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This is an old argument but a good question that I pondered myself when purchasing my first coach. 100 people will have 100 different opinions. In general, Diesel’s will get better mileage than gassers. This is because diesel fuel has more carbon atoms than gasoline. What does this mean…allow me to give you a little science and tie that back in to your choice…
When fuel burns it is the carbon bonds in the material that release the bulk of the energy to do work. This is a universal relationship, regardless of the fuel (gas, diesel, propane, alcohol, wood, etc.). The easy way to think about this is that something like wood has many, many carbon bonds and propane has 3, gasoline somewhere between 5 and 12 and diesel from 10 to 20. What is a carbon bond? It is the attraction of the carbon atom to some other element, like hydrogen. The human body has billions and billions of carbon bonds, but I don’t recommend burning them as fuel in your RV ;-).
Each of these carbon bonds, when broken, produces energy. Heat in the case of something like firewood and heat and work in the case of an engine. The trick is that the engine captures the energy and turns it into work like turning the wheels.
According to the Department of Energy Diesel has about 13% more energy per gallon than Gasoline. B100 has about 3% more energy per gallon and B20 has about 9% more energy per gallon of gas. (http://www.afdc.energy.gov/fuels/fuel_properties.php)
So with all things equal you can expect to get about 13% better gas mileage with a diesel engine than with a gasoline. If your driving lots of miles that may make sense. Also, in general, motorhomes less than 37 feet will usually be gas with optional diesel. Longer than 37 feet I DO NOT recommend a gas engine and usually they are not an option in the first place. Depending on the size you get you may not have a choice but don’t fret. You can’t go wrong getting a diesel coach. More on that in a bit.
As Pippi mentioned maintenance is everything regardless of the fuel you use. The maintenance cycle (time between oil changes, etc.) is a little longer with a diesel than a gas engine but they can be more expensive to fix when they break, and they will break… so be prepared and do not cheat on your maintenance… Keep your tires inflated correctly, change them regularly <Pippi>, change the oil and filters on the schedule published for your coach, lubricate the chassis regularly and use good quality fresh fuel. Pippi has a ton of videos on YouTube showing you how to do the maintenance yourself. Also consider a good fuel treatment (gas or diesel) with every tank to help keep the engine internals clean. It’s a cheap investment but can save you tens of thousands in repair costs.
Some may argue that diesel engines are dirtier than gas. I look at carbon footprint when I think about this. If you’re looking at reducing your carbon footprint and treating the environment right you still won’t go wrong with a diesel. This is particularly true now that they mandated low sulfur content that is available today. I won’t bore you with another chemistry lecture, but google it and you will see what I mean.
As you mentioned you want to run bio-diesel and that combined with the increased mileage creates a smaller carbon footprint than similarly equipped gasoline engine. This is true with just plain diesel as well. I made it a point to buy bio-diesel when could. I read an article awhile back that compared this in RV’s, but I just can’t put my finger on the link. I’ll dig that up and update this post when I find it. Also, DO NOT use homemade bio-diesel in your RV and if you do get a diesel try and avoid buying it from convenience stores and such. That fuel can sit in the tanks for weeks or perhaps months. It often will contain water and other contaminants and that can cause you a ton of trouble just to save a couple of cents. Go to the truck stops and buy it there. They sell tons of it so the fuel is always fresh and usually good quality. If you want to save some money look into RV loyalty programs offered by Pilot/Flying J, Goodsam, Travel Centers, etc. You can usually save 3 to 8 cents a gallon with your rewards card and you rack up points to use for discounted propane, free dump station use, free showers, coffee, etc.
One other thing to note while I am thinking about it, gas mixed with alcohol will get poorer mileage than just plain gas. Most alcohols only have 3 or 4 carbon bonds and when you add this to the gasoline the concentration of carbon bonds is reduced so it produces less ‘work’. This is true with propane and natural gas vehicles as well because propane has 3 bonds and natural gas (methane) has one bond. They burn cleaner but you use more fuel to do the same amount of work because there are fewer carbon bonds to break, but the carbon footprint is only slightly reduced because you are burning more fuel.
Finally…they said..Phew TR..IMHO, I would chose diesel over gas for a motorhome anytime. You will get much better performance and mileage and provided you are doing your maintenance regularly and using good fuel you shouldn’t have too much trouble.
Hope this helps. Be sure and check back in and let us know what you decide.
Peace
TR
