500)pulling a 5000lb toad up the Rockies....I found it to be completely acceptable. I was moving slow on some of the grades, but like someone here said; how often are you doing that. I also put some after market items on my rig that made it ride and track as well as my current Dp...it actually handled the wind a little better.

You need to consider how you are going to use your rig. Johnny T said the diesel rides quieter in the cockpit (it does) but if one of you wanted to sleep on the bed while under way; well, there is nothing quiet about the bedroom...

The V10 was loud up front but I never did try to quiet it with insulation...might be possible. CCC is the reason I moved to the diesel but with some of the newer Gas chassis I would certainly consider them if I was looking again....I think the cost of operation is somewhat cheaper on a gasser....I did not experience any increase in mileage from a diesel...about a 1/2 mpg less.

[Sully2]

427435 wrote:

dalemaxx12 wrote:
This is my first post, so here goes. I am considering a used Class A motor home and have found 2 that I really like. One is a 330 Cummins diesel pusher and the other is a v10 gas. Both units are 38'.

I am curious about the difference I can expect when climbing the mountains going south on I-75 from the Ohio River into Kentucky. Will the gas MH be able to keep up with traffic going up the steep grade pulling a tow vehicle or will the DP be the better choice for me?

I have a preference to the gas MH floor plan but the DP is really nice too. If I choose the gas model, I don't want to be creeping along the road every time I come to an incline of a substantial distance.

Any help would be appreciated!

Thank you,
Dale

The V10 will keep up with a 330 hp DP on the roads you asked about. You will need to run it at 4000-4500 rpm, however, to climb those hills well. The V10 will be cheaper to maintain if you're not driving more than 5,000-7000 miles/year.....

I agree and also disagree! If the DP is as heavy as my 36 footer is...and the gasser weighs in at 15L ( scaled weight) it most probably will do just fine. If the V10 on the Ford chassis is loaded down for a vacation and weighing 24-25K ( actual..physical weight)..basically no way in H*** Even at 4500 rpm there isnt enough TORQUE to maintain the forward momentum.

Flat ground running..no problem there ( we are talking ONLY about speed and acceleration here now)

Also Im talking about BARE COACH. Hook a 4000 plus toad in behind..and you'll be topping the "cut in the hill" at a screaming 35-40 MPH

[texasbaskets]

Only JohnnyT has the tact to start a diesel vs. gas post. 🙂 Nice work.

Only a few years back there weren't any heavy capacity gas chassis. When we were looking at A's in '03 and '04, the 22k chassis was just hitting the scene and was an 8,000$ option. Slideouts were getting more popular and they often ate up any CCC you gained. Besides that, the cost was now approaching the price of a basic DP. We wanted more sq. foot so we had to go diesel to get it. That said, I'm a DP owner who would now look at a gas chassis the next time around. That's because the sq. foot on a shorter 4 slide rig is about the same and there is actually some CCC. 🙂

[427435]

dalemaxx12 wrote:
This is my first post, so here goes. I am considering a used Class A motor home and have found 2 that I really like. One is a 330 Cummins diesel pusher and the other is a v10 gas. Both units are 38'.

I am curious about the difference I can expect when climbing the mountains going south on I-75 from the Ohio River into Kentucky. Will the gas MH be able to keep up with traffic going up the steep grade pulling a tow vehicle or will the DP be the better choice for me?

I have a preference to the gas MH floor plan but the DP is really nice too. If I choose the gas model, I don't want to be creeping along the road every time I come to an incline of a substantial distance.

Any help would be appreciated!

Thank you,
Dale

The V10 will keep up with a 330 hp DP on the roads you asked about. You will need to run it at 4000-4500 rpm, however, to climb those hills well. The V10 will be cheaper to maintain if you're not driving more than 5,000-7000 miles/year.

Drive them both and evaluate the handling and cabin noise yourself. The Ford F53 chassis may handle OK and be acceptably quiet or it may need alignment, better shocks, and sound insulation added to the dog house (none of which is hard or expensive to do). It's your money so choose wisely.

[mike_brez]

I'm not even going to consider a gasser next time around. You cant compare a DP ride and brakes to gas.

[dalemaxx12]

This is my first post, so here goes. I am considering a used Class A motor home and have found 2 that I really like. One is a 330 Cummins diesel pusher and the other is a v10 gas. Both units are 38'.

I am curious about the difference I can expect when climbing the mountains going south on I-75 from the Ohio River into Kentucky. Will the gas MH be able to keep up with traffic going up the steep grade pulling a tow vehicle or will the DP be the better choice for me?

I have a preference to the gas MH floor plan but the DP is really nice too. If I choose the gas model, I don't want to be creeping along the road every time I come to an incline of a substantial distance.

Any help would be appreciated!

Thank you,
Dale

[B_Bob]

I have an old gas motorhome with 172,000 miles on it. A 1975 GMC. I have been thinking a little bit about upgrading to a newer little bit more luxurious motorhome. My coaches first motor went 126,000 miles. And the second one is running fine. My point. I read a lot and in this thread that diesel motors last longer than gas ones. My comment would be that, that is a theoretical possibility. But not necessarily what happens in normal motorhome usage.

Many of the older diesel motorhomes I have been looking at have to have a new motor at less than what my GMC got on it's Oldsmobile V8 gaser. I have been looking at older Bluebirds and most of them that get to 126,000 miles have had a new motor put in or their original one rebuilt.

Absolutely no question that a huge advantage of a diesel is the much higher torque. But you pay a lot to get that. Most people justify it by saying the diesel lasts longer, maybe that is true.

BTW - my CPA has a 1982 turbo Benz diesel with over 900,000 miles on it. Motor has not been rebuilt. What he does though is drive his car every day. IMHO most motorhome diesels give up early because the sit around not being used regularly.

[Smitty77]

UFO adds another option that was unknown when this great thread was started.

Falls again into the over 36', but under 40' range. 8.1 power and Allison 6spd trans combo.

Toss in the Brazel (sp?) mod, and perhaps the Banks (if available for UFO?) - and this does add another option to the mix.

Quality of units between DP and Gas was pointed out, with the medium to high end DP's having options not available to gas...

The DW and I continue our research, and may pull they purchase date in a year or two earlier then expected, to take advantage of this unusual 'buyer's' market.

We'll keep looking hard at the UFO's, and gently used higher end DP's. Enjoying the research, and learning every day!!

UFO thoughts from others?

Best to all, be safe,
Smitty

[2micro4u]

Thanks for clarifying this to me.