The gas vs diesel debate will rage on as long as we have a choice of engines in trucks and motor homes. When we were looking at motorhomes (having already heard the Motorhome vs. Fifth Wheel Trailer Debate), we found the choice pretty easy as soon as someone mentioned air ride and air brakes. There is a lot more to this discussion than that though.
Diesel engines are designed to last a long time, usually in the one million mile range. We will never drive that many miles, but it's great peace of mind to know that we can. Diesel engines are large and heavy, so a very robust chassis is required. This means you will have much more cargo carrying capacity in a diesel rig. The motorhome chassis are also capable of towing between 5 and 10 thousand pounds and even more in some very heavy duty applications.
As I mentioned before, most diesel motorhomes have air brakes, usually with front disc brakes and rear drum brakes. These air actuated brakes will give you the stopping power for such a heavy rig. Almost all will have either an exhaust brake or a mechanical engine retarder(Jake Brake) to help bring the coach speed down without having to use the service brakes. This is almost an essential on long down grades. Most also have air bags at each corner to cushion the ride. Some higher end units use this feature to level the coach both when on the road and in a campsite. An exhaust brake is an accessory that can be fitted to most diesel pickup trucks.
A diesel engine is designed to have substantially more torque at lower engine speeds which allows a diesel powered coach to climb mountain grades more easily that it's gas counterpart. This power at lower RPM allows for increased fuel economy as well.
Maintenance on a diesel engine is much more involved as well as more expensive. Oil changes in motorhome can require 20 quarts or more. There will be 2 or more fuel filters, one of which is a fuel/water separator filter. It must be changed each oil change. These intervals are every 5000 miles or annually. On a motorhome, there are air dryer cartridges in each air brake can which must be changed periodically. Cooling system fluid has critical additives for a diesel engine. The heavy duty transmission must have fluid and filter changes on a periodic basis. All these required services can be quite expensive. Most service and virtually all engine and chassis repairs must be made in either manufacturers shops or authorized truck repair facilities. Diesel pickups can be serviced at the truck dealer. This maintenance issue is a major stumbling point for diesel in the gas engine vs diesel engine debate.
At this point in time, diesel fuel is substantially more expensive than gasoline, partially negating mileage gains.
First and foremost is the fact that gasoline
powered coaches are typically 40 to 50 thousand dollars less expensive than a
diesel coach. Gas pickup trucks are at
least $15,000 less. They also can usually be repaired at either a Ford, Chevrolet,
or Dodge dealer depending on engine type. Oil changes can be done by the owner
and require much less oil. There are standard power assisted brakes and usually
no air bags and their associated compressors. Almost all run on standard grade
unleaded gasoline available everywhere and less expensive than diesel fuel. This lower cost issue leans toward gas in the gas vs diesel argument.
Although gasoline engines can produce more
horsepower than a diesel engine, they do not produce anywhere near the torque.
Horsepower may get you to go faster, but it's torque that gets you up the hills
and mountain grades. Gasoline rigs typically have lighter duty chassis than a
diesel rig, so the gas rig will not have the cargo carrying capacity of the
diesel. Virtually all the gas motorhomes produced today are built on the Ford P-53 chassis with V-10 engine of 362 horsepower and about 500 foot pounds of torque. This is first and foremost a truck chassis and rides like a truck. It requires much aftermarket equipment to tame this beast on the road. The front engine is noisy enough cruising down the highway, but screams like a banshee when climbing hills.There is much less basement storage with this chassis over a diesel chassis.
I also cannot in good conscience recommend a gas powered
pickup truck for towing trailers over 12,000 pounds. This alone should shift the diesel vs gas towards diesel power.
It should be obvious by now that I am a diesel motorhome owner. I do tend to go back to my first impressions of "air brakes" and "air ride." I have no prejudice against gas rigs however. Both have their place in the RVing community. Someday we may downsize to a gas rig. I'm afraid this whole gas vs diesel debate boils down to finances.