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Motorhome FAQs

Originally Published in MotorHome Magazine

Over the years, we’ve noticed that certain readers’ questions keep popping up again and again, in similar forms. Some of them come from seasoned motorhome owners; others come from “newbies” who are anxious to get going in this great vagabond lifestyle of ours. In the September 2002 issue, we published FAQs (frequently asked questions), along with their answers, on popular dinghy-towing issues (“Top-20 Dinghy FAQs”). We’ve also received many motorhoming questions that are more coach-oriented in nature. So, by popular demand, we’ve collected a second batch of the most common questions and have provided answers to them. Before we get started, though, we’d like to address a type of request we often receive. Some people ask us to answer their technical questions right away, although they don’t want them published. The purpose of our tech columns is to inform and help as many people as possible by publishing solutions to problems. If our staff spends all of its time on individual replies, we only help one person at a time. Therefore, we publish selected readers’ questions and our answers, which we believe will have wide application:

 Q.  How can we get better mileage without spending money on modifications?

A. First, make sure your motorhome is running properly and efficiently by having it tested on a chassis dynamometer. With gasoline models, have the fuel mixture measured on an exhaust-gas analyzer to ensure that the air-to-fuel ratio is correct across the whole operating range under load. Then, drive slower, with more gradual starts and stops, and make sure your tires are properly inflated.

Q.  What’s the best speed for fuel economy?

A. As you go faster, fuel mileage will drop off steadily. Wind resistance increases with the square of the increase in speed. This means, for example, that there’s four times as much wind resistance at 80 mph as at 40 mph. So the slower the better, as long as the vehicle is going fast enough that its top gear can work. Usually that’s around 50 to 55 mph minimum. You should try testing mileage at various steady highway speeds in increments of 5 mph (i.e., 55, 60, 65) to determine what you find acceptable.

Q.  On average, how many miles to the gallon does a motorhome get?

A. The Environmental Protection Agency (EPA) does not require motorhome manufacturers to test fuel mileage and there is no way to answer this definitively. It depends on the driver, the road and conditions, the make and model of motorhome, engine, transmission, axle ratio, the speed driven, weight carried, etc. MotorHome publishes the mileage of coaches that are tested for the magazine. You can also check with owners of the specific models you are interested in. As a rule, most average full-size motorhomes achieve about 6 to 9 mpg, and a few rare exceptions can go as high as 10, 11 or 12 mpg. Single digits are more likely.

Q.  I want more power out of my motorhome engine. What’s the best way to get it?

A. There is no single “best” way for all models, engine types and owners. We have found that exhaust headers, low-restriction exhausts and air intakes, and computer modifications are quite popular and effective. MotorHome staff members do product evaluations on some performance parts, and the results are published. However, we cannot recommend modifications for individual readers. Also be aware that some modifications may affect warranty coverage.

Q.  I want to put some aftermarket parts on my motorhome, but my dealer says it will void the warranty on the entire coach. Is this true?

A. By federal law (the Magnuson Moss Act), original equipment manufacturers (OEMs) may not void a warranty simply because of the use of non-OEM parts. However, they can refuse to pay for repairs under warranty in cases where it can be proven that the failure was caused by non-OEM aftermarket parts. If a dealer threatens to void your entire warranty simply because of aftermarket parts that are unrelated to the problem area, insist that the dealer personnel put that in writing. In most cases, that will cause them to back down.

Q.  What is the difference between horsepower and torque?

A. Torque is a measure of instantaneous (that is, it is not measured over a period of time) twisting force applied by the engine to the flywheel. Engine torque is typically measured in pounds-feet (lb-ft). Usually, peak torque is listed along with the rpm at which it occurs (for example, 420 lb-ft @ 2,400 rpm). One lb-ft is equivalent to a force of one pound applied to a lever 1 foot long. Horsepower (hp), also sometimes referred to as brake horsepower (bhp), is a measure of work over time that an engine can do. Typically, peak horsepower is listed along with the rpm at which it occurs (for example, 250 hp @ 4,800 rpm). One horsepower will lift 550 pounds 1 foot per second, or lift 33,000 pounds 1 foot in one minute. Horsepower is calculated from direct measurements of torque and engine rpm, using the formula: hp = torque (lb-ft) x rpm divided by 5252.

Q.  The Check-Engine light on our motorhome has come on. I checked all the gauges and fluid levels and they are OK. What should I do?

A. The Check-Engine light, or malfunction indicator lamp (MIL), is supposed to alert the driver when an emissions-system-related problem occurs. There are now literally hundreds of conditions that are monitored, and trouble codes are stored in memory when the MIL is illuminated. If there are any noticeable drivability problems, such as rough running, transmission slippage, etc., or if any gauge indications show that the engine is overheated, oil pressure is low, etc., the coach should be stopped immediately to avoid further damage. However, even if there are no symptoms, driving should be limited until the computer can be scanned by a shop to read the stored trouble codes, correct the problem and turn off the dash light.

Q.  Our motorhome’s tires have plenty of tread left, but there is some severe weather cracking. It appears that the tires crack before they wear out. Would it make sense to buy less-expensive tires if average usage is only 3,000 to 5,000 miles a year?

A. This is a common problem. Rather than buying cheaper tires, consider using tire covers when the coach is parked outdoors. Cracks that are deep enough to reveal the internal cord structure mean the tire is definitely due for replacement. Before going on a trip with cracked sidewalls, have the tires inspected by a reputable tire shop.

Q.  How do I know how old my tires are?

A. Tires are required by the U.S. Department of Transportation (DOT) to have a code imprinted on their sidewalls. The date designation starts with DOT. Before the year 2000, the last three digits of a DOT number represented the week (two digits) and the year (one digit) of production. So, if the last three digits are 229, the tire was produced in the 22nd week of 1999. Tires made after January 1, 2000, have a four-digit date code at the end of the number. The first pair of digits represent the week of production and the last two digits represent the last digits of the year of production. So, if 2200 are the last four numbers, the tire was manufactured in the 22nd week of 2000.

Q.  We are planning to buy a new (fill in the blank). Can you please tell us the best brand and model?

A. MotorHome does not recommend or endorse any brands or products. The information supplied in test reports should be considered, along with other information you gather from direct observation and other sources (such as talking with owners), to make an informed purchase decision.

Q.  The trailer hitch on my motorhome is marked with a 5,000-pound rating. Does that mean it’s OK to tow a trailer or a dinghy vehicle that weighs that much?

A. No, that only means the hitch’s maximum rating is 5,000 pounds. To determine how much weight the coach can tow, subtract the actual weight of the coach, loaded for a trip (with passengers) from the gross combination weight rating (gcwr). That’s the actual weight the coach can tow. Compare that number with the chassis manufacturer’s maximum tow rating; use the lower of the two figures to determine the maximum towable load. Make sure you fully understand the chassis manufacturer’s weight limit for towing unbraked dinghies.

Q.  Recently, the batteries on our motorhome have been draining completely overnight. Are there any steps I can take to determine what may be draining them? Nothing appears to have been left on, and I have recharged them twice and searched for anything left on, with no luck.

A. Remove fuses one at a time and measure current flow across the fuse terminals (when everything is off) with an ammeter set to its 10-amp scale. If current flows, that is the circuit with the draw.

Q.  We have a gasoline-fueled generator in our motorhome that will not start. There appears to be no gas getting to the filter. What can we do?

A. Many motorhomes have a fuel pickup that will not allow the AC generator to get any fuel if the fuel tank is below one-quarter tank. This prevents owners from using all the coach’s fuel and leaving it stranded. Try refilling the gas tank. Sometimes the genset’s float bowl has old stale gasoline in it, which must be purged. If that does not work, the AC-generator fuel pump is the likely culprit.

Q.  I am in the process of restoring an older motorhome and have run into a problem finding parts. Can you suggest where to look?

A. Try checking on the Web at: http://rv.net/obsolete/index.cfm.

Q.  The exhaust manifolds on our motorhome keep warping and cracking. What can we do about it?

A. Excessive heat is the cause. Make sure the fan and cooling system are working properly. Have the air-fuel mixture tested with an exhaust-gas analyzer while the engine is under full load on a chassis dynamo-meter. Also, have the ignition timing checked. Make sure that any factory-installed air deflectors in the engine compartment are in place. In some persistent cases, it may be necessary to replace the iron manifolds with aftermarket headers.

Q.  We own a motorhome with a permanent-mount horizontal propane tank. I was told that this tank is exempt from the new overfill.

A. Yes; only vertically mounted removable LP-gas cylinders are affected by the new regulation. American Society of Mechanical Engineers (ASME) tanks on motorhomes have been equipped with overfill-protection devices for many years.

Q.  Our motorhome’s steering wheel still shakes when driving at highway speeds even though it’s had a wheel alignment. What else could be wrong?

A. Shaking or vibration in the steering is usually caused by one or both front tires being out of balance or defective in some way, not by alignment. Have the front tires and wheels balanced and checked for damage or defects, such as being out-of-round.

Q.  We’re looking for a replacement windshield for our motorhome. Can you help me locate a company that supplies them?

A. Rose City Glasparts Inc. supplies replacement windshields for motorhomes The company is located in Boring, Oregon; (888) 454-9694, glasparts.com.

Q.  Should I start the RV engine every so often during storage?

A. As a general rule, we recommend not starting the engine if the coach is stored for less than six months. Each time an engine is started, water vapor is formed and moisture and acids get into the oil and exhaust system. We recommend the oil be changed prior to storage, and then don’t start the engine unless the coach is driven enough to fully warm it up and circulate all fluids.

Q.  What should be done about the fuel during the time our motorhome is in storage?

A. Obtain a fuel-storage additive designed specifically for either gasoline or diesel fuel from an RV-supply shop, an auto-parts store or a boating-supply outlet. Put in the additive according to instructions while adding fuel. Top off the tank and drive around to further mix the additive before storing the coach.

Q. I’ve always read that tires should be inflated to 80 PSI, but the sticker on my chassis says the front tires should be 65 PSI and the rear should be 80 PSI. Which is correct?

 A. Not all tires should be inflated to the same pressure. The factory recommendations are OK if you don’t know how much weight is being carried. Ideally, the tires should be inflated according to the actual weight carried. If you can’t find individual wheel scales, weigh each axle on a truck scale and divide the weight by the number of tires on that axle. Then look up the correct pressure on the load-inflation table, which can be found on the tire manufacturer’s website or at tire stores.

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