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The famous line from Star Trek’s “Scotty” while in the engine room was: “Captain, we need more dilithiam crystals!”  In other words, more power and it seems like that’s the case with today’s RVers as we are all trying to get the most out of every appliance we can get our hands on!

Ok, maybe not everyone, however a generator is an important component to not only help run appliances, but also charge the house batteries when dry camping or boondocking.  For the most part, generators require a limited amount of maintenance, however there are some things you need to know to make sure they provide the power you need and run as long as you need them to.  In this article we will cover permanently mounted or onboard generators.

Types of generators and their maintenance requirements:


Typically in a motorized RV, these generators are permanently mounted with rubberized motor mounts to the frame, although some are used in Toy Haulers as the fuel for these needs to be supplied by an onboard fuel source such as the gasoline tank.

Sizes can range from smaller 2000 watt versions, that have limited power, to the large 7000 watt version shown here that has enough power to make “Scotty” happy!

Gasoline fuel generators can use regular unleaded or an Ethanol Blend not to exceed 10% Ethanol.  The key is to use fresh gas, nothing older than 30 days, which is why it’s a good idea to run the tank low before refilling prior to storage. 

Larger generators (5000 watts and higher) have two circuit breakers on the generator itself, one that supplies 30 amp power to the distribution center, and a 20 amp breaker that is connected directly to the bedroom air conditioner if applicable. This allows you to run both roof airs with the front supplied by the distribution center and the back by the direct line on the generator.

Recommended maintenance includes changing oil as well as the oil and air filters.

Whether putting your RV to bed for a long while, or just getting it ready for an extended siesta, it’s important to take a little time preparing your generator for an extended period of rest by following these steps:

Step One – Fuel Recommendations

The first step is to make sure your fuel tank is full before letting it sit for anything longer than 30 days.  A partially full fuel tank allows condensation to form inside the tank which not only adds water to the mix, but can also lead to rust forming and causing all kinds of issues.  Most seasoned RVers calculate their storage/winterizing schedule and let the fuel tank get low prior to storage so they can fill it with the proper fresh fuel before storing. 

Step Two – Stabilize The Fuel Supply

Any fuel will deteriorate as it sits in an engine or fuel tank for a period of time, usually as quick as 30 days.  Gasoline will start to varnish producing a gummy residue that clogs the carburetor, fuel filter, and fuel pump and affects performance.  Unlike engine performance or fuel economy, the octane level or grade of fuel has little effect on the time factor of this fuel deterioration.  Diesel fuel does not deteriorate and produce varnish like gasoline, however it can suffer biological growth (algae) and gel in cold weather which will also affect engine performance. 

It is recommended to use a quality fuel preservative and stabilizer with either diesel or gasoline models.  There are several brands on the market with most of the popular diesel stabilizers available at the major truck stops.  Onan recommends OnaFresh fuel preservative and stabilizer. 

Keep in mind, once a fuel starts to deteriorate and varnish is present in the generator, a preservative and stabilizer will not restore the fuel.  At this point you will need to try a fuel system cleaner or disassemble the generator components and clean/remove the contaminants. 

Step Three – Run The Unit

Run the unit under load for at least 30 minutes.  The Onan owner’s manual recommends 30 minutes plus 2 minutes for each foot of fuel line to ensure the stabilizer makes it way through all the lines and engine components.  Other Onan service documents recommend running for 1-2 hours.  Running the unit for 1 hour should be sufficient and make sure you have something on the inside that will provide a load to the generator like the roof air units or plugging in an appliance like a space heater.

Step Four – Change The Oil And Filter

After running the unit, it’s recommended to change the oil and filter prior to storage.  This prevents acids from accumulating which could corrode bearings inside the engine.  It’s important to use the manufacturers original parts for oil filters and recommended oil.  Generic or replacement parts commonly referred to as “will-fit” parts are built for cost, not quality.  These parts often times have inferior materials used for filtering, sealing, and longevity which could cause expensive failures. 

Onan has blended their own specific oil branded as OnaMax, however they do allow other brands under warranty as long as they meet the following specifications:

– Use oil meeting any of the following API performance categories: SJ, SL or SM where SM is currently the highest quality available. Look for the “Energy Conserving” designation to optimize fuel economy.

Check your owner’s manual for weight or viscosity according to your genset and temperatures.

Step Five– Gasoline Engine Fogging

If you own a gasoline fueled RV generator it’s recommended to remove the spark plug and spray Onan’s OnaGard fogging spray to reduce rust and condensation in the cylinder.

Step Six – Check Connections

Make sure all cables, wires, and other connections are tight and protected.  You may need to clean battery cable connections and lubricate linkage points.

Step Seven – Disconnect The Battery

It’s a good idea to disconnect the ground terminal to the generator to eliminate any battery drain or accidental surge back from the house system if the unit is plugged in for storage.

Onan also recommends running the generator once a month for at least 30 minutes under 50% load to reduce the gasoline deterioration and varnish and keep the seals softened in the diesel and LP units.  In some situations this is not possible, so it’s important to take the necessary steps to clean, protect, and stabilize the fuel source to make sure your generator performs well for years to come.

Liquid Propane/LP

Propane fueled generators are not as common as gas or diesel since LP is a very precious commodity when dry camping or boondocking which is when you need a generator!  Some diesel pusher owners choose the LP genset as it originally ran quieter and did not have the smell of the diesel fumes; however, for the most part this has not been a factor with the newer diesel genset models.  Some trailer owners use this model as they do not have a gas tank other than the tow vehicle which they can not tap into and want a permanently mounted unit.

Propane generators do require a similar oil and filter change maintenance schedule and Onan has the following recommendation for the proper fuel:

— Use clean, HD-5 grade liquid propane in a mixture of at least 90% propane. Propane fuels other than HD-5 can contain more than 2.5 percent butane which can result in poor fuel vaporization and poor engine starting in outside temperatures below 32°F.

Propane generators are not as subject to the varnish issue that gasoline models are, however it is a good idea to run the generator periodically to lubricate the seals and gaskets.  Onan recommends running it for 30 minutes 2-3 times yearly.

Diesel Generator

The diesel generator has come a long way since I took to the road training dealers back in the mid 1990’s. OK I admit, most things have come a long way since that time!  Back then there were only 4 Rocky films and only 3 Star Wars films!

This unit is fueled by the chassis fuel tank just like the gas version and has the same maintenance schedule as the gas and propane with just a couple of additional items to be aware of.

Ensure the fuel selected for use has a minimum Cetane number of 45. No. 2-D or No.2-DLS diesel fuel gives the best economy and performance under most operating conditions. Use No. 1 diesel fuel when ambient temperatures are below 32°F and during long periods of light engine load. Use low sulfur or ultra low sulfur content fuel having a cloud point of at least 10°F below the lowest expected fuel temperature. Cloud point is the temperature at which wax crystals begin to form in diesel fuel.

Onan does have some recommendations for fuel type:

— Use any of the following ASTM certified fuels for your quiet diesel:

  • ASTM-No.2-D (ambient temperature greater than 23°F) (No. 2 Diesel)
  • or ASTM-1-D (No. 1 Diesel)
  • No.2-DLS (ambient temperature greater than 23°F)
  • No.1-D (ambient temperature less than 23°F)
  • No.1-DLS (ambient temperature less than 23°F)
  • B5 Biodiesel(ambient temperature greater than 50°F)

B20 Biodiesel

− The use of B20 biodiesel requires the generator to have an additional fuel/water separator. Long-term storage of biodiesel fuels can result in oxidation and/or mold growth. Consult your vehicle manufacturer and your generator owner’s manual to see if this option is applicable to your generator.

– Use oil meeting any of the following API performance categories: CF, CF-4, CG-4, CH-4, CI-4 or CJ-4 where CJ-4 is currently the highest quality available. The use of synthetic oil is not recommended during the warranty period. The use of oil meeting API performance category CF-4, CG-4, CH-4 or CI-4 while burning fuel with a sulfuric content greater than 0.5% or CJ-4 while burning fuel with a sulfuric content greater than 0.0015% is not recommended as oil service is negatively impacted.

Check your generator owner’s manual for recommended weight/viscosity for temperatures.

About the author: Dave Solberg: Managing Editor, RV Repair Club

For the last 25 years, Dave has conducted RV maintenance and safety seminars, developed dealer and owner training programs, written RV safety and handyman articles, authored an RV handbook reference guide and logged over 100,000 miles on the road in an RV.

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