Frequently Asked Questions
Do you have a question about a Cummins Onan product? Browse through our Frequently Asked Questions below -- you may find that we already have an answer for you. We will be adding new questions regularly, so please check this page often.
If your question isn't addressed here, please contact your local Cummins Onan Certified Distributor/Dealer for assistance. They are your local source for Cummins Onan parts and accessories, manuals, technical advice, maintenance service and repairs. Or if you already own a Cummins Onan RV generator you can download or view your operators manual online.
Is there a break-in process for a new Cummins Onan RV generator?
Yes, your generator will perform better if you follow the break-in procedure recommended in the Operator's Manual. This typically involves running the generator at about 50 percent load for two hours, then at about 75 percent load for two hours, then letting it cool down. You should change the engine crankcase oil after the first 20 hours of operation, and every 100 to 150 hours thereafter. See your Operator's Manual for advice specific to your model.
Do diesel generators need exercising like gasoline generators?
Yes, regular exercise helps lubricate the seals and engine components and keeps carbon from building up. Regular exercise also heats up the generator windings and removes or expels excess moisture. In sets equipped with brushes, exercising helps prevent corrosion build up on the slip rings.
How often should I run my gasoline generator to keep it in good condition.
It may seem strange that not using a machine could cause performance problems, but with RV generators that's exactly the case. Regular "exercise" is an important part of keeping your generator healthy. Lack of use can cause moisture build-up and fuel system damage that makes it run poorly. In fact, in as little as 30 days, the fuel in gasoline-powered generators can begin to break down into gums and varnishes that clog the fuel system. Fuel varnishing results in hard starting and surging. (A surging generator never settles at a stable operating speed.)
To prevent such problems, we recommend running gasoline generators at a minimum of 50 percent capacity (for example, 2000 W, or one air conditioner for a 4000 W set) for two hours at least once every four weeks. A long two-hour exercise period is preferable to several short periods.
Is generator power clean enough to run a computer?
Yes, with Cummins Onan generators this is no problem. The generator set should be turned on and warmed up before turning on the computer. The normal precautions for home use should be followed for RV use as well.
What is carburetor icing? What conditions cause it? How can it be prevented?
Carburetor icing occurs in damp, cool outside conditions, causing rough operation, stalling and throttle sticking. If your generator is equipped with a summer/winter lever, operate the generator in the "winter" position in humid temperatures of 55 degrees F or less. This will pre-heat the intake air so ice won't form in the carburetor.
Can I operate an air conditioner and microwave at the same time?
Most current models of Cummins Onan generators can operate both of these appliances at the same time. Although this is possible in lower temperatures or altitudes or with high efficiency AC's, Cummins Onan 2500 and 2800 watt generators will probably be overloaded when the AC cycles off and on with the microwave running. Load shedding devices are available that automatically turn off the AC when the microwave starts and then restarts it when power is available again.
How many air conditioners can be powered by an Cummins Onan RV genset?
It depends on the model and the total power demands of other appliances you are running at the same time. But in general, smaller Cummins Onan generator sets can operate one air conditioner with power to spare. Larger models such as the Quiet Diesel Series of generators can power two or three air conditioners at a time. Visit our Generator Selector to find the generator that meets your power requirements.
Is it practical to power the roof air conditioner with my generator while traveling on the road?
Yes, that is what a generator is for -- portable electrical power. In fact, it can help you economize on your vehicle's fuel because the generator uses less fuel. Plus, it gives you an opportunity to exercise your generator. Any appliance that can be run in a stationery position can also be powered while driving.
What happens if I "short-cycle" my air conditioner?
Short cycling refers to stopping and restarting the air conditioner compressor before the refrigerant pressure has enough time to equalize. If this happens, one of several things can occur: a circuit breaker may trip, either on the generator or at the breaker panel; the generator engine may stall; the AC compressor may trip its overload. AC compressors should remain off for at least 3 minutes before being restarted.
Why does a breaker trip and the rear air conditioner not work when I turn it on while the generator is running?
RVs with two air conditioners typically have a 20-amp circuit breaker for the rear air conditioner and a 30-amp breaker for all other loads (including the front air conditioner). The RV may be wired with the two circuits reversed, causing the breaker to trip. The generator connections and wiring should be checked by an authorized service location.
Will high efficiency (power saver) air conditioners provide more reserve power?
YES. High efficiency AC's use 30% less power and are easier to start. That means more power is available for use in the RV for better fuel economy. High efficiency AC's also have higher cooling output than comparable standard AC's.
Can my generator charge my RV house battery?
Not directly. But a generator does provide power to operate your converter/charger, that charges batteries. Many diesel generators also have an alternator, that can charge batteries.
Is generator power clean enough to run a computer?
Yes, with Cummins Onan generators this is no problem. The generator set should be turned on and warmed up before turning on the computer. The normal precautions for home use should be followed for RV use as well.
Can LP fuel plug up the regulator?
The most common contaminants found in LP fuel are the oils from the LP pumping facility. The oil is removed from LP fuel at the location where the fuel vaporizes. In liquid withdrawal LP fuel systems, this occurs in the regulator. Oil contaminants can then clog the regulator. The larger QG series generators liquid withdrawal LP fuel systems provide a drain for oil removal. See your Cummins Onan Certified RV Service and Parts Dealer for assistance.
Can my Cummins Onan diesel powered generator use B5 alternative fuel?
B5: 5% bio-diesel. Our Diesels are capable on running up to B5 (5%) bio-diesel. There are no changes to performance or maintenance requirements.
Can my Cummins Onan diesel powered generator use ULSD alternative fuel?
ULSD: Ultra Low Sulfur Diesel. This fuel is now available across the country. 2007 and newer model diesel motorhomes are required to use it for the main propulsion engine. Cummins Onan generators will function properly on ULSD with no change to performance or maintenance intervals.
Can my Cummins Onan gasoline powered generator use alternative fuels?
E85: Ethanol/Gasoline mix. E85 in not approved for use in any Cummins Onan gasoline generator and will not function on this fuel.
How is LP fuel supplied to my generator?
LP fuel is stored in the fuel tank in liquid form with some vapor at the top of the tank at relatively high pressure. The pressure in the tank is determined by the ambient (outdoor) temperature. The higher the temperature, the higher the pressure. Ambient heat vaporizes fuel until the pressure won't allow any more liquid to vaporize. The tank pressure will be about 200 psi at 110 degrees F, 70 psi at 40 degrees F, and 0 psi at -40 degrees F.
In order for the fuel to be burned at a controlled rate in the generator (or any other appliance) it must be converted to a vapor form and supplied at a controlled pressure.
LP fuel systems for many Cummins Onan generators are available in two forms, vapor withdrawal and liquid withdrawal.
Should I get an LP or a diesel generator for my diesel motorhome? What are the differences?
Each fuel option has its own advantages. LP generators generally have a lower initial cost than diesel units. Plus, they're smaller and lighter weight, allowing for more flexibility in the floor plan of large RVs. LP generators also have less exhaust fume smell. Diesel generators have a much longer engine life. They consume less fuel and diesel fuel usually costs less than LP for additional savings. A diesel generator gives you a common fuel system and the convenience of operating your generator from the vehicle's main fuel supply. The generator best for you depends on how you use it and your own personal preferences.
What are the advantages of an LP Vapor versus an LP Liquid fuel system?
LP Vapor Withdrawal is a simpler system for the generator set, and uses the same low-pressure vapor system as other appliances. LP Liquid Withdrawal offers better operation in cold temperatures and a complete vaporization pressure regulation system is on the generator from the factory.
Will high-octane gasoline reduce the amount of fuel varnish?
No, because varnish is a form of fuel degradation that is not a function of octane level. Rather, it is a function of fuel quality, age and additive treatment. High-octane fuel without a stabilizer additive will oxidize or varnish at a faster rate than fuel treated with a fuel stabilizer.
Once the generator is started, should it continue to run for a certain length of time?
Ideally, Cummins Onan generators should run for a minimum of 30 minutes to give them a chance to warm up. Once warmed up, running your generator for five-minute intervals should be fine. But remember to turn on some appliances so the generator works while it's running. Running it for more than 30 minutes at no load only burns fuel unnecessarily and adds costly maintenance.
How frequently should I change oil if I won't be using the generator for several months?
Typically, just like a car, change oil for seasonal temperature changes. For long storage, see your Operator's Manual for extended out-of-service protection.
Should I use straight 30-weight oil in my RV generator set or is the multi-viscosity oil I use in my vehicle okay?
You can use any premium quality engine oil in the correct oil viscosity for your generator's typical operating temperature range. Avoid mixing different grades or brands.
The replacement oil filter (part #122-0833) that I purchased for my Cummins Onan Quiet Diesel looks like the wrong size.
We hear this a lot! Filter #122-0833 has replaced filter #185-5801 and filter #185-5409. Despite the difference in outward appearance, it will fit your set and the oil ring will provide a proper seal.
When I'm checking my oil, does the dipstick need to be screwed in all the way?
In order to get the correct oil level reading, the dipstick must be screwed in completely on all models with a screw-type dipstick, except for the 2800 and 2500 QG Series, MicroLite and Camp Power models; it sits on top of the fill tube. Make sure the vehicle is level when checking oil level.
How are "will-fit" generator replacement parts different from Onan Green Label Parts?
Onan genuine Green Label Parts are tested and designed specifically for RV applications. Will-fit parts and gaskets can be the correct shape, but because of inadequate design, the wrong material, or poor quality, they could cause premature failure, leakage or performance problems. Use of some non-Onan replacement engine parts may affect the unit's emissions certification. Damage caused by the use of oil and air filters other than Green Label Parts is not covered under your generator warranty.
Why don't I have as much power as I think I should?
Battery chargers run as "invisible" loads and can draw as much power as two air conditioners, depending on size. This can continue for several hours, depending on battery charger and battery bank size.
Will increasing the speed (accelerating the RPM) on my generator provide more power potential?
No, and it may damage your generator and appliances.
How do I keep mice/rodents out of my generator during storage?
Use rodent prevention techniques around the generator/compartment just as you would with any other area of your RV.
Can I run my generator for extra power while I'm hooked up to shore power at a campground?
Only if the RV manufacturer has supplied a separate circuit for a second air conditioner. However, in most RVs with two air conditioners, only one will operate while plugged into commercial shore power. By the NFPA code you cannot connect both power sources, generator power and commercial shore power, together. RV electrical systems are designed to separate these two power sources. However, with your comfort and needs in mind, your RV manufacturer may have wired the RV to allow you to power your second air conditioner with your RV generator. Check your vehicle's operator manual.
Can I run an RV generator in a National Park?
Yes. Cummins Onan installed generators are quieter than the National Park sound level requirements (during allowable hours of use).
My generator won't start. What should I check?
Download a copy of your operators manual for a list of troubleshooting tips or use our sales and service locator to find your nearest qualified Cummins Onan service dealer.
