Q: I have a 2002 Tiffin Zephyr motor coach. I am looking for a supplier that sells an electrical monitoring system that will automatically start my generator when the house battery voltage reaches a preset or low-voltage level. I have seen this on other motor coaches, but so far I am unable to locate a manufacturer for this product.
Ronnie Smith, F298700
A: I have been able to locate two companies that make an auto-start circuit board “” meaning that when the battery voltage decreases to a preset value, the circuit board will (preheat if a diesel) start the generator, allowing the batteries to charge for a predetermined length of time and then will turn off the generator. The companies are Dyna Gen, (902) 562-0133, and Westhaver, (410) 792-2823. They sell primarily to RV manufacturers and may refer retail business to a dealer, as the installation is not a plug-and-play but requires rather complex wiring. The Power Tech Company “” (352) 365-2777 “” uses the Dyna Gen and might be able to help with a wiring diagram.
Is More Too Much?
Q: During the past several years, there seems to be a race to increase engine horsepower in motorhomes. Have you published any articles about tuning down for better fuel use? Can you direct me to a source for this information?
I have a 350-horsepower Cummins engine, and I think it is too much horsepower for our 39,000-pound coach. I have contacted Cummins but have received no reply.
Dave James, F299252
I believe you are the first person I’ve ever heard from who believes he has too much horsepower; most people not only want more, they demand it. However, the inquiry on how much horsepower is too much still escapes a definitive answer. The solution appears to identify an appropriate power-to-weight ratio. Determining the torque-to-weight ratio might be more representative, but it’s a bit more complex and more difficult to research, so let’s consider horsepower.
A: I talked with a representative from the Recreation Vehicle Safety Education Foundation to get some ballpark numbers on the weights of diesel pushers. The numbers have quite a range, depending on length, slideouts, the chassis, and other factors. But since we’re simply looking for an average, the popular weight range of these motorhomes is between approximately 27,000 pounds and 36,000 pounds.
The popular horsepower range is 300 to 400. If you add a 3,000-pound car as a towed vehicle to the back of the motorhome, you would get a ballpark ratio of around 1 horsepower to every 100 pounds of weight. This is a horsepower ratio that I would use as the minimum, and for someone who frequently travels in mountainous areas a great deal, a ratio of 1 horsepower per 90 pounds would have more appeal. In that case, a 33,000-pound motorhome plus a 3,000-pound towed car (36,000 total pounds) divided by a ratio of 1 horsepower for every 90 pounds would require an engine in the 400-horsepower range. A like rig operated primarily in non-mountainous terrain at a 1-horspower-to-100-pounds ratio should provide acceptable performance with an engine in the 350-horsepower range.
By using this formula with your 350-horsepower engine and 39,000-pound motorhhome, you can see that your horsepower-to-weight ratio (1 horsepower to 111.4 pounds) is even slightly lower than my minimum.
Q: We own a 2000 Tioga motorhome with a 4,000-watt Onan generator. The generator only has six hours of run time. However, it seldom runs smoothly, and most of the time it surges. Do you have any suggestions as to what we should look for?
Sherwood Dusterwinkle, F292777
A: I checked with Onan, and according to the company’s technician, the generator has not been used enough. To keep the carburetor clean, to prevent fuel varnishing, and to keep the engine lubricated and free of condensation, the generator should be started and allowed to operate under at least a 50 percent load (i.e., 2,000 watts for a 4,000-watt genset) for two hours every four weeks.
Fuel varnish is the gummy residue that forms in the carburetor when fuel gets old and breaks down. Fuel varnishing can clog the small passages in the carburetor, making the genset hard to start and run poorly, even though it may have low operation hours. Before taking the genset to a dealer for repair, I suggest running a quantity of fuel that has been treated with a fuel system cleaner through the genset. If that does not get rid of the symptoms, the genset may require a new carburetor.
Since Onan has no control over the fuel quality or the amount of time the genset is used, problems caused by fuel varnishing are not covered by the Onan warranty. That’s why it’s important to protect your investment and exercise the genset regularly as recommended in the operator’s manual.
You also may want to post your own generator questions in the Ask Onan forum on www.funroads.com for an answer direct from the company.
Let The Four Winds Blow
Q: I’m having the same air-conditioning problem with my 2001 Four Winds motorhome as was mentioned by Jim Brightly in the Hurricane road test in the December 2001 issue of Family Motor Coaching magazine (page 102). Last summer, while I was traveling from the East Coast to the West Coast and back again, my air conditioner kept failing. I had it checked on the road, but service technicians were unable to find out why. The Ford dealer could not diagnose the problem either, even with the information provided by Mr. Brightly. Do you have any more information on this subject so that I can have air conditioning in my motorhome this summer?
Willam Moeller, F270606
Wilmington, North Carolina
A: Ford’s Engineering Activity department is working on a Technical Service Bulletin (TSB) to address this issue. A technical specialist with Ford said the fix will be to go back to the 1999 F-53 dual-chamber vacuum reservoir that dedicated one chamber to the air-conditioning system. A dealer can fix the problem even without the TSB by ordering the 1999 reservoir with the vacuum harness that went with it.