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RV Tech Q&A: September 2019

Originally Published in Trailer Life Magazine

Vintage-Trailer Welding

Red letter QI have an older classic-style trailer, almost canned-ham vintage. The hitch frame is made of heavy channel steel rather than the box steel tubing used today. I want to replace the stock hitch coupler with a new one with a better, more reliable latching mechanism. Is it safe to weld things to that old steel frame, or can that damage the metal’s strength?

Mounte D’Anjoy | Oregon City, Oregon

Green letter A

Sure, it’s safe to weld on that new coupler. Adding safety is always a good idea! Be sure to work with a reliable and experienced fabrication shop because it knows how to perform welding without compromising the steel temper, which would likely be your only structural concern. A hitch shop can also help you choose a new coupler assembly that’s rated to handle the trailer’s weight. They come in all sizes, and you’ll need one that’s rated for your RV’s gross vehicle weight rating (GVWR), or somewhat more, as a safety factor. And finally, don’t forget a new pair of safety chains while you’re at it.

Tires and Axle Ratings

Red letter QMy fifth-wheel’s axles are rated at 7,000 pounds each, and the fifth-wheel is rated at 14,500 pounds gvwr and cargo not to exceed 2,691 pounds. The tires are E-rated with a 3,520-pound max load rating each. The axles are not rated to carry the maximum allowable weight, and the tires are not rated to carry the maximum total weight either. The tires are rated to carry the axle weight.

Can I get G-rated tires and exceed the axle weight, or just keep the E-rated tires and not exceed 14,000 total pounds? How important is it not to exceed the maximum axle rating?

Don Meier | Alpine, Utah


Green letter A

To clarify a few points on this, your tires can carry a maximum of 14,080 pounds. Your fifth-wheel’s axles and tires are OK, even though they total up somewhat less than the trailer’s gvwr because the axles do not carry the entire trailer weight. About 15 percent or more of a fifth-wheel’s weight is carried on the hitch, and the axles support the rest of the trailer’s weight. It’s important not to exceed the axle rating to avoid overload-related mechanical failures.

As for the higher-rated tires, sure, you can go with the new tires, but you’ll also probably need to replace the wheels because the old wheels may not be rated high enough for the new tires. You need to consider a “system” approach when making mechanical changes such as this rather than just one component.


I read the response to Claude Messier’s question, “Greasable Shackles,” in the June issue about possible clogged zerk fittings on his trailer’s suspension. Your advice was correct as far as it went.

Grease guns are old school, and I’m an old mechanic. The grease gun’s head is similar to a drill chuck. It has jaws inside that are held by spring tension. Most often, this tension is enough to keep grease from “blowing by” the zerk. If blowby occurs (as it did for Messier), place the gun on the zerk, then twist the outside collar to tighten the gun’s jaws. This will increase the pressure of the zerk-to-gun seal. The collar will have to be loosened to remove the gun and can then be readjusted to enable routine, push-on attachment.

A. Wright Ellis III
Richmond, Virginia

Thank you for that suggestion! I’ve used an older grease gun for many years and always wondered about the knurled handgrip part of the head. We can learn something new every day, and your information will be useful to other readers as well.

You need to take your trailer to a public scale when it’s loaded and ready for a trip and weigh it to determine its overall weight, the weight on its axles and the weight on its hitch. Those manufacturer unloaded vehicle weight (UVW) figures are almost worthless when it’s time to get down to brass tacks with figuring out where you stand on cargo-carrying capacity, tow-rating suitability and so on. People don’t go RVing and travel with an unloaded trailer, and that uvw figure often doesn’t include the weight of some dealer-installed or even factory-installed options. After a trip to a certified scale, such as a CAT scale at a public truck stop, you’ll know exactly where you stand on weights, and then you can make your calculations based on facts rather than factory estimates.

Residential Fridge on the Road

Red letter QWe have a 2017 Heartland 3870FB with a residential refrigerator. We tow our Heartland with a 2015 Ram 3500 6.7-liter Cummins. Can we run the fridge while driving down the road? I’d like to know if I can turn it on at the start of a monthlong trip and leave it on, powering it off only when switching to shorepower. I have read several online posts and read blogs. Some say yes, and some say no.

Bob Carter | Benson, North Carolina

Green letter A

There’s nothing wrong with running your RV’s residential refrigerator while on the road, as long as your trailer’s 12-volt DC system is up to snuff. The fridge operates off 120-volt AC power from an inverter, which in turn is powered by 12 volts DC from the battery bank in your trailer. When on the road, the truck’s alternator should keep up with the charging demands, but when in an RV park, the refrigerator will work on available 120-volt AC hookup power.

If you plan on spending time without hookups, you may want to consider adding a large solar-panel array and charge controller to the trailer, something, for example, in the 800-watt to 1-kilowatt range.

See Related Story:
RV Clinic FAQ:
Top 20 Tech Questions

A company specializing in mobile solar-charging equipment, such as AM Solar in Springfield, Oregon (www.amsolar.com), can help you determine exactly how much solar-panel capacity you’d need to do the job.

Solar panels work just fine traveling or parked, and would help take a chunk of the charging load from the truck’s alternator as well as keeping the batteries up if you need to park somewhere without shorepower hookups now and then. Of course, in lieu of the solar panels, you can use a portable generator if you’re in a location that allows generator use.

Three-Way Refrigerators

Red letter QHow come trailer manufacturers don’t put three-way refrigerators in their trailers? I have been told many times that you shouldn’t tow a trailer or fifth-wheel with the refrigerator operating on propane just in case you have an accident. If a propane line should break, it could be catastrophic. When going on a long trip, I can’t keep the refrigerator cold if the propane is off.

John Sullivan | Vail, Arizona

Green letter A

Some RV manufacturers do use three-way refrigerators, John. If they aren’t standard equipment, they sometimes offer them as options, but they’re fairly rare these days. As for using a propane-powered appliance when driving, that’s a matter of widely disputed opinion. Many people keep the fridge going on propane; others don’t. Propane systems have excess-flow prevention valves. If there were a major line break and potential leak, the valve would shut down the flow right at the supply cylinders.

The cylinder would need to be severely damaged and ruptured to permit a significant gas leak. The most serious safety consideration is that the propane supply and the appliance (in this case, the refrigerator) are turned off before refueling the tow vehicle to avoid an explosion caused by gasoline fumes being ignited by the fridge burner. In the end, the choice is yours whether or not to use the fridge on propane while traveling.

Have a Tech Question?

Email [email protected] and include your full name and hometown. Selected letters will be answered in the monthly RV Clinic column, but time does not permit individual replies.

Man with grey beard and blue shirt leaning over car hoodJeff Johnston served as technical director of Trailer Life for 20 years and has been an RV enthusiast, mechanic and writer since he could hold a wrench. In his monthly RV Clinic column, Jeff replies to Trailer Life readers’ technical questions about RVs and tow vehicles. He also serves as associate producer of Rollin’ On TV, a nationally syndicated television program for RV enthusiasts.

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