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RV Doctor ColumnRV Doctor #283 Dear Gary, I have a 6,500-watt Onan generator in my older Winnebago that is filling the oil crankcase with gasoline when it is run. The strange thing is that it still runs fine. The crankcase gets so pressurized that it will spray out the oil fill hole if you attempt to check the oil level before it is cooled off completely. Even then when you do remove the oil fill plug, it is so full of oil and gas, it runs out. I have already replaced the stock Onan low-pressure fuel pump. Any suggestions would help. Philip McCrary, (Atlanta, GA) Philip, your symptom is typically caused by fuel flowing past the rings of the pistons during the cranking of the generator or by a misfiring of the spark plugs. The spark plugs are the first thing to check. Be sure they are clean, dry and gapped correctly. Also, I do recall some older 6.5 KW generators back in the 80's with an internal oil flow problem in the crankcase. As designed, the crankcase has extruded baffles built into the casting of the engine block. The service bulletin listed information about drilling holes in the baffles for freer oil disbursement. I do not recommend you performing these procedures yourself as it involves total removal and disassembly of the gen-set. In fact, I would only recommend you take it to an authorized Onan service facility. Most RV technicians would not even be aware of this problem unless they have had specific Onan training. Be sure you are using the proper type of oil in the crankcase and that your breather assembly and check valve is clean and free of dirt and grime. There could be more information available about your problem but I would need the complete model number and spec number on the data plate. Feel free to resubmit your question along with the above numbers and I will dig deeper for you. Dear RV Doctor, the Duo-Therm furnace in our 1983 Southwind seems to have a mind of its own. It is a model 65930. It has had very little use, as we are mostly summer campers. This is what it does, and/or doesn't do: The burner ignites and the blower motor starts and everything runs for about two minutes then the burner goes out but the blower continues to run and will never shut off. It just blows cold air. If I reset the thermostat back to "OFF," and wait about one minute and reset the thermostat back to 72 degrees, the above cycle repeats with the same end result. The wiring diagram shows three switches, (limit, sail, and fan), plus a control module. I suspect that my trouble lies in one or more of these components. The question is which one, or ones? I'm not a bad shade tree mechanic, so with a little help from you, I'm sure this problem can be resolved. John Potter, (Hilton, NY) Well, John, your suspicions were correct except it's not a faulty switch that's causing your symptoms, but rather a correctly operating switch. The limit switch, a nonadjustable, bi-metal switch, is simply doing its job. The purpose of the high limit switch in any forced air furnace is to completely shut down the gas control valve and the voltage to the ignition module when the interior case temperature rises above its pre-set limit, hence, its name. A furnace in need of a cleaning generally causes overly high case temperatures. Considering the age of your furnace and the fact you seldom use the coach in the winter, I'd wager it's time for what's commonly called a "clean and service." Before digging out your wrenches, however, first check to make sure the heat distribution ducts are all fully open and that nothing is blocking the return air vents or the exhaust vent on the exterior of the Southwind. All of which can contribute to higher than normal temps. The reason the blower continues to run is because the fan receives its voltage, not through the limit switch, but rather through the thermostat. To stop the fan motor you must reset the thermostat. Prior to cleaning and servicing any LP furnace it is extremely important to first order and have on-hand a replacement gasket kit for your particular model. Furnace gaskets cannot be re-used because of the dangers of carbon monoxide poisoning. Gasket kits are readily available at most well-stocked RV service facilities. Your furnace will have to be removed from the motorhome, disassembled, cleaned, reassembled, and then tested before reinstalling in the coach. And as a constant reminder, all LP appliances require periodic or seasonal maintenance and all must undergo cleaning and servicing. Performed annually, as preventive maintenance, it will virtually eliminate unnecessary downtime. Obviously if you do not feel comfortable performing such maintenance tasks, by all means call your local service facility for an appointment. Dear RV Doctor, I just replaced the Winegard antenna head on our motorhome, a Pace Arrow. Now I must replace the raise and lower gear and also the rotation gear. How does one go about replacing these gears? The 12-volt booster is okay. It is located in the rear of the coach in the bedroom closet. There is a cable from the antenna to the booster and another cable that goes from it, according to some information I have, to another outlet, but I can't find where this other cable going from the signal booster goes to. I've looked everywhere. Also, there is no outside cable connection on this coach. Neil Mason, (Whittier, CA) Neil, the replacement gears should come with a set of detailed instructions. One key item to remember is to use plenty of white lithium grease when replacing the gear assemblies. If, for some reason the replacement instructions are not packaged with the gears, send me a self-addressed and stamped envelope and I'll drop a copy in the mail for you. As far as the location of that second coax outlet, check under the center of the dash, just above the engine cover. It was assumed many RVers would simply set the television on the motor housing for easy viewing from the forward living area. I believe Pace Arrow considered that and mounted the jack and adapter horizontally under the dash. That's probably also why you find so many TVs located up front in the center overhead cabinet today. Dear RV Doc, we have a Duo-Therm heat pump/air-conditioner and a Suburban gas furnace. The thermostat for the Duo-Therm heat pump works fine except the switch (between gas-electric heat and air conditioning) is stiff and you never know whether you really have it in the right position. We would like an electronic thermostat because its switch seems to work easier. (We saw one in another coach.) Unfortunately, we cannot find such a thermostat anywhere. Any ideas where we can get one? Lydia Carr, (Bakersfield, CA) Lydia, there are many aftermarket thermostats available. They are commonly found at major heating and air conditioning supply houses located all across the country. Typically though, RV service centers will only carry RV-type replacement thermostats. It is critical that any replacement thermostat match the requirements of the Duo-Therm unit. Compatibility is a mandate. The control voltage range and voltage type, (AC or DC) is extremely crucial. Digital electronic thermostats come in a variety of control modes. It is recommended that should you decide to opt for an aftermarket thermostat, first verify with Duo-Therm that an alternate thermostat will be compatible with their system. Serious and costly damage to other components can be the result of incorrect thermostat replacement. Better to be safe than sorry.
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