motor home mpg

Floridastorm wrote:
Hello Folks,

I am a mechanical idiot (Contracts Manager my entire career)and know next to nothing about engines with the exception to what I read. Am still considering a motor home for getting around Florida and Georgia in retirement.

Can you help me with the reasoning behind the inability of engine manufacturers to produce an RV engine that can get decent gasoline mileage. I worked with engineers my entire career and don't really understand why they would not want to build this type of engine considering the hundreds of thousands and possibly millions of motor homes built every year. Is it a physical problem or scientific? I would imagine this would address the trucking industry also.

Also, is it better to use premium gasoline compared to regular in a motor home? How about synthetic oil as compared to standard oil?

Florida,

Drew has outlined the issues pretty well, but I just have to jump in here and clear up some things.

The first problem is that you are burdened by a preconceived misconception. It is a physical issue that makes typical motorhomes have less than fuel efficiency you would like. It is a matter of dragging a house down the road. The other issue is that fuel is the least of the issues.

You say you are (were) a contracts manager. I suspect that you used spreadsheets. Open one and put in at least two pages (maybe more) of every way you might choose to travel. If you are not an economic idiot, that sheet will soon show you that fuel cost is just not a big deal. When you add up everything else, it is a just a manageable part of the whole picture.

If you value fuel efficiency that much, go look at the little diesels that are now on the market. There are a few that pretty much sacrifice everything for the fuel economy. The ones that are actually a Class B (van with living space) do even better.

We are currently running a 40+yo gas powered coach, and the actual travel costs are not a killer, the killer for me was the abrogation of the bankruptcy laws in 2009. That is done and there is no way I can recover.

Matt

Floridastorm wrote:
Hello Folks,

I am a mechanical idiot (Contracts Manager my entire career)and know next to nothing about engines with the exception to what I read. Am still considering a motor home for getting around Florida and Georgia in retirement.

Can you help me with the reasoning behind the inability of engine manufacturers to produce an RV engine that can get decent gasoline mileage. I worked with engineers my entire career and don't really understand why they would not want to build this type of engine considering the hundreds of thousands and possibly millions of motor homes built every year. Is it a physical problem or scientific? I would imagine this would address the trucking industry also.

Also, is it better to use premium gasoline compared to regular in a motor home? How about synthetic oil as compared to standard oil?

The problem isn't that the engines are particularly inefficient (though they likely aren't up to the standards of the best auto engines), but rather that moving a heavy non-aerodynamic vehicle around at highway speeds requires a lot of energy. If the engine puts out more energy, it needs more energy (fuel) put in to do that.

There are some theoretical limits on combustion engine efficiency related to thermodynamics (the specific math for which I don't care to take the time to understand, but it's based on the intake and exhaust gas temperatures and pressures and similar operating constraints). There are practical limitations to how efficient an engine can be made based on materials science (how hot or stressed parts may be without failing), operating conditions (the exhaust temperature isn't lower than the ambient temperature), compression ratios (limited in gasoline engines by the tendency of fuels to start to burn prematurely), etc.

Higher octane gasoline is only advantageous if the engine is designed to need or use it. The higher octane rating means that it can have a higher compression ratio before it detonates (i.e. engine knocking). Modern engines with computer controls vary the spark advance and other things to generally prevent knocking, but at the expense of power and efficiency, so some engines will run somewhat better or more efficiently with higher octane gas, and that should be specified in the owner's manual as recommended or required. The gas engines used in RVs generally don't specify anything above regular octane gasoline.

In some cases, premium gas may have more or better additives, or may not have ethanol blended in, which can have their own advantages.

Synthetic oil has somewhat better properties typically than conventional oil (greater resistance to burning/decomposing and such), but would have little if any effect on gas mileage for the same viscosity rating. Using the oil viscosity and service grade as recommended by the maker is all that's required, synthetic or not.

Floridastorm wrote:

Can you help me with the reasoning behind the inability of engine manufacturers to produce an RV engine that can get decent gasoline mileage.

Also, is it better to use premium gasoline compared to regular in a motor home?

How about synthetic oil as compared to standard oil?

Good show. You managed to hit possibly the 3 most prominent "dead horse" issues in the forum......ALL in one post. :B

It is all in here already but:

I takes a certain amount of energy to push a huge weight down the road......especially when the wind catching profile looks pretty much like a barn door (high wind resistance). There just ain't a lot more you can do with the engine itself. This is basic physics.

In all engine applications, you should use the octane that the maker recommends. One is not "better" than the other; it depends on engine design. These days, most are designed for regular. Paying for higher octane is just a waste of money.

Synthetic oil is arguably a little "better" but only by a tiny margin IF you change at the interval recommended for dino oil.

Hello Folks,

I am a mechanical idiot (Contracts Manager my entire career)and know next to nothing about engines with the exception to what I read. Am still considering a motor home for getting around Florida and Georgia in retirement.

Can you help me with the reasoning behind the inability of engine manufacturers to produce an RV engine that can get decent gasoline mileage. I worked with engineers my entire career and don't really understand why they would not want to build this type of engine considering the hundreds of thousands and possibly millions of motor homes built every year. Is it a physical problem or scientific? I would imagine this would address the trucking industry also.

Also, is it better to use premium gasoline compared to regular in a motor home? How about synthetic oil as compared to standard oil?

While you are fretting over fuel cost, you really need to decide what you want to do.

When I started all this years ago, I started a spread sheet. Gas was cheaper and so was everything else, and nothing has really changed. If you buy a good used coach, and do at least the required maintenance, it should last you many years and miles. Tires and fuel are a given too....

But if you add up the traveling cost, any effectively choosen RV can be a winner.

OK, you spend 100$ a day on fuel. But you don't spend 80$ on a motel.
If you have a decent motel, you may get a "breakfast", that only slightly cuts you meal cost for the day. Meals in the coach are what you might eat at home. Same-same there and you can stow left-overs in the reefer.

Then there is:
You never have to unpack.
You always sleep in your own bed.
If you get tired of driving, there are always rest areas and truck stops.

Then there is the thing that we often go to music and other festivals. There are no accommodations available for MILES.

We find it worthwhile even on our budget that has been so vastly reduced by recent events. (Note: no actual political reference.)

Matt

I have test driven that Vegas 24.1 Nice little rig. Kind of a class C and A hybrid. Figure about 8mpg and maybe as much as 10mpg on a good, flat day as that Vegas is only about 25 feet long and therefore pretty light. It is one of the smallest class A's currently being made.

My 25 foot class C on the e350 averages about 10mpg. I drive about 55-60 mph, take it easy up the hills, coast as much as possible on the way back down, and drive defensively.

Another thing that improves MPG is a nice fresh WAX job.. This is why I wax Spring and fall.. Spring I do it here in the south, then drive 800 miles north, Fall, I do it in the north and drive 800 miles south.

The change in MPG is shocking..

The test. Drive at least 100 miles round trip
Wax
Make same trip again
At the start of the trip Gas up, full tank. Note Miles on the old meter
Before the start of the 2nd turn around... Same thing.. Do the math to get actual MPG
At the end of the 2nd Turn Around top off again, note miles and do the math

Prepare to be stunned.

We put a Banks system in ours and it really helped with hills, but I would have had to drive a million miles to make up for the cost.

You know this question is asked often and usually by a 1st poster person who never returns to offer any other conversation to the replies.

When it is so obvious that this is the case (look at all the replies above and still no return of the OP) why do so many participate? :h

It depends more on size and chassis or platform than brand.

Best MPG will be a Type B, a camping van conversion. MPG might range from 19-22 for diesel motorhomes on Sprinter, RAM Promaster or Transit down to 12-15 MPG for B motorhomes on Chevy Express or (no longer made) Ford E-Series. Promaster and Transit vans with gas V-6 engines will be somewhere in between, as will campers built into the VW T4.

Small Type C motorhomes on diesel Sprinter or Transit platforms might give you 12 MPG or better. Winnebago builds a Type A motorhome (Via) on the Sprinter platform that might get MPG in the same range.

The Vegas is built on the E-450 with V-10. Pushing a motorhome size box, this combination might average 7 to 9 MPG depending on wind conditions and driving speeds. My 29-foot C on E-450 with V-10 has averaged 8.3 MPG over 30,000 miles. My worst fill-up was 4.2 MPG, the best 12.0 MPG (must have been a tailwind day).

Larger motorhomes on F-53 chassis tend to do only slightly worse, 6 to 8 MPG. Small (under 26,000 pound) diesel Type A motorhomes do about the same as gas motorhomes in the 20,000 pound to 24,000 pound range. As diesel motorhomes get bigger, they do worse, mostly because the owners tend to use the extra power available to maintain higher speeds. A 60,000 pound motorcoach with 600 HP diesel might get 4-5 MPG on the highway, but folks spending in excess of $2,000,000 for their motorcoach don't worry so much about fuel costs, it is like dealing with the cost of operating a large motor yacht or a private plane.

If you are concerned with fuel costs for something in the size of the Vegas, consider the Winnebago Via as an alternative. But for the extra $50,000 initial cost of a Via, it will take a lot of miles for the fuel cost savings to pay you back, e.g. 500,000 miles if it saves you ten cents a mile.