How to Winterize an RV Generator

Whether putting your RV to bed for a long winter’s nap, or just getting it ready for an extended siesta, it’s important to know how to winterize an RV generator for an extended period of rest.

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. This is especially important for diesel RV owners. If the temperature is going to dip below freezing, Onan recommends filling the tank with a winter grade fuel as listed in their owner’s manual.

Diesel Generators

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

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.

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.

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.

LP Generators

Although it’s a good idea to use fresh gas and a full tank for your RV, an LP generator is not affected by the fuel used for the drive train. However, Onan does have recommendations for the type of propane: 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.

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

The next step in how to winterize a RV generator is to 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 its 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 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 manufacturer’s 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 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:

Gasoline Engine Oil Quality

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.

Diesel Engine Oil Quality

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.

Oil Viscosities

Use the following chart to select correct viscosity grades for expected ambient temperature range.

NOTE: Multi-grade oils (such as SAE 15W-40) are recommended for year-round use in Cummins Onan liquid-cooled engines,or as a good all-season oil for air-cooled engines.

NOTE: SAE-30 is the preferred summer grade for optimum oil consumption control in Cummins Onan air-cooled engines.

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.

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