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Mark, My Words | November/December 2017

Mark, My Words | November/December 2017 1

By Mark Nemeth #45776
Escapees Technical Advisor

Tire PSI Degradation
Q. We are first-time travel trailer owners and have a question about tires. Our travel trailer is a two-tire single axle, and both tires appear to be new. While parked for two weeks, the driver side tire will lose as much as 15 to 20 PSI, and the passenger side tire will lose about 10 to 15 PSI. Even with the lateral wear and tear on trailer tires in relation to the tow vehicle tires, this seems abnormal. If so, what is the suggested remedy?

A. Tires that quickly lose this much pressure have leaks. Normal air loss should only be a few psi per month. It could possibly be a nail or screw in the tread, or a leak in, or around, the valve stems. To test for leaks, spray the tires and wheels inside and out with a soapy-water solution, or take the wheels to a tire shop to be tested.
Loss of Electrical Power
Q. I have a 2014 Thor Four Winds 28Z motorhome. I recently lost all electrical power to the house side while driving down the road. When this happens, the radio loses power and other electrical items stop working. Switching the battery cutoff has no effect, and the normal click of the relay switching is not heard. Each time this happened, the problem corrected itself. While I’m connected to shore power, everything seems to work as normal.

I checked all the fuses/CB on the converter panel, and it’s all working. Is there a breaker on the motorhome that I may be missing?

A. Your problem is a classic symptom of a loose cable or connector somewhere in your house 12-volt system. Do a thorough inspection of all the connections in your battery bank, and check the connections at the 12-volt fuse box. Since you have a battery cutoff switch, check the connections on the big relay for it as well. It may require tracing the cables coming from the battery bank to find all of the connection points. If you can’t find anything loose, the problem may be the disconnect relay itself; however, they don’t fail often. Loose connections or shorts in 12-volt wiring can be a serious fire risk, so if you can’t find the problem, you may want to take the RV to a repair shop.
Mark, My Words | November/December 2017 2

Solar Panels
Q. We frequently dry-camp with our truck camper. It has two 50-watt solar panels installed that produce over 14 volts, but how do I confirm that both panels are producing? They don’t seem to charge the batteries much while we have it unloaded and are gone fishing for the day.

A. The easiest way to test solar panels is with an ammeter. Most digital meters will measure five to 10 amps of DC current, so, if you have a meter, you should be able to test the panels yourself.

Disconnect the hot wire coming from the solar controller to the battery bank. Then, use the ammeter to complete the circuit from that wire end to the battery terminal where it was attached. This will allow you to see the current coming from your panels.

On a sunny day, with your two 50-watt panels in direct sunlight, I would expect to see around five to six amps of charge current. With the meter in place, you can cover, or shade, one panel at a time to see if the current drops to around one half of what the two panels produce together. If you have a low reading, and covering one panel doesn’t seem to make a difference, check the suspect panel for broken wires or damage to the panel.

Mark, My Words | November/December 2017 3

Water Leaks
Q. I have a 2008 Toy Hauler. When the water heater (Suburban) is on, there is a leak where the shower valve connects to the Pex pipe. I replaced the rubber washer/cone on the hot side, and the leak stopped for a while. A few months later, the cold side began leaking when the heater was on. I replaced another washer and the limit switch, and it fixed the problem for a while. The relief valve leaks like the manual says it should. I also bled the system to put an air chamber, as the service manual says; however, it doesn’t tell you which valve to open (hot or cold, or if I should wait until the water is hot) to let air into the system. I never had an issue with it until recently. 

 A. If you experience these leaks only when the water heater is heating up, it usually indicates that the air space at the top of the water-heater tank has been lost. When the water is heated, it expands. If there is not an air pocket in the tank, the pressure in your plumbing system can become extremely high.

Most often, you can re-establish that air space by partially draining the water heater and then allowing it to refill by opening a hot-water faucet. You can also open a faucet briefly to relieve the pressure when the tank is heating up. Unfortunately, that air pocket often seems to disappear over time.

I have found that the best option is to add a small air-bladder expansion tank to your plumbing system. These small tanks, usually only one or two gallons in capacity, are used with reverse-osmosis water systems and residential water heaters in some locales, and they are easy to plumb into your fresh-water piping. The tank can be connected anywhere in the system. Usually, teeing it into one of the cold-water lines is fine. Since it is small, it can be placed almost anywhere, such as under a sink or in a compartment. The tank will absorb any pressure changes, and it has the added benefit of smoothing out your water flow when using the 12-volt water pump. I provide a description on my website, and you can find it at www.marxrv.com/hints.htm#expansion.

Bias or Radial Tires
Q. Should you use bias or radial tires on fifth-wheel trailers? Also, what is an acceptable temperature for tires in use? I’m sure it varies, but is there a maximum limit?
Mark, My Words | November/December 2017 4

A. I have run both types of tires and found that bias are cheaper, but don’t last as long. If you want to use a heavy-duty bias tire, Carlyle is a good brand. They manufacture industrial and commercial tires. Light truck (LT) tires are also fine to use for trailers, but be sure they are rated to carry the same weight. I would stay away from any passenger car tires with the “P” prefix.

Tire operating temperature is affected by ambient and road-bed temperature, so it varies. I feel that a temperature rise of 20 to 40 degrees over ambient isn’t unusual. I see tire temps in the 105 to 115 range on an 80-degree day. They can even rise to over 130 on a hot day. The heavier the load, the more heat generated.

The trick is to use an infrared (IR) thermometer temperature gun to find the average temperature for your tires. If there is a problem, such as under inflation, you’ll notice that one tire is outside the normal range. If one tire is much hotter than the others, begin looking for what’s wrong. It could be a bearing problem, low tire pressure or a brake dragging.

Do You Have a Question for Mark? Submissions must not contain commercial advertising or consumer advocacy issues. Due to the large volume of material and correspondence submitted, we may be unable to reply or acknowledge receipt of your material. Material will be edited. Questions and answers with the highest general interest may be repeated in subsequent issues. Questions can be sent by mail to “Mark, My Words” Column, 100 Rainbow Drive, Livingston, TX 77351-9300 or to This email address is being protected from spambots. You need JavaScript enabled to view it..

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