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

[mrlightrail]

What about the Chevy 454? Solid engine, in a LOT of 90's RV's, but I want to avoid carb engines, and would rather go for fuel injection to max out the mileage you can squeeze from these big motors.

[mrlightrail]

That reminds me of when I took our family on vacation in our Audi 5000. Got into the Rockies, and the best I could get out of that car at higher altitudes was about 30 mph. I was getting passed by VW beetles!!!! Once we got lower, my performance returned.

[Peralko]

One issue I haven't seen mentioned in the gas vs. diesel is the fact that diesels are turbocharged, gas engines are not. This makes a huge difference when you get up into altitude. I still remember going up a not particularly steep hill in our old Pace Arrow, and all I could bet out of it was 35 MPH. With our DP, I have not noticed any significant power loss at or above 10,000 feet.
Durability is another issue. Our 454 Chevy engine warped an exhaust manifold at about 80,000 miles, and needed a valve job at the same time. With about 155,000 miles on our DP, the Cat is purring along quite nicely.
There is no way I would go back to a gasser. There are too many older DPs that can be bought very reasonably.

[mrlightrail]

jdubya, You hit the nail on the head on my concerns about earlier model gassers. I would be very careful if an engine swap had occurred in a coach I was looking at due to the slight, but important differences between truck and car engines.

Remember the fiasco when GMC created the car diesel from a 350cid gasser block? I also remember the early gen front wheel drive cars (Toronado) with high failure rates. I love the 73-78 GMC "bullet" chassis, with the dual axle rear, but, it is front wheel drive, plus the carbureted 454, which means low fuel mileage, and questionable reliability. (Might buy one anyway, as a project, or local lake runner.)

I drove buses for Trailways,Greyhound,and a couple of regionals before leaving the workforcs, so I know busses pretty well. Diesel maintenance does not scare me, and honestly, I think the costs of maintenance if done by the owner will be a wash due to maintenance frequency differences. (Also, I got a son-in-law who is a diesel mechanic for the oil patch.)

I know the reliability factor for converted Greyhounds is big, as those coaches were designed to be million-milers. Consumer grade dp's, I don't know.

Most of the RV's I'm looking at have the 460 Ford, or the 454 Chevy. If I see a carburetor, I run. TBI? I am nervous, fuel injected, I will consider it.

Remember, I have a HARD cap of 15,000 for buying the RV. So, 88-98 is the sweet spot for my price range from what I've seen so for. This will mean no extended warranty for my rig, as Good Sam won't cover anything older than a 99.

I've spent whole nights reading the forums, bouncing around hither and yon, and the diesel/gasser debate rages strongly. I'm not rich, don't plan on being wealthy, and therefore, won't be trading up every few years. Whatever I get will be mine for 5-10 years before replacement.

That's why I am looking very hard at the two diesel pushers in my price range. Both are by Beaver, which I have never heard about. decent floor plans, and both use the Cat 250hp engines. Now, I've also seen GMC 4104 conversions coming close to my budget lately, with the 4 speed crash box, and the Detroit diesel.

The ONLY reason I still look at gassers, is price. If I find a well maintained gasser for significantly less than 15k, I may go there, otherwise, I will keep looking for diesel, or start to give fivers a harder look.

The selling point for the fiver/TT is my tow vehicle is my toad, and I'm not stranded at the park. My Pinto Wagon is not a good candidate for a toad, so I have to figure in the cost of a towable in my price figures.

Keep the comments flowing. I AM reading them, and researching. As I am a VERY outgoing person, I may hit a few campgrounds, and hit some folks up on their choices, too. Nothing better than a face to face talk to impart knowledge, in my book. 🙂

[jdubya]

solidfiction: You make my point - there is a real difference in how the two are designed. The engines in trucks ran for a long time, the engines in the cars ran for a long time, but if a car engine was put into a truck, bad news. The bus had a lot of miles on it. The engine blew and they bought one from a junk yard, it blew, so they got another - it blew so they bought a reman. When it blew shortly after the warranty was up - no more bucks for that bus. (Not sure there might have been one more.) BTW I am fairly certain that all of the engines were car engines rebuilt with the same claim that they were equivalent to the truck engine they replaced.

I am not an expert, though I have worked on a lot of engines, and I was not directly involved in finding out what was wrong with those 460s, nor what failed, but I do know that the engines went out one after the other with very few service miles on each of them - that is not the mark of a 'good' engine.

The people who did the work were very reputable people, too. And the experiences of many Chevy and Ford engine owners who had these engines in RVs attest to the truth of the 'perception' that those old gassers were nothing to write home about. 'Buy one at your peril' is my thought - maybe you'll get lucky and it will run for a long time, maybe not. My advice remains 'buy a later model with a V10 or Vortec'.

The same problem could happen with the later engines, too. But the experience is that the manufacturers have done something to make them more 'reliable'. I have not studied the subject to find out what.

[solidfiction]

Jdubya wrote:The 'good' 460s were for trucks, not cars, but they were treated interchangeably though they weren't interchangeable. I know because we dealt with that at an institution I was involved with - engine after engine burned up in our bus until we just gave up on it. They were all 460s. I am pretty sure they were putting car 460s in the bus and they couldn't stand the load.

I owned a engine reman shop and I can tell u this is not really all 100%true.I certainly would not dispute you had engine problems in this bus as there are some parts and pieces such as valves and camshafts that have different specs etc but neither have anything to do with a "burn up".There were probable extenuating circumstances causing your failures that got missed or overlooked

[jdubya]

I really didn't intend to get into the old discussion about older engines - yes, it is possible to get the older engines to work well, but they were notorious. So my take is to stay away from them. Besides, it is getting harder to get parts for them, while the V10 are more available and are well known to be reliable. My point to the mrlightrail was to stay away from older ones for those reasons, not because you couldn't find a good one. Most people wouldn't know a good engine from a not so good one - they only know they were 460 cu inch and assume it is a good engine - that is not so. The 'good' 460s were for trucks, not cars, but they were treated interchangeably though they weren't interchangeable. I know because we dealt with that at an institution I was involved with - engine after engine burned up in our bus until we just gave up on it. They were all 460s. I am pretty sure they were putting car 460s in the bus and they couldn't stand the load.

About diesel mileage - the old diesels, B series Cummins for example, do not get as good mileage as the newer IS series. I have had the Cummins B w/275 hp, I think, and it averaged 8 mpg or so. The newer ISB Cummins I had in my Dodge 2500 was better and would get 11.5 - 12 most of the time towing a 39' or a 34' 5er. I kept mileage religiously on it. But it depends a lot on how you drive; speed and taking advantage of the lay of the road, not racing up hill etc etc. I have nursed as high as 13.5 and had as low as 8 on that PU though towing both the 39' Cedar Creek and a 34' Open Range. (Got the highest mileage towing the Cedar Creek, BTW). That PU would get over 20 mpg when not towing. So I would recommend to mrlightrail that he get an engine of that age range - the systems and design are better than in the old ones, parts are readily available and they are very reliable.

Gassers on the other hand have not been reliable until the age of the V10 and the Chevy Vortec. Individual experience will vary, but I am unwilling to risk it. Just be forewarned.

About ownership costs - I think in the long run I would go with a diesel pusher if I possibly could swing it. I happened to find a gasser that has the engine cover almost flat on the floor which to me was a big plus. It is a 2004 Fleetwood Flair 33R. We have done very little traveling with it. I bought it with 19000 miles on it last spring. It runs real well, but the mileage is atrocious at 7 mpg as expected. But compared to the 1993 Itasca dp it did very well (the Itasca had no slides 35') - but the price of fuel is a killer.

Anyway the point I was going to make is that the trip to Salt Lake City is a breeze for the diesel and it will get its best mileage. Throw in some mountains and the gasser will still get 7 mpg average while the diesel will drop down to 8 or so average. That is my experience anyway. (I still prefer the diesel pusher if you feel you will get enough use to make it worthwhile to have the expense of getting the best. The best just isn't that much better to make it ideal for an occasional user - that's all). And individual situations and experiences will vary.

Update: I erred in stating 'OP' - it should have been 'mrlightrail' I edited it in at least two places and can't find any others, so make the correction if you see more.

[solidfiction]

royl wrote:

mchero wrote:
Posted this on my dieselrvowners forum;

Different way of looking at it.

Was looking at the cost of a trip from New Hampshire to Salt Lake City UT. I used the going price of diesel & gas here in Concord NH. Interesting;

RT Concord NH to Salt Lake City UT

Miles--Driven----MPG----Price/Gal---Total Cost
Gas----4693-------7--------2.1-----------$1,407.90
Diesel-4693------11--------2.45---------$1,045.26

Great Post JonnyT

True but then figure in the cost of buying the diesel over buying the gasser and it would take many more miles than the average rver will drive to make the diesel cheaper to own. Then figure in the increased cost of maintaining the diesel and you will never make the diesel cheaper to drive. It boils down to preference and your budget.

OK except now show me what model diesel pusher gets 11MPG???
when i talk Class A DP I mean 3-4 slides 40+ feet and 400+HP
VERY VERY few if any diesel motor homes of any make or model loaded up no matter will never get 11 MPG average

[royl]

If you know how to drive in the mountains you will have no problems with a gasser without an exhaust brake. Just do not get in a hurry,(why would we be in a hurry anyway), start the downhill slope slowly, use the tranny lower gears to keep your speed down, do not ride the brakes, apply them as needed to slow down and then get your foot off them to allow them to cool, make sure you have a braking system on your toad or trailer. I have never had hot brake problems.
Don't let anyone tell you the older engines can't hold up. The 460 Ford if equipped with headers and a quality exhaust system is a workhorse that will give you years of dependable service.

[royl]

mchero wrote:
Posted this on my dieselrvowners forum;

Different way of looking at it.

Was looking at the cost of a trip from New Hampshire to Salt Lake City UT. I used the going price of diesel & gas here in Concord NH. Interesting;

RT Concord NH to Salt Lake City UT

Miles--Driven----MPG----Price/Gal---Total Cost
Gas----4693-------7--------2.1-----------$1,407.90
Diesel-4693------11--------2.45---------$1,045.26

Great Post JonnyT

True but then figure in the cost of buying the diesel over buying the gasser and it would take many more miles than the average rver will drive to make the diesel cheaper to own. Then figure in the increased cost of maintaining the diesel and you will never make the diesel cheaper to drive. It boils down to preference and your budget.

[bruce2]

Thanks to mrlightrail to getting this discussion down toward my financial level. I did a 16k mile western states loop last summer and my lightweight travel trailer was not up to the task. So looking for an older class A. I have maybe up to $50-60k to spend. We spend most of our time in USFS type campgrounds and I want to limit size to 34ft or less. I'm aware of comments on this site that I should look at big gassers in this size range. I spend a lot of time in mountains and warped my brake discs last year on a long, steep downhill. So, I'd love engine braking.
jdubya hit the hot-button with his comments about what improvements were made to gassers and DPs from the mid 90's to the mid 2000's to see if it is worth the jump. Please expand on that idea. TVs I can change myself. What about drive train and suspension issues, maintenance, etc. Thanks

[jdubya]

Your call - sounds like a plan.

I might add that had I not cheaped out on our first one, we might still have it and not have gone through the trials of 5ers (although our first 5er was a 39' Cedar Creek which had some problems with cheapo drawers and other relatively easy to fix stuff, it was pretty good though too long). I And the cost involved in trading every few years would have easily paid for the extra cost of a good diesel pusher with slides. But we would also be missing some of the improvements that they have put on later models like HD and LCD TVs, slideout covers, auto levelers, etc not to mention the improved systems on other parts of the motorhome.


Good luck!

[mrlightrail]

I'm kinda leaning towards finding something without slides. Firstly, folks like you are dumping them in favor of slides, which makes me get better deals on something I could otherwise not afford. Eventually, I'd like one, but I can wait. I have 15k to play with on the purchase. the gassers are all low to mid 90's, and the two diesels are a 91 and a 93. One with 60k the other with 110k miles. Both are Beavers, and are selling cheap, compared to others I've seen sold.

[jdubya]

We had a 1993 Itasca Suncruiser diesel pusher from about 2000 to 2003 and we really liked it except it had no slideouts. We only got rid of it when we were fulltiming for a year while our house was being built. For just the two of us it was fine but living in it fulltime was more than DW could stand. So she found a fifth wheel that she liked and we traded for it without even owning a pickup to pull it with!

Anyway if you can possible swing it, the diesel is by far the best deal in the older ones. Consider going to a gasser that is much newer with slides and at least a Chevy Vortec or Ford V10 - don't even bother with those older engines, in general, the engines can't take the load.

We are back in a 2004 Chevy Vortec motorhome with 20K miles and 2 slides 33 ft long which is a great size. But it set us back $47K. It has lots of nice features and is easy to drive. We tow a 2009 Jeep Liberty 4x4 behind it and get about 7 mpg average compared to 8-9 for the 93 Cummins B series diesel which is about a wash cost per mile but I liked the diesel pusher better.

If you are not up to handling a lot of repairs yourself, one repair bill will probably kill your budget especially on the diesel. And parts are much harder to find.

[mrlightrail]

I'm about ready to pull the trigger for a Class A, and I'm looking at the model years 88-95. Pace Arrows,Early 90's Beaver Contessa's (dp) so far...The gassers in the bunch are around 5-8k, while the diesels are 9-15k in price. Most of the discussions here are for MUCH newer RV's, WAY out of my price range, so I'd like to hear from folks who have owned older models to see how they match up.