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RV Tech Savvy: Gas-Tank Filling Problem Tip

Originally Published in MotorHome Magazine

I had the same problem (as in the March letter) with my 1995 Conquest Class C on a Ford chassis. I discovered that it varied from gas station to gas station. Then I figured out that if I parked at the pump with the front and far side lower than the filler tube, it would fill properly. A lot of the gas stations are not 100 percent level. I assumed that it was a vent tube problem, but could deal with it by circling the pump and coming in from a different side.

Bruce Watson | Bloomington, Minnesota

You know the saying about “assume.” Yes, I’ve experienced this a number of times when filling, and it wasn’t always apparent that there was a slight slope. Thanks for sharing your experience.

Diesel Emissions Maintenance


We own a late-model coach with a Cummins diesel. It amazes me how many Cummins owners are told about adding the blue fluid (diesel exhaust fluid, or DEF) but nobody told them about the preventative maintenance (PM) services on diesel engines. There is an article from Heavy Duty Trucking about the filters for the diesel particulates, which is very interesting. It’s another [thing to consider before buying] a diesel coach with a Cummins engine; taking care of the diesel particulate filters.

Stephen Calderwood | Boring, Oregon

The online article you referenced, “What You Should Know About After Treatment System Maintenance,” at www.truckinginfo.com, is aimed at trucking fleet operators and assumes that the vehicles will reach high mileages typical of commercial trucking. As the author notes: “ … diesel particulate filters, diesel oxidation catalysts, selective catalytic reduction systems and their associated hardware have proven pretty reliable over time.” The article goes on to state that the estimated safe diesel particulate filter cleaning interval is more than 350,000 to 400,000 miles for most trucks. The vast majority of motorhomes do not rack up this kind of mileage, so this should not be of great concern to most typical owners. Adding DEF can be a nuisance, but the cost relative to the overall operating cost of the vehicle is not that significant, and makes a huge difference in reducing exhaust emissions and therefore cleaner air.


Thermostat Mystery


We own a 2005 Fleetwood motorhome with two Coleman Mach 3 air conditioner units controlled by a single Coleman RV Comfort ZC digital thermostat. Two to three times a year, while running the units, our thermostat will make a popping noise and will instantly give a digital readout of “00.” This effectively shuts off any cooling, as it turns off the compressors. It does, however, allow the fans to continue running. If we are in the motorhome this is no big deal, as we can reset the thermostat by momentarily turning off the house batteries, but this could spell disaster for our dog in hot weather if we are away. When this first started happening, I contacted Coleman and got in touch with one of its engineers. The engineer said that although this problem is rare, it does happen from time to time on some RVs. He told me that there is some sort of radio frequency interference (RFI) inside my RV, which is causing the thermostat to go into diagnostic mode. He kindly sent me the latest thermostat and radio noise choke filter, free of charge. When this did not help, I called him back. He told me the following items could be causing the interference: fluorescent tube lighting, TV antenna booster, bad inverter/charger and CB radio. I removed all the fluorescent tube lighting and replaced it with LED strips. I replaced the TV antenna booster with a KING Jack antenna and booster (I power down the booster when the RV is unattended). I eventually replaced the Xantrex Freedom SW inverter/charger (when it quit working) with a Magnum PSW inverter/charger. My CB radio is a non-issue, as it is only used while traveling. Another RV tech told me that any battery charger can emit a radio frequency, so he told me to disable my Magnum’s battery charger when it is not needed, which I have. Unfortunately, none of the above measures have solved my problem. I have been dealing with this issue for years. Can you help?

Craig Post | Upland, California

What you describe is a known problem with this unit, and you’ve pretty much exhausted most of the common fixes for this. You may be near a strong external source of RFI, which is beyond your control. Another possibility is that you have an intermittent faulty connection. I suggest checking all the connections and wiring to the air-conditioning units, circuit boards and thermostat as carefully as possible. Of course, make certain you have a good 12-volt DC power supply, and consider buying a desktop 12-volt DC power supply. Then, wire the system to that, instead of the coach power supply, and test it to see if it still happens. Next, I would consider replacing the control boards, one at a time. Buy one new board and replace one, but keep the old one. If it happens again, swap the second one and test it.

LP-gas Line Flex


We own a 2008 Jayco Melbourne, which we really like. It has a propane stove in the slide and I wonder if the process of opening and closing the slide puts any fatigue on the gas line. Do RV manufacturers take any preventative measures to prevent fatigue and avoid a rupture?

Terry Chellis | Wooster, Ohio

RV LP-gas systems have flexible hoses wherever they must flex or bend. These are typically well-made and have a good track record of holding up. However, it doesn’t hurt to inspect them from time to time. I suggest you add this inspection to your checklist, especially if the motorhome has been stored for a while.

F-53 Ford Noise

In the March issue, you responded to a two-pronged question from Mark Schall (“Concerns on an F-53 Ford”), the second part of which had to do with a loud noise coming from the engine of his Ford V-10 6.8-liter on the F-53 chassis. We, too, are the owners of a Fleetwood Bounder 33C with that engine, though ours is on a 2013 chassis (2014 Bounder model year). We bought the unit used with 20,000 miles on it last summer. When going up a 10,000-foot elevation pass with about a 7 percent grade, we had the same issue Schall did. All of a sudden, a loud noise came from the engine (you can describe it as a whistling, or a jet taking off). It scared us, but we didn’t lose power and no gauges were showing abnormal. We went over the hill and everything quieted down with no more problems.

Upon returning home, I did some searching online and saw that others had the same issue. However, there seemed to be no solution found, but the word seemed to be that at high load the fan clutch kicks into overdrive, causing the noise. By the way, we did check that all the belts were tight when we returned. Last winter we went down to Arizona, and climbing the mountains I kept the speed and rpm down, and once I heard the engine start to act up, I slowed down before it started up again. In summary, if you could track down whether this is something that is “just the way it is” or if a fan clutch may be bad, there are a whole lot of people who have that issue that would love to know. Climbing a 10,000-foot pass with the doghouse cover off to see if it will do it again is not really a viable option.

Nick Spence | Durango, Colorado

The noise describe as “a jet taking off” is almost certainly the mechanical fan coming on when the fan clutch engages or, as you describe it, “kicks into overdrive.” Normally it freewheels until a temperature sensor causes the fan to engage, which usually occurs on long climbs and in hot weather. It’s perfectly normal and, in fact, necessary to keep the engine cool enough for safe operation. The noise level also usually increases when climbing a grade due to downshifting, which raises engine speed.


Ken FreundRV DIYRV TechRV Tech SavvyTech topics

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