Gas/Diesel considerations

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MikeFromMesa

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My wife and I have been camping in an older Class B (2005 Pleasure-Way) and are in the process of trading it in for a new (or newer) RV, but this time something bigger. We have been looking at B+ and C class RVs and found several that we are pleased with, and I am trying to understand the advantages and disadvantages of gas and diesel engines.

I have little experience with diesel engines except for the time many, many years ago when I was in the military and drove some diesel trucks, but know nothing about the current diesel engine technology. Back then diesels had the reputation of being more durable than gasoline engines, but being difficult to start in cold weather, being noisy and polluting with a bad smelling exhaust, but I assume much of that has probably changed. Perhaps someone can help me by answering some basic questions - do diesels get better fuel economy than gas, given the same driving conditions? Is it more difficult to find diesel repair facilities in small towns in the US than for gasoline? Are diesels as responsive as gas engines? Given the improved technology for gas engines they now routinely exceed 100,000 miles so are diesels any more durable than gas?

We live in the southwest US where the summers are pretty hot (with temperatures often over 110 F), so are diesels as good as gas in hot weather? In cold weather (we do travel out of Arizona, especially in the summer). I would appreciate any help I can get in trying to determine if we want a gas or diesel RV. Thank you for any help you can provide.
 

lynnmor

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Diesel engines today are very civilized, the real reason to buy one is much better fuel efficiency.
 

Great Horned Owl

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Diesels have even more advantages than they used to. They still last longer. and they do get better fuel economy. They have a lot more torque, so they are better going up hills. They are turbo charged, so they accelerate better than they used to. Stomp on th pedal. and there is a fraction of a second delay while the turbo spins up. It was a little disconcerting at first, but I no longer even notice it

Diesels now have glow plugs, so cold weather starting is no longer an issue. I have had no trouble starting mine in sub-zero temperatures. They have new pollution control systems, so they are as clean as, or cleaner than gas engines. I don't have a very good nose, but I don't smell anything. The one down side is the need to add DEF (diesel exhaust fluid) every few thousand miles.

Small towns are usually either in farming or ranching country, so diesels are quite common, If anything, is is in the cities where diesels are less common. Many big city gas stations don't carry diesel fuel.

there are a few negatives. Maintenance, even routine oil changes, will be more expensive. If you ever run out of fuel, starting will be difficult. You will need to prime the filter. The biggest negative, is the initial cost of the diesel.

Joel
 

Gizmo

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Diesel engines do typically get better fuel mileage, though I doubt the savings realized at the pump cover the added expense of the higher purchase cost of a diesel and the higher maintenance costs.  IMHO, the choice whether to buy a diesel or not comes down, is it the right tool for the job.  The advantages of diesels are more towing capability, higher payload capability and full power delivery in the mountains (higher altitudes) to name a few.  If you are considering a larger motor home and particularly if you plan to tow a heavy vehicle or heavy trailer a diesel may be in your best interest.  On the other hand if on the other side of the equation and if you do not mind slower travel up steep mountain passes, a gasser may serve you just fine.
 

MikeFromMesa

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Great Horned Owl said:
Diesels have even more advantages than they used to. They still last longer. and they do get better fuel economy. They have a lot more torque, so they are better going up hills. They are turbo charged, so they accelerate better than they used to. Stomp on th pedal. and there is a fraction of a second delay while the turbo spins up. It was a little disconcerting at first, but I no longer even notice it

Diesels now have glow plugs, so cold weather starting is no longer an issue. I have had no trouble starting mine in sub-zero temperatures. They have new pollution control systems, so they are as clean as, or cleaner than gas engines. I don't have a very good nose, but I don't smell anything. The one down side is the need to add DEF (diesel exhaust fluid) every few thousand miles.

Small towns are usually either in farming or ranching country, so diesels are quite common, If anything, is is in the cities where diesels are less common. Many big city gas stations don't carry diesel fuel.

there are a few negatives. Maintenance, even routine oil changes, will be more expensive. If you ever run out of fuel, starting will be difficult. You will need to prime the filter. The biggest negative, is the initial cost of the diesel.

Joel

Thank you for your very complete response.

I was wondering about fuel economy because years ago I owned a small gas Class A motorhome and it gave me about 8-9 mpg, and people I knew who had diesel Class A motorhomes were getting about 4-6 mpg. Of course they had 35-40 ft RVs while mine was only 29 ft, but the fact that the diesel RVs were getting worse mileage than my gas RV made me wonder. I know it all depends on how you drive, and perhaps I was being much more careful and moderate in my stops and starts, but it still made me wonder.

I am surprised to hear that diesels have more torque and are better when climbing hills, but I am probably still mired in what I used to know about diesels 50 years ago and I am sure that is no longer valid. You mentioned DEF and the need to add it every few thousand miles. I assume that is an additive to the fuel, but why do they not include that in the diesel fuel itself? I have seen it for sale in some of the truck stops where I fuel up with gas, but had no idea what it actually was.

As for the price, I have seen that in our shopping. Diesels seem to add about $15,000-$20,000 to the price of the RV. I have seen 2 diesels as common - Mercedes and Ford. Is there a significant difference in quality?

Thanks again for your quick and complete response.
 

Roy M

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Diesels develop their torque at a much lower rpm than gas, my Cummins 5.9 is happiest around 1700 which is a fast idle for a gasser, and no way said gasser can match it for fuel economy towing. Maintenance is more expensive but less frequent so that's a wash. The new diesels are very quiet and properly maintained don't stink. The downside is initial cost, you will need to drive a lot of miles to recoup the difference in fuel savings. It also does not accelerate as quickly, that is not to say it is sluggish, but it does take getting used to.
 

Kevin Means

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Hi Mike. DEF isn't a fuel additive, it goes in its own holding tank and treats the diesel exhaust before it leaves the exhaust pipe.

We've had three Class A motorhomes over the past 24 years, and the one we have now is our first diesel. Our first MH had a Chevy 454, and our second coach had a Ford V-10. As a frame of reference, when we're towing our Jeep, our 43 foot diesel pusher gets 7.2 MPG at 65 MPH. My brother-in-law has a 34 foot 1999 Tiffin Class A, with a Ford V-10, and he says he's getting about 7.5 to 8 MPG at 65 MPH when he's towing his Jeep.

We're almost 10 feet longer, and probably twice the weight, but we get very similar milege. So yes, newer diesel engines do get better milege than larger gas engines (even newer gas engines.) However, newer gas engines are very reliable, they have plenty of power for most applications and they're notably less expensive to buy and maintain than newer diesel engines.

In my opinion, an RV's build quality, floorplan and amenities are much more important considerations than the type of engine it has, because most people spend a lot more time living in their RV than driving it. As long as an engine is reliable, and provides enough power to carry/tow what you need, I'd focus on  other things and not be concerned about whether it's gas or diesel. Those other things are what drive you crazy.

Kev
 

MikeFromMesa

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Thank you, everyone, for your responses.

We just returned from the RV dealer where my wife decided that she wanted one of the later model Class B RVs and we ended up with a Winnebago Era with the Mercedes diesel. Of course we do not really have it yet, but I did put down a (refundable) deposit to hold it until we are ready to trade in our old 2005 Pleasure-Way gas Class B RV.

I do have some concerns about this, aside from the limited space in the vehicle, mostly stemming from my lack of experience with newer (or, for that matter, older) diesel engines. This is a Mercedes diesel, so who can service it? The sales guy did not know what the service interval was, and I will have to look that up to find out. I have to admit that the vehicle drove like a dream, smoother and more comfortable than my Jeep, it had plenty of power, was fairly quiet and was rock steady on the highway at 75 mph. I ran the generator and, although I could hear it, it was quiet. The dealer says that they service them, but I assume they must be really proud of their work because they charge a lot.

Based on what we had looked at earlier I had thought I might end up with a Ford diesel (meaning I could use the local Ford dealer for service), but that did not happen and my local RV shop will not even do oil changes on the Mercedes diesel because, they tell me, parts are hard to get, expensive and I guess they feel that they do not have the experience to work on them. I will have to see what that means in practice as we put a lot of yearly miles on our RV.

I would appreciate any suggestions.

 

Optimistic Paranoid

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Gizmo said:
But that is Ford Power Stoke, not all modern diesels are created equal.

The guy was talking about $5,000 to fix pump/injectors, or $3,000 to replace turbos.  Even assuming that GMC and Ram diesels are better built than the Fords, I can't imagine the parts are that much cheaper.  I can't afford to spend that kind of money to fix a broken motor. I can get a whole gas engine put in for that kind of money.

I guess there are people who need the diesel's torque to drag a big fifth wheel over the mountains, but most people can get by just fine with a cheaper gas engine.
 

Lou Schneider

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ULSD diesel fuel contains 13% more energy than gasoline:

ww.afdc.energy.gov/fuels/fuel_comparison_chart.pdf

Everything else being equal, a diesel engine will automatically get 13% better fuel mileage than a gasser.  8 MPG vs. 9 MPG, for example. Most reports bear this out, a modern fuel injected gas motorhome gets slightly less MPG than an equivalent diesel.

However, the higher cost of ULSD diesel vs. regular gasoline negates much of the diesels higher MPG advantage.  That leaves maintenance costs, which are much higher for a diesel than a gas engine, even in the smaller engines.  Diesel burns less cleanly than gasoline, creating more soot to be suspended in the oil and requiring larger and more expensive filters to clean it out.

A medium duty diesel like the Powerstroke takes 3 times as much oil and more expensive filters every 5000 miles than the gas V-10, and both give comparable levels of performance.  The V-10 is made to rev higher under load, and it does, but that's the only real performance difference between them.

Engine life is also about equal as far as most RVers are concerned.  When you look at the large number of motorhomes that are traded in after 5-10 years with 30,000 to 50,000 miles on the odometer, does it really matter if a gas engine lasts 150,000 miles or a diesel lasts 250,000? 
 

Optimistic Paranoid

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MikeFromMesa said:
I would appreciate any suggestions.

I think the best thing you could do would be to use Google to find a Mercedes forum.  I suspect you'll learn a whole lot more there about the mechanical end of you're rig than you will on an RV forum.  Hang out here for the house end of things.
 

Lou Schneider

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Most of the higher MPGs obtained by the Mercedes based Class C motorhomes come from their reduced frontal areas and less wind resistance than their American chassis counterparts, not from having a diesel engine.

The Mercedes cab and chassis is narrower than their American van chassis, leading to narrower houses being built on them.  For example, the Winnebago View is only 7'6" wide, a full foot narrower than a typical 102" wide motorhome.
 

rbrdriver

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In response to MikeFromMesa, DEF is definitely NOT an additive to add to the diesel fuel. It goes in a separate tank. If you accidentally added it to the fuel, you're looking at draining your fuel tank, replacing fuel pump, injectors, and God knows what else. So, no, it is not an additive.
 

Gizmo

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Optimistic Paranoid said:
The guy was talking about $5,000 to fix pump/injectors, or $3,000 to replace turbos.  Even assuming that GMC and Ram diesels are better built than the Fords, I can't imagine the parts are that much cheaper.  I can't afford to spend that kind of money to fix a broken motor. I can get a whole gas engine put in for that kind of money.

I guess there are people who need the diesel's torque to drag a big fifth wheel over the mountains, but most people can get by just fine with a cheaper gas engine.

I get that, but the Ford diesels, post say 2000 have had a host of well documented issues including those parts and components mentioned.  But as I mentioned in my original reply and others have as well, diesels irregardless of brand, are indeed more costly to maintain and repair.  The OP should consider that in the decision process.
 

Larry N.

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They (diesels, ed.) have a lot more torque, so they are better going up hills.

I'm not sure I agree with this statement. A gasser can get often get roughly equivalent power at a much higher RPM. In both my Beaver that I used to have (45 ft, 50,000 lbs max, 525 HP) and in my current Ventana (38 ft, 36,000 lbs max, 360 HP), I'll sometimes, if I use the right technique, keep my speed up a little longer climbing long hills in the high country, but sometimes a gasser will soon be passing me -- lots of "depends" here. If the weight and other things were equal then the statement might work, but things are rarely equal.

As far as mileage, the Beaver got 5.5-6 on the level, no wind at 65 mph around 5,000 feet. The Ventana gets 8.5-9.0 same conditions. But stop and go, hills and winds and altitude (thin air has less drag) will affect mpg.
 

Optimistic Paranoid

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I don't know about the diesels used in Class A's, but the Ford Super Duty pickups give you a choice of a 6.2 liter gasoline engine rated at 385 hp and 405 ft.lbs. of torque, and a 6.7 liter diesel engine rated at 440 hp and 865 ft.lbs. of torque.  Looks like a pretty significant difference to me.
 

johnaye

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A rear end diesel is much quieter when driving than a front engine gasser.
 

Frank B

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Optimistic Paranoid said:
The guy was talking about $5,000 to fix pump/injectors, or $3,000 to replace turbos.  Even assuming that GMC and Ram diesels are better built than the Fords, I can't imagine the parts are that much cheaper.  I can't afford to spend that kind of money to fix a broken motor. I can get a whole gas engine put in for that kind of money.

I guess there are people who need the diesel's torque to drag a big fifth wheel over the mountains, but most people can get by just fine with a cheaper gas engine.


To each his own. Our 1 ton 06 Duramax has just over 250k km on it (abt 160k miles) and I've done nothing other than replace a set of glow plugs, oil and filters. It has spent most of its life pulling our trailers up and down hills. And I love the engine braking of this diesel on a long downhill. Seems many are realizing over 300k miles without major mishap.


This is my first diesel, and personally,  I won't have anything other than a diesel for pulling from now on. They are just so relaxed and totally unfazed by the load or the hill. :)
 
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