RVs and Fuel Economy

 Mentioning RVs and Fuel Economy in the same sentence is kind of an oxymoron, don't you think?  After all, RVs are not exactly known for their great gas mileage.

There is a trend in the RV industry today they're calling "right sizing". What it amounts to is an attempt to balance fuel economy with living space and creature comforts for the best value. Some of the new diesel motorhomes and diesel powered tow vehicles claim to get around 18 mpg, a great improvement over the "old days" where similar sized gasoline powered vehicles averaged around 6 mpg -- or less! Of course we pay a huge extra price to buy these new vehicles so payback may take several years, especially with diesel fuel prices climbing.

I mentioned in a previous post the idea of "passenger miles per gallon". This concept is sometimes used to measure efficiency of public transportation like airplanes, trains, and buses. I find it useful to apply it to motorhome or RV travel. My old gasoline powered Class A motorhome got at pretty steady 6 mpg. Seemed like it didn't matter whether I was towing a trailer or not towing a trailer, climbing or descending hills, or sitting the parking lot! But with my wife and six kids on board with me, that yields 48 passenger miles per gallon. Hey, only smaller and highly efficient motorcycles or extraordinary compact hybrid cars can even hope to match that for a single occupant.

Some newer motorhomes and tow vehicles are more fuel efficient than their predecessors.   Smaller diesel powered Class A's are claiming performance up to 18 mpg.  However, I've seen sales literature on 27' diesel powered Class A's from the 1980's claiming up to 14.8 mpg.  Gasoline versions of the same coach got around 6-7 mpg.  Newer computerized, fuel injected motorhomes and tow vehicles give better performance than the old gas hogs I grew up with.  The 1960's were famous for the big, gas guzzling muscle cars, but, ironically, they also produced one of the most fuel efficient motorhomes of all time:  the Corvair powered UltraVan.  It delivered around 15 mpg in a well equipped 25' class A motorhome weighing around 3000 lbs and powered by an unmodified Corvair 6 cylinder gas engine.  It wasn't fast off the line, but owners of surviving "Ultravans" still find the performance acceptable and their aircraft style aluminum construction made them extremely durable and the design was way ahead of its time so it still looks modern.

Fantastic fuel gadgets are pretty much fantasy. You'll see claims for all kinds of devices to improve fuel economy, but most are just scams. There are systems that claim to separate water into oxygen and hydrogen and add the gases into the air mixture. Physics says this will NOT improve fuel economy since it takes a LOT of energy to separate water molecules and internal combustion engines are only about 30% efficient even using the fuels they were designed for, let alone pure hydrogen, which has less energy per unit volume than gasoline. Some other gadgets include magnets that are installed along fuel lines and claim to "polarize" the fuel. There are always tales of super carburetors that deliver up to 200 mpg, but no one has ever actually seen one and fuel chemistry pretty much proves this is totally impossible, regardless of the efficiency of the carburetor. There simply isn't enough energy in one gallon of gasoline to move a vehicle of any size that far.  One device that appears to have some merit is water injection. This simply injects a mist into the air intake. The device was originally intended to clean combustion chambers, but some users found it to improve fuel economy and reduce engine temperatures.  It also reduces pre-ignition, allowing you to run cheaper fuel.  The bottom line: you'll probably save more by not buying these gadgets than you'll ever save in fuel by using them.

There are some things owners can do to improve mileage and performance. First and foremost, is keeping your vehicle in good repair and properly tuned and the tires properly inflated. Exercising cautious driving skills will also help. Avoid "jack rabbit" starts and try to maintain a constant speed.  Use your cruise control (if you have it) when you can.  Improving exhaust and air intake efficiency are among the most popular and productive engine modifications. Banks Engineering provides kits for many applications that significantly improve both performance and mileage. Usually improving one means a decrease in the other, but by increasing the efficiency of both intake and exhaust, remarkably Banks systems usually improve both. These systems are fairly expensive so it may take a while to recoup your investment.  Some modern computer controlled engines can be "super tuned" using modified computer chips, but here again, tuning for power and tuning for fuel economy are usually mutually exclusive.

Keeping your engine well maintained is one of the best ways to coax maximum performance and mileage from you vehicle. Dirty air filters can significantly reduce both mileage and performance. After all, your engine has to breathe, just like you do! To get some idea of the affect a dirty air filter has on on engine, try breathing through a dirty sock. You engine may not care how bad the air smells, but it will care how hard it is to draw it in.  Proper lubrication is critical to prevent wear and reduce internal friction, so religiously follow manufacturer's recommended oil and lube schedules.  Motor oil contains additives to improve performance and these additives break done over time.

Motor oil additives are another way of reducing friction in your engine.  STP is one of the best  know products.  Interesting enough, it is said it was discovered accidentally when folks testing racing engines were looking for a way to accelerate wear,  They tried adding tiny glass beads to the oil to act as an abrasive and it turned out they behaved more like ball bearings to reduce friction.  By the way "STP" stands for "Scientifically Treated Petroleum".  Another popular product I've had personally experience with are the Lucas oil treatments for engines and transmissions.  I once had the air-over-electric shifter on my diesel pusher motorhome professionally rebuilt when it started sticking.  It worked pretty good but began sticking again in less than 3 months.  In desperation I pulled it out and cleaned it myself.  I gave a good dose of Lucas oil before reassembling it and it worked well for more than a year before needed another good cleaning.  The darn thing was nearly 30  years old and had seen over 100,00 miles and probably should have been replaced.  But it would have cost about $2000, IF I could even find one!

Perhaps the next biggest factor affecting RV fuel economy is weight.   As human beings we tend to love our luxuries and comfort and the larger our mobile cottages are, the heavier they are and the more fuel it takes to drag them around.  Minimizing weight by getting rid of unnecessary stuff we accumulate will help keep fuel usage as low as possible.

Keep your tires properly inflated.  Here is something that is really easy to do and can make a big difference in handling and fuel economy.  Over inflated tires can make  rig feel skittish and give it  harsh ride; under inflated tires will make it sluggish, will burn more fuel, and can over heat the tires and cause them to wear and blow out.  Remember the old 55 MPH national speed limit?  It was supposedly designed to save gasoline but reports I've read that even more fuel would have been saved by ensuring proper tire inflation.  Over inflation will cause tires to wear in the middle and reduce traction, making the vehicle feel squirrely .  The ride might be a little softer with lower inflation, but you will pay for it in fuel and risk tire damage if they are too under inflated.  Under inflated tires will wear faster on the outside tread rows and can also have a negative affect on handling.

That being said, driving slower is another way to save fuel.  Transmission problems once forced us to drive our mid-sized SUV at 55 mph instead of 70 mph on a long, interstate trip and our mileage jumped from about 22 mpg to nearly 30 mpg! So, maybe the 55mph speed limit wasn't as dumb as I thought, except for interstate trucks that are designed to operate efficiently at freeway speeds.

Wind resistance can also effect mileage, so minimizing it can help mileage. The boxy shape of most motorhomes give them the aerodynamics of a barn door. Yet you'd be surprised what some of the actually ratings are. I had a big boxy Class A Suncrest with a slightly pointed fiberglass front cap that had about the same co-efficient of friction as a Jaguar XKE! Of course the huge frontal area of the boxy Suncrest compared to the sleek XKE meant the motorhome had a total wind resistance that was still immense when the factor was applied to the total frontal area. I like to give my vehicles the best chance of performing well so I try to keep them clean and well-waxed. It may not seem like a big deal, but given the huge surface area, even a small reduction in surface friction can have a cumulative affect on reducing wind resistance. Ever notice that private planes are always clean and shiny?   One reason is to reduce wind drag.  Keeping your vehicle clean avoids surface grime from turning into micro-sanders at highway speeds and prevents premature paint damage. Besides that, you'll feel better driving a clean vehicle and one day, when it comes time to sell or upgrade, having maintained the exterior will pay back dividends in increased re-sale or trade-in value. Protectall was developed by an airplane owner with a chemical engineering background to keep the surface of his privatge plane in good condition and reduce wind drag. It is popular with RVers too, not very expensive, and fairly easy to apply.

Air tabs.  There is a product designed primarily for OTR trucks to minimize air drag that can be adapted to RVs.  They aren't cheap (around  $2.75 each and you typically need about 72 per RV so figure about $250).  They are kind of triangular plastic devices that are attached to the rear of your RV to manage the air flow behind it or to the cab of a truck to control flow over the trailer.  I haven't tried these myself yet, but the reviews I've read say they improve both  handling and fuel mileage.  It seems to me it would have to deliver a lot of fuel savings to pay back the installation cost but the handling improvements are immediate.  Users have reported noticeable and immediate differences in handling of large vehicles in wind and blow-by from passing trucks.

Another drag on many RVs are the accessories added on top: air conditioners, satellite antennas, storage pods, and luggage strapped into the roof rack. There is not much we can do about air conditioners but we can try to avoid adding other bulky items to the roof. The extra storage is often necessary, but if you can, try to make do with existing cabinets. Adding storage to the roof increases wind resistance. It also raises the center of gravity and can increase roll on corners and susceptibility to cross winds, so keep the weight you put on the roof down to a minimum and choose pods with an aerodynamic shape. Most RVs will have a weight restriction label on the roof near the ladder or a notice in the owner's manual to let you know the maximum weight that can be safely added. Exceeding this weight may permanently damage the structure of your roof and/or seriously affect vehicle handling and safety. And don't forget the risks on your body trying to get heavy stuff up and down from the roof!  I  read of an RVer who planned to carry a spare tire on the roof.  Exceedingly bad idea for at least reasons.  First, the weight and wind drag issues described above.  Second, exposure of the rubber tire to sunlight will speed deterioration.  One tire manufacturer uses the roof of their southern California warehouse as a UV testing facility.

If you tow a trailer, you may want to look into an air deflector to mount on your tow vehicle. You will see over-the-road trucks with steeply sloping deflectors (sometimes built into the cab, sometimes added on). This deflects air so it flows over the trailer instead of impacting the square front directly, reducing wind resistance and improving trailer stability. Add-on wind deflectors are available to fit most popular tow vehicles. I can't speak to how quickly the cost might be recovered in improved mileage, but the increased peace of mind and better handling is immediate.

One of the ways to minimize fuel costs is to reduce the weight being transported. See my previous post "Does your RV  or camp kit need to be put on a diet?" for some suggestions. Take along only what you need. You'd be surprised how heavy that accumulation of little things can be! You really don't need to hauling around the rocks you collected six trips ago or the souvenirs of other trips. And do you really need several pairs of shoes? Tools tend to be heavy, but I find it very hard to lighten my tool box. Still, it is always a good idea to give it a try. If you're carrying around heavy tools you've never needed, you might be able to lighten the load.  Water weighs 8 lbs per gallon.  Having empty holding tanks and only carrying as much fresh water as you need can significantly reduce your rolling weight.

Some "experts" recommend using only name-brand fuels. Off-brands are often cheaper. I recently read an article that stated there is no definable difference between brands and that the off-brand fuels are manufactured in the same refineries and come out of the same tanks as the name brands. They even mentioned that name brand fuels may come from various refineries, such that, for example, fuel you buy at Shell may have been manufactured by Exxon and vice versa. However, name brand fuels usually have proprietary additives that may have benefits.  With all this in mind, I have been using low-priced fuel from off-brand stations whenever I can find it without any noticeable problems. When I'm filling up a 100 gallon RV, a few cents per gallon can add up to a nice savings! Is it worth driving all over town to find the lowest price? Probably not. Even a nickel a gallon for a 100 gallon tank will only amount to a $5.00 savings and you'll probably waste more fuel than that driving around looking for lower prices.

The bottom line is, most of us don't buy RVs for their fuel economy. You may be able to minimize your fuel costs by towing a light weight trailer with a compact car, but if you have a large family or simply appreciate the conveniences of a large travel trailer or motorhome, fuel economy isn't likely to be part of the package. The best we can do is keep our rigs in good condition and drive them in a reasonable manner. Avoid slamming the accelerator to the floor when starting out. Plan ahead for steep grades. Drive at reasonable speeds. Keep weight to a minimum. Avoid wind when you can.

Hills significantly reduce mileage for heavy vehicles like RVs. When you can, plan your routes to avoid steep hills and long grades. An old trucker's trick is to "get a run" at a hill so your momentum can carry you part way up the hill. It works, but don't over do it. You don't want to spend the money you saved on fuel paying a speeding ticket! When you are climbing hills, manually downshift if the engine begins to lug before the automatic transmission downshifts. Even though it forces the engine to run at a higher RPM, it will be more efficient than it will be if it is straining to pull the load. It will save fuel as well as reducing stress on the engine and drive train.

Happy driving!