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Old 05-30-2010, 07:09 AM   #1
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diesel vs. gas

just curious...which gets better mileage, gas or diesel? Also does anyone know what advantages are there to having a diesel engine vs. the conventional gasoline engine? I'm on a trip now and calculated that I'm getting 7.3 mpg and I have no tow and it's a 31 footer. We had the A/C on most of the time.

Is 7.3 mpg good , avg or bad?



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Old 05-30-2010, 07:18 AM   #2
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That is pretty much typical. What speed are you running? If 70 mph, slow down to 65 mph. About the best we got with our 31' class C and the 6.8L V-10 was a bit over 8 mpg at 65 mph.

Yeas a diesel coach of the same size will do a bit better on fuel consumption.

As an example we had a 36.5' fer and pulled it with our 7.3L Ford diesel truck. Total combined weight was about 21000# and we got abour 11 mpg at 65 mph. People pulling smaller 5er with gasoline engines were getting about 8 mpg.


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Old 05-30-2010, 07:43 AM   #3
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We average about 7.5 to 8 mpg with our Class A (8.1L gas) traveling at 65 mph. I have heard DP owners claim anywhere from 7 - 9 mpg depending upon coach length and engine. I really think it's a toss up when it comes to economics. Diesel fuel and maintence costs more than gasoline and gas engine maintence, so even without factoring in the added cost of a DP, the gas probably still works out to be more economical. Sure, a diesel will run for 200,000+ miles, but how many MHs to you see that actually have that many miles? Most clock less than 10K a year!
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Old 07-09-2010, 02:07 PM   #4
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On our most recent trip we saw Diesel prices ranging from $0.22 to $0.36 higher than gas. On a size-to-size comparison, considering an average of $0.29 per gallon difference and the considerably higher maintenance cost of Diesel engines, if you don't get 35% better mileage with a Diesel, gas is more economical. Then, if it's a front-engined Diesel, there's the noise to contend with.

I say this based on what we experienced in our recently traded Alpine 36SDS pusher with a 330 HP ISC and now with the V10 in our Phoenix 24-footer.
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Old 07-09-2010, 02:56 PM   #5
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I read somewhere, on this site I believe, that the 8.1 life expectancy was in the 300,000 mile area.

If that is true, it would be an interesting project to calculate the normal operating costs of a diesel versus a gas engine for that amount of mileage. Using the factory recommended service recommendations for both.

60-65 miles per hour (100 kph for us Canucks) over normal, whatever that is, roads.

BTW diesel fuel is just about even with gasoline up here in Ontario @ maybe a penny difference in most places.
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Old 07-09-2010, 03:41 PM   #6
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One of the things that bother me about the gas/diesel comparasions is that even though the engines in diesel MHs may last for ever nothing else on the MHs do. The A/C, Brakes, Furniture, Electronics and flooring/roof just to name a few are the same as the gas versions. Where is the big advantage for diesel? My God, check out the oil change on gas v diesel. CW has gas at $89 and diesel at $250. I'm not trying to be insulting to anyone here but I truly would like to know where the big difference is.
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Old 07-09-2010, 04:09 PM   #7
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Dewd... The biggest RV gas engine you can buy is a Ford Triton V-10... That motor is just a wee bit, way bit too small for larger Motorhomes. Pickup trucks and Vans have Triton V10's in them. That gas motor should go in nothing larger than a CGVWR of 30,000 lbs and GVWR of 20,000 lbs. (MAX).. Of course you could pull more, but it would be a dog. So if you need power, economy and longevity, you'll need to get a muscle motor diesel.

I had it on a 38 footer and it was a dog. The motor and chassis was way under rated for the 38 footer. The biggest MH with a Triton V10 should not exceed a 24 footer. Max...
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Old 07-09-2010, 04:56 PM   #8
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Another large consideration is the handeling between gas and diesel. Most gas Motorhomes have larger overhangs that cause more movement in high winds and truck passing situations. Thats why they sell hundreds of dollars worth of jimcracks to help get them down the road. There is also the issue of brakes, air verses hydraulic as well as engine retarders. In my opinion it all relates to how much you drive your Motorhome and where. In MY opinion, if you are making shorter trips gas is the way to go. For lots of long highway trips, Diesel is the answer.
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Old 07-09-2010, 05:27 PM   #9
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Year before last when the price of fuel went completely off the charts, diesel cost $0.60 more per gallon. This was a killer. When it cost less to refine diesel than it does gas, this is a real slap in the face. With all of that known, I would still buy a diesel if I had a large, heavy motorhome. You just cannot beat the torque, power and comfort available from a diesel pusher (front end diesel I can't address). If you are trying to push 40,000+ pounds down the road, you are going to want a diesel. The size of your RV, your budget and your expectations will all come into pay when you make your choice.
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Old 07-09-2010, 05:46 PM   #10
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Thanks... I forgot to mention the ride handling. The unit was all over the place in wind, passing, etc.

For tracking... A 45' Tag is the best. It hugs the road like you wouldn't believe compared to others.
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Old 07-09-2010, 05:48 PM   #11
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Ahh.. the good old gasoline vs diesel debate! Each has their own advantages and disadvantages. The whole idea that one is 'cheaper' than the other is mostly personal opinion and based upon that individuals usage of the vehicle.

Personal experience tells me that towing the same trailer and goodies behind my prior vehicle which was a 31' Coachmen with a 460cu in gasoline engine versus towing the same trailer and goodies in our 40' Newmar with a 506cu in diesel is like the difference between night and day. The Coachmen/Ford 7.5 netted me about 7mpg, the Newmar/Cummins 8.3 nets me around 9mpg even though it's over 15k heavier and 10' longer. Not to mention I don't get run over when trying to merge into traffic on the freeway, the wind doesnt blow us all over the place anymore, passing semi's is no longer a sweaty hand affair, plus an obvious variety of extra amenities on the Newmar vs the entry level Coachmen we had.

But see? That's my situation. So in the long run, as others have mentioned already, it depends upon how YOU use the vehicle and what your needs are as to whether or not gasoline or diesel is 'cheaper' for you.
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Old 07-09-2010, 07:55 PM   #12
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California makes a difference as well.

In California the gas rigs need to be smogged, diesel are left alone.

That aside, one must compare apples to apples, if the weight of the rig is in thesame area, then the diesel may be a little more expensive to operate, but even with the weight rating the same the diesel is usually going to have a better torque curve that would give a little better performance for the same vehicle, so 6 of one, 1/2 dossen of the other.

Now as others stated, increase in size requires increase in engine and chassis.

There is clear reason the big rigs are diesel powered, one would not want to take a 5 ton truck chassis and extend it to 40 ft, then build up the suspension to hold the extra weight and have an engine that is running at 85% power rating in cruise on flat ground, you want to start with a chassis system rated to cary the full estimated load PLUS a safety factor above that without any modifications, this usually narrows the choices to diesel.

The short of it is simple, find the floorplan that you want, insure all of the bells and whistles are there, then consider if the chassis system is the best system for the MH you select.

Regardless of the type of power, if being sold by a dealer require the dealer to prove it is the BEST engine for the system, if private party then check here to see how the system is accepted.
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Old 08-10-2010, 05:30 AM   #13
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Originally Posted by inspectorudy View Post
One of the things that bother me about the gas/diesel comparasions is that even though the engines in diesel MHs may last for ever nothing else on the MHs do. The A/C, Brakes, Furniture, Electronics and flooring/roof just to name a few are the same as the gas versions. Where is the big advantage for diesel? My God, check out the oil change on gas v diesel. CW has gas at $89 and diesel at $250. I'm not trying to be insulting to anyone here but I truly would like to know where the big difference is.
First in answering the OP's mpg question, we average 7.5 mpg towing our PT and generally travel between 62 - 65 mph and this includes using the air and generator at times. The difference between the two? Well, the diesel just plain has more power and carrying capacity as well as the air ride suspension.

Now in response to inspectorudy, you have a very viable point about the equipment on board. All of us have pretty much the same equipment on board. Heck my MACA sitting next to a MADP is virtually the same thing. I have all the same ammentities on board that they would have but difference is when you start that power plant on the DP as well as the air ride and the added carrying capacity. Granted the DP may ride ride nicer and bit quieter then mine and especially carry a whole lot more but for the $$$$ difference I just couldn't justify the difference. I also like to tinker with being able to do some maintenance on my own and I feel much more comfortable working on my gas rig as I know nothing about the diesel operation and equipment on board. Not that I couldn't learn but the gas to me just seems to be a whole lot easier of a system and much cheaper to maintain than the diesel. All in all we love our gas chassis, to me it rides and drives great and have to mention that there is not one mod done to the chassis or power plant it's bone stock. One thing I do have to mention though not to counterdict a previuos statement I made about diesel power I sure have not had any problem passing a few of them on grades that I would have not thought possible. HMMM? Well that't my story and I'm sticking to it.
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Old 08-12-2010, 06:56 AM   #14
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are class c 6.6 duramax d alison trans, bully dog chip 11 mpg at 60 mph don't matter hills or flat.pulling car or boat.we went to maine in my unks 94 fleet would flair 454 we average 7-8.now toad

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