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:

  • 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)
  • 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.

    Related Videos:

    Generator for RV: Understanding the Basics
    Simple Generator Precautions When Storing Your RV
    Do-It-Yourself RV Generator Maintenance
    Basic RV Generator Maintenance: What to Review Annually

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    40 Responses to “How to Winterize an RV Generator”
    1. John

      My gas power RV has been stored for 3 years in Florida before storage fresh engine and generator oil with oil stabilizer was used, I did not want to maintain storage with a full fuel tank very little fuel is in the tank and it also is stabilized with batteries disconnected. I was told that I need to start the engine every 3 months and let it run and was told something else by another source to not start it. I have not started it for 3 years what would you recommend and why. My phone is 586-994-6006 Thanks for any advise on this.

      • Customer Service Techs

        Thanks for visiting the RV Repair Club site. There are several issues you need to address with your unit now that it has been sitting for 3 years. First, you need to drain the gas tank and change the fuel filter as gas units should be stored with full fuel to reduce condensation. Your tank probably is full of water and rust which will clog your fuel filter and cause damage to your engine. Second, your engine and house batteries are more than likely dead beyond recharge after 3 years due to sulfation so you probably need new batteries. Not knowing the make, model, and year of your rig I don’t know if they are 12 v or 6 v hooked in series. Either way, you’ll need to get them checked. One thing you will find after charging or changing your engine battery is the CPU or computer that stores the setting for fuel/oxygen mix and shift points has gone back to the factory default and you will need to go through the procedure outlined in the chassis owner’s manual. Third, check the tires for pressure and weather checking on the sidewall.

    2. Rick

      I missed my monthly running of the generator (Onan 4000 gas) and when I went to start it the following month, I could not get it started. Any input as to get this gen going without having to take it to the shop?

      • jean.wozniak

        Hi Rick. Thanks for visiting the RV Repair Club site and the opportunity to assist with your generator issue. Missing one month of running the generator typically does not cause the varnishing problem we see with units stored for long periods of time, however I can’t rule that out. Since this is March and I don’t know what part of the country you are in, or the temp, here are some things to check.
        +1…Make sure the fuel tank is at least 3/4 full!
        +2…Does the unit turn over, if not, it’s not a generator problem it’s an electrical problem, check the breaker and the battery power
        +3…If the generator turns over (tries to start) does it pop and sputter like it’s almost starting, check the winter/summer or ALT setting on the Carb
        There are several troubleshooting videos on an Onan generator very similar to yours on the site.

    3. Pat

      My gas powered generator Generac Primepact 50 was started this year while I ran in and out dropping off my friend and her gear at her house. I started the generator because of the heat and i started the air conditioner. it ran for between 5-10 mins and when i came outside on the last trip to the house it had stopped. At that time i tried to restart but only the primer button worked, not the starter button. I have been home with it now 2 weeks and not even the primer works now. I thought maybe the engine ran tight, i checked the dipstick and the oil is to the top. I have not had an oil change in 5 years but i run it every year while its out to keep the gas new in the lines at the time i have to store it. A friend of mine came over and put a wrench on the starter contactor and sparks flew but he said that should have started the generator. Did i wreck my generator by not having an oil change yearly? How can i get this fixed? I don’t want to take it to a shop to get fixed.

      • Customer Service

        Hi, Pat. Thanks for visiting the RV Repair Club site. The first thing I would suggest is to remove the starter and bench test it to make sure it is turning. Although not changing oil for 5 years is never a good thing and could have caused the engine to seize, it seems odd it would start with the primer button for a period of time. This sounds more like a varnished carb and the starter needing more DC power to turn than the batteries can provide? You might try getting a battery booster and see if that at least helps get it to turn over. Sparks flying would not typically turn over a generator either.

        If you know the batteries are good, and a jump doesn’t help turn the engine over, and you bench test the starter and it works…changes are the motor is locked up.

      • Customer Service

        Hi, Lyle. Thanks for visiting the RV Repair Club site and the request for info on replacing the fuel pump on your generator. Currently the videos we have on generators goes into basic maintenance and troubleshooting but not into replacing the fuel pump. According to the manuals I could find on line, your pump is connected directly to the filter and is either located behind the control module or underneath depending on the model year. Disconnect all power coming into the genset, pinch off the fuel lines in and out, and remove the lines. If you can provide the model year, I can get a copy of the correct Service Manual which should be publication 983-0501 from Onan.

    4. Albert

      RV Make: Fleerwood, RV Model: American Eagle, RV Year: 1997, Brand: Onan, Model Number: 7500

      When I turn my generator on it will not power any of my appliances or air conditioners. How do I correct this problem. Thank you for any advice.

      • Customer Service

        Hi, Albert. We would be happy to assist you; we just need some more information. What is the make/model/year of your RV?

      • Customer Service

        Hi Albert. Thanks for visiting the RV Repair Club site and the opportunity to assist with your generator issue. The first thing you need to check are the fuses on the generator. I’m not sure what make, model or year, but a typical onboard generator has two fuses, a 30 amp that protects the line going to the distribution center and a 20 amp that goes to the back AC unit. If those are ok, check your shoreline cord to make sure you have it plugged into the J box if you don’t have an Automatic Transfer Switch (ATS). If you do have a switch, it may not be closing and allowing power thru? Check your breakers at the distribution center as well.

    5. Kenneth

      RV Make: Redwood , RV Model: 38GK, RV Year: 2015

      Are there specific recommendations for preparing a LP Generator for storage?

      • Customer Service

        Hi Kenneth. Thanks for visiting the RV Repair Club site and the opportunity to assist with your generator winterizing. With LP, you don’t have the issue with fuel varnish like gas so there is little fuel prep for winterizing. Onan recommends you change oil and filter and replace the oil with the recommended weight for the temps in your area. I would also suggest shutting off the LP line at the generator as well as the tank or cylinder, and disconnect the 12-Volt cable just to make sure there is no drain on the batteries. Some owners like to take out the spark plug and add a little fogging oil which helps with condensation and rust. Make sure you get the Onan brand just to be safe.

    6. Bricia walker

      RV Make: Wannabego, RV Model: Itasca, RV Year: 2001

      Places to going to winterazing the R V

    7. Terrance

      RV Make: Beaver, RV Model: Yorktown, RV Year: 2003, Model Number: Onan 10,000k

      glow plug maintenance, Takes 6 or more tries to start. When to replace Glow Plugs or computer chip?
      ISUZU 3LD1 motor

      • Customer Service

        Hi, Terrance. Not really sure what type of RV your Isuzu 3LD1 is in, however I assume it must be a smaller tow vehicle? The first thing you need to check is 12v going to the glow plug and then the resistance at the plug. Most of the time it’s not the computer, rather the plug. You should be able to get the Ohm resistance from your local Isuzu dealer.

    8. Patrick

      RV Make: winnebago, RV Model: Elandan, RV Year: 1991, Brand: ONAN , Model Number: 7000 WATT MARQUIS GENERATOR

      I currently have an Emerald 6.5 K watt generator. Could I replace it with the 7000 watt marquis without making any or few electrical accommodations and if so, what? Thanks in advance for your prompt reply.

      • Customer Service

        Hello Patrick,

        It doesn’t look like the electrical configurations would be an issue, rather the physical dimensions and what type of compartment you have? The Marquis is is not much larger but does have different mounting points and air flow requirements. To provide more specific information we need the make, model and year of your RV.

        David RVRC Video Membership

    9. Kent

      RV Model: Fleetwood, RV Year: 1983, Brand: chevy, Model Number: P-30

      I read this — because it related to CARBURETOR. My RV gas motor sat too long without being started due to leg injury. Now it won’t start. I have new battery so starter turns over. I added new fuel and put in quality fuel preservative and stabilizer — but maybe too little too late. Is there anything else I can do with the fuel — before calling a mechanic, which I am not? I am looking for a mechanic in the Mebane-Hillsborough area of NC along I-40/85 west of Durham, NC.

    10. Abner

      RV Make: Thor, RV Model: Vegas, RV Year: 2015, Brand: Onan, Model Number: 4000

      The generator runs but it’s not producing power to any appliances inside the coach. What’s wrong?

      • Customer Service

        Hello Abner,

        To provide more specific troubleshooting information we need the make, model, and year of your rig as well as the generator model. However, Onan is the most often used generator so here are some things to look for. First, do you have power to the appliances then plugged into shoreline through the distribution center? I’ll assume you do since it was not referenced. Next, check the two circuit breakers on the generator. For a typical 5K generator there is one 30 amp breaker for the power to the distribution center and a second 20 amp to the back air conditioner. A photo is attached for reference.

        If those are both on, check your power cord. When you plug into shoreline power, the 120-volt power comes into the distribution center and goes through circuit breakers to the appliances. When you disconnect from the shoreline power and run your generator, on some models you need to plug the power cord into what’s called a “J” box that is connected to the generator. Some models have an automatic transfer switch (ATS) that senses the power supply and switches automatically.

        David RVRC Video Membership

    11. De

      RV Make: Winnebago , RV Model: Minnie Winnie 27Q, RV Year: 2016

      We are RV newbies in our late 60’s. Hopefully, these are completely dumb questions, but the more I read, the more I realize I don’t know.
      We live in Alaska, and plan to store our RV on gravel behind my husband’s shop building (sheltered but uncovered).
      We were told by the dealer that all we needed to do for winter (we have already had it “winterized” by the dealer this past week) was turn the propane off and either disconnect or pull the coach batteries.
      From what I’ve read here, it sounds like there may be a LOT more involved! Winter will be setting in soon. The RV will not likely be moving until at least March or April once we park it.
      What are the essentials we need to check or do before parking it, and DURING the winter (sounds like shoveling a path to it mid-winter will be added to my list). Help!

      • Customer Service

        Hello De,

        Welcome to the wonderful world of RVing and hope you enjoy the rig in
        beautiful Alaska! First, if you are going to store the unit without
        access to shoreline power, it’s best to pull the batteries and take them
        somewhere inside a garage to condition them. If your rig has a
        battery disconnect and a converter that charges the batteries typically,
        yes you can start the generator if it starts on the engine battery and
        make sure the disconnect is off or disconnected. If you have an
        inverter, you probably can not start the generator without batteries?

        Second, if all the water has been removed and the unit winterized, and you
        have taken the batteries out to condition, there are a few other things
        you can do to make sure it is ready to go in the spring such as verify
        proper tire pressure, check all windows and roof vents, and fill the fuel
        tank with fuel. Check out the blog about putting the rig down for
        winter here:

        David RVRC Video Membership

    12. BOBBY

      RV Make: Winnebago, RV Model: Adventurer, RV Year: 2002, Brand: Onan, Model Number: 5500 generator

      How to remove unit.

    13. Gary Schubring

      RV Make: Winnebago, RV Model: 33C, RV Year: 2018, Brand: Cummins/Onan, Model Number: 5500

      Instead of trying to start our generator every 30 days and waste fuel, generate hours on the unit as well as the oil, why can’t we just unscrew the little drain valve on the bottom of the carb when we are done using it and just waste that? I assume because it has a fuel pump, it will not refill unless primed?

      Thanks in advance,


      • Customer Service

        According to Onan, the leader in RV generators, the only way to truly winterize the generator and get all fuel out of the carburetor is to disconnect the fuel line, run the generator out of fuel. Place the fuel line in a bucket of fuel treated with their proprietary additive, run the generator drawing this mixture for 5 minutes, then run it out of fuel again! I don’t know of anyone that would actually do that so they recommend running it under load for 30 minutes to ensure the fuel does not varnish inside the carburetor. Just draining the fuel out of the carburetor will still cause varnish to form and eventually will not start at all.

      • Customer Service

        Hi George. LP generators do not have the varnishing issue that gas or some diesel generators do so you do not need to worry about putting a fuel stabilizer or anything else in. They do recommend changing the oil as you get it ready for storage and should always exercise the generator by running it for at least 1/2 hour with a 50% load every month. I know several owners that run the generator for about and hour on close to 100% load just before storing it, then again after 2 months and have had no problems starting and running in the spring.

    14. Jim

      RV Make: Newmar, RV Model: Dutch star, RV Year: 2003, Brand: Generac, Model Number: 7500

      Generator shuts down approximately 10 minutes after starting

      • Customer Service

        Hello Jim,

        To provide more specific troubleshooting information we need the make, model, and year of the generator as well as the unit it is in. If it’s a permanently mounted model on a motorized it’s more than likely an Onan. When it shuts down, will it restart after cooling off for a period of time? Do you notice if anything puts an additional load on it such as the generator runs fine until the AC unit kicks in? Also, have you checked your winter/summer switch or altitude adjustment? I would also start by replacing the air cleaner, change the oil, and new spark plug. Start with everything clean and fresh. Next, put some fuel additive in the tank such as Onan brand or SeaFoam. If it still does it, you will probably need to take the carburetor apart and clean it really good. There is a big problem with gasoline generators getting varnish build up and having this issue and finally not starting. Onan recommends you run your generator for 30 minutes under at least 1/2 load once a month to burn out the varnish.


        RV Repair Club Video Membership

    15. fred williams

      RV Make: tiffin, RV Model: open road, RV Year: 2015, Brand: onon, Model Number: 7000

      can I turn gas supply of to generator for storage and how is this done

      • Customer Service

        Hi Fred. There should be a small shut off valve at the fuel line as it goes to the generator fuel pump. Turn the valve off and run the generator out of fuel.

    16. Ed Terlau

      RV Make: Minnie Winnie, RV Model: 27Q, RV Year: 2015

      We have a vibration that starts at 38 MPH, peaks at 44 MPH, and then gets less as the speed increases. It is still there above 55 MPH, but not too bad. I have had the wheels balanced and the three piece drive shaft rebalanced as one unit and the only change is the vibration is a little less above 55 MPH. The drive shaft shop thinks it maybe angles at the u joints. These have been checked and are within tolerances. Just for the heck of it, I tried a couple of 1/4 inch shims a each carrier bearing (one at a time) and there was very little difference. All u joints and slip joint are tight. Any suggestions? It has 10,000 miles and had the vibration from the beginning. Ford and Winnebago have not been helpful.

      • Customer Service

        Hello Ed,

        Most of the time when it is a speed related vibration, there is bad bearings or races in the wheels. I have heard of some off brand tires that cause this as well. Even if they get re balanced, the tread could be uneven when pressure is put on them and are warmed up from travel causing vibration. It is possible there is something else out of adjustment but a shop would have to measure multiple points. I would check all bushings and joints as well and make sure no seals are cracked or leaking. If you have had this problem from the beginning, it could be a manufacture error but I have seen more often that the tires or bearings are the main cause of this issue.


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    17. Pam

      RV Make: Leisure travel van, RV Model: Unity, RV Year: 2016, Brand: Cumins , Model Number: LP

      3500. It won’t start in cold. Only cranks.

      • Customer Service

        Hello Pam,

        There could be multiple things that could cause this, it also depends on if you have gas or diesel. If diesel, the fuel could be gelled if the block heater was not plugged in. There are additives that can be added to the fuel to help prevent this. On gas there could be water in the lines that could have frozen as well, they also make an additive for this as well. It could be the battery is too weak and lost the original cold cranking amps. Could be the starter failing, they have to work harder in the cold. Blocked air or fuel filters. You also want to make sure the oil you are using is rated for cold weather, check the manual and it will tell you what kind is recommended for cold weather operation.

        I hope this helps!

        RV Repair Club Video Membership

    18. fframesalma

      RV Make: Winnebago, RV Model: Brave, RV Year: 2000, Brand: Onan

      Our microwave is not fully functioning when we are under generator power. The microwave works fine when we are plugged into the power at the house. What should we do to troubleshoot the generator? 949-726-2343 Thanks, Franci

      • Customer Service


        It may not necessarily be the generator. A lot of electronics and appliances have trouble running off the generator because they typically do not put out a “true” sign wave. This can cause a lot of things to act up and not work properly. Also need to know what your generator is rated for. A lot of microwaves pull around 1600 watts, even if listed as lower they can pull more. If you are running a lot of other things, there may not be enough power to run the microwave at the same time. If the generator has too much of a load, the breakers will trip. If so, make sure you are not running too many things. The generator could need tuned up if not supplying the correct amount. Check and change the oil if needed. Check all connections and make sure the governor is set to the proper setting. The carburetor may need cleaned or a problem with airflow, such as the filter or a blockage in the spark arrestor. After doing so, you would want to check the output voltage and it should be around 115v-120v. If the breakers are fine, the generator has not been overloaded and the problem may be elsewhere. There could be other problems, like a wiring issue at the transfer switch not allowing sufficient voltage to the unit. Make sure the check all wires and connections coming from the generator. You would want to check the voltage in an outlet before and after the microwave is turned on, make sure it doesn’t drop too low.

        I hope this information helps!

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