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RV Tech Q&A: April 2018

Originally Published in Trailer Life Magazine

Slideout Roof Sealant

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What do you recommend to seal an RV’s slideout roof? Does this need to be done, and, if so, can you use the same product on the main roof or something else?

Glenn Brown | Willis, Texas

Answer iconBy “seal” the roof, I’m guessing you mean regular maintenance and treatment. Yes, it should be done. If the slideout roof uses the same material as the main roof, follow the same maintenance procedures, material and schedule.

If the slideout roof is a different material, research the maintenance suggestions for that material and follow the manufacturer’s recommendation.

Higher Load Range Tires

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I appreciate all the information you have provided regarding RV tires in past issues. I now have a much better understanding of the importance of good tires and tire maintenance. Given that I have only two trailer tires between me and a breakdown on the side of the road, I have a question about the load range rating of the tires that came on our 18-foot Jayco Jay Flight, which are 205/75R14, load range C. When I replace the tires, would there be an advantage to upgrading to a higher load range or wider tire? Seems like that would give us a little more protection.

Robert Turner | Bowling Green, Kentucky

Answer iconIt’s almost always a good move to upgrade to a trailer tire with a higher load rating, Robert. I say “almost” because I suppose somewhere out there in trailer land there’s a person who had a bad experience due to such an upgrade, but I can’t think of any reason why it wouldn’t work. Yes, such an upgrade, to a tire with a higher load rating, will give you more margin of safety for carrying the trailer and its cargo. You mentioned getting a wider tire, but that’s not generally a goal when an upgrade is considered, because it doesn’t gain you anything as far as performance, longevity and such are concerned. A higher-capacity tire may ride somewhat harder by a small degree, but that’s not a large concern and is well worth the tradeoff of greater reliability and safety.

You have two technical considerations when looking at a tire upgrade. First, the tire must fit the allotted space and not contact the wheel well, exterior-body wheel lip or, in the case of dual axles, the other tire. Second, the wheel also has a load rating. If, for example, your trailer’s original wheels are rated at 2,800 pounds each, and you mount tires rated at 3,400 pounds each, you could overload each wheel if you take advantage of those new tire ratings.

You’ll find the wheel ratings stamped somewhere on the hub or rim, probably on the back side where it doesn’t affect the wheel’s cosmetics, and that can help you decide if replacing the wheels is on the agenda, too.

Trailer and Tow Rig Plugged In?

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This is in regard to the “Tow Rig Plugged In?” question and answer in July 2017’s RV Clinic. I have read the answer several times and am still confused. Under the “easy test” (second paragraph of the answer), it seems to say the engine is running both times you test the plug to see if there is power to the towed vehicle. I would appreciate anything you can explain to clear up this confusion.

Bonnie Kindig | Rittman, Ohio

Answer iconWow, Bonnie, you have every right to be confused about this. The answer as printed was incorrect, which sometimes happens with a technical-related subject, and we apologize for any confusion this may have caused. That second paragraph should have read “With the engine turned off and all the truck lights off, touch the negative cable….” This engine-off test would be followed up with the engine-turned-on test to provide the information you need.

Tundra Brake Results

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This is in response to David Chapman’s “Tundra Brake Problems?” letter in February’s RV Clinic. We have owned two Tundras that have pulled travel trailers — previously, a 2007 Double Cab 5.7-liter and, currently, a 2013 Double Cab 5.7-liter 4×4. The trailers ranged from 36 feet and 8,600 pounds down to 26 feet and 6,000 pounds. Our current unit is 30 feet and 7,000 pounds. The 2013 has 32,000 miles on it, most of which are towing miles. A recent dealer inspection indicated very little brake wear. I was told they look almost new!

The 2007 had 118,000 miles with no brake issues. I always test the brake controller prior to getting on the highway. When descending a 6 percent grade, I use the transmission and downshift with little braking. I was told by the dealer not to worry about “overusing” the transmission, as it’s very durable. We also use an Equal-i-zer hitch with a 14,000-pound head; it’s very stable.

Marc Olson | Sun City, Arizona

Answer iconThat letter and our response generated a lot of reader mail, Marc, both detailing Tundra brake problems and, in some cases, such as yours, referring to those with better brake results. Based on Tundra truck forums and such, there is a lot of owner disagreement on this. A truck with brake-wear problems, towing or solo, such as the rear brakes not wearing quickly enough and the front brakes wearing too fast, overheating the rotors, or both, is a tough situation. One answer is that the truck’s proportioning valve is set up or adjusted incorrectly. If it doesn’t send enough braking force to the rear brakes, the driver has to depend too much on the front brakes, with easily predictable results.

On an average passenger vehicle, the front brakes do a larger percentage of the work than the rear brakes, so the proportioning valve is adjusted to accommodate that. If the proportion is wrong, not only do the front brakes wear faster and possibly overheat and warp the discs, it also can result in an unsafe driving situation because of the uneven braking force, front and back. This is the kind of adjustment a trained dealer specialist would need to inspect and verify. If it’s done incorrectly, the result can be dangerously out-of-whack brake proportioning. Leave it to a pro.

Trailer Tire Loss

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I have a 2006 Northwood Arctic Fox 33A trailer connected via a Hensley Arrow hitch. Traveling down Interstate 95 in South Carolina, a car with a smashed front end pulled up beside me yelling that I lost a tire. We did not feel any sway at all with the missing tire; the Hensley hitch did its job. The rear axle was missing a tire that smashed into the car, but luckily no one was hurt. They said the trailer had lost the tire about 1 mile back.

After exchanging information, I slowly drove about 2 miles to the exit. All the studs had been sheared off. The lesson here was to check all lug nuts when stopping for fuel.

When we stopped to work on the trailer, I noticed that the water heater, located in the front-right corner, had pulled away from the trailer body, about 1 inch or so on the top and ¼ inch on the bottom. The water heater is installed with one screw on each side into the aluminum frame.

Also, when we went to open the slide, which is a full living room/dining room slide, it shuddered and bounced while opening. This slide is gear driven from under the floor. From the trailer bouncing down the highway for a mile, is it possible that the aluminum-frame structure that makes up the trailer body shifted and is now out of square?

Mark O’Connell | Rockledge, Florida

Answer iconAll things considered, it sounds like you made out fairly well with the tire loss, Mark; it could have been a lot worse. It’s possible your trailer body was tweaked a bit, but, if so, I don’t think it was due to the tire loss. Even with just one tire supporting the trailer on that side, the weight is still bearing on the part of the chassis designed to carry the load via the suspension component mounts. A couple of miles of stress on a smooth paved road aren’t going to twist the frame that much. It would likely require many miles of travel, and perhaps bumpy road conditions, to do that.

The stress and impact of the tire joining the birds could have jarred the slider mechanism, without twisting the entire trailer frame, and caused the shuddering you experienced. You’ll need to have an authorized service center take a look at the trailer and examine the slideout for another problem such as an out-of-adjustment gear drive.

As for the water heater coming loose, that could be an installation problem when perhaps the factory worker didn’t add all the required screws. Just two screws, as you described, doesn’t sound like enough for a proper installation. That, too, should be checked by your service center to verify that no damage was done to the heater while it tried to come loose.

Fridge-Fan Failures

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Regarding February’s “Fridge-Fan Use” letter, I purchased a 2016 Keystone Montana High Country that has the refrigerator located in the slideout of the kitchen. When the outside temperature gets to 90 degrees Fahrenheit, the fridge won’t cool below 40 to 45 degrees, which will not keep food safely.

The factory had installed three fans to blow the hot air up to the top of the slideout. I put a fan inside the fridge, and it helped a little. I also put two fans to pull the hot air from behind the unit, but nothing really helped. I contacted Dometic, and they said there was no reason for it not to cool properly.

It still doesn’t work right, so we get to use it only in the early spring and late fall when the temperature is below 90 degrees outside. Any advice you can give would be wonderful.

Donnie Holland | Ware Shoals, South Carolina

Answer iconWhen installed in the RV’s body, the upper air vent is installed in the roof, and natural convection causes the cooling air to be drawn in the lower access-hatch openings. It moves up across the cooling coils, then up and out via the roof vent. When installed in a slideout, with the upper vent installed in the slideout side wall, the convection airflow is not as efficient because the heated “exhaust air” has to flow up past the cooling coils, then out at a 90-degree angle to the natural convection flow. That’s why so many RV manufacturers use auxiliary cooling fans with refrigerators installed in slideouts.

Given that you have five fans installed to help your RV’s fridge, I’d say the cause of poor fridge performance lies elsewhere. It can be as simple as something blocking the cooling airflow passage behind the fridge. Dometic has dimensional standards required for RV fridge installations, including the airflow chamber behind the fridge, and it’s possible the manufacturer might have fudged this space a bit. A look at the installation requirements in the owner’s manual and measuring the space could verify or eliminate this as a cause. If the space is too tight, you may need to figure out a way to remount the fridge so it allows more air circulation over the coils. If the space is too open, baffles will need to be installed in the cabinet to help direct the air and keep its flow within the coils.

You should also check the refrigerator’s input voltage to make sure it has an adequate power supply, and have a trained LP-gas technician verify that it has 11 inches water column (wc) of gas pressure available. You didn’t mention which model refrigerator you have, or if the cooling issues were on AC mode, LP-gas mode or both, but if the refrigerator has two AC elements, it’s possible that one of them has failed. These things, if not up to spec, can also cause a refrigerator in good condition to operate at a less-than-optimum performance level.

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

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Jeff JohnstonRV ClinicRV DIYRV Questions and AnswersRV TechTrailer Life RV Clinic

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