Keeping your Onan RV generator (Cummins/Onan) in top condition is the only way to ensure it operates when you need it most.
You never know when emergencies can arise, and you lose shore power at your residence, RV park, or campground. You may also love off-grid camping, where a generator can be necessary to keep RV appliances running.
This quick-reference guide will help teach you how to maintain your Onan RV generator and explain how and when you need to change the oil, replace the air filter, change the spark plug, and clean the spark arrestor.
So if your motorhome, travel trailer, or fifth wheel camper relies on an Onan generator to keep you camping in comfort, keep reading to learn how to master these tasks!
Keeping Your Onan Generator Healthy
Basic generator care begins by performing oil changes and other maintenance per manufacturers’ instructions for the Onan RV generator model you own.
Most generators will require an oil change at least once a year, or around every 50-150 hours you put on the unit.
Changing the air filter every 500 hours or once a year is recommended, but it may need replacement more often if you camp in a dusty region.
Replacing the spark plug needs to be done about every 450 hours to keep the generator firing correctly.
Lastly, cleaning the spark arrestor every season will help keep your Onan RV generator in top shape.
You also need to run the generator at least once a month for about an hour to keep the oil circulating and parts lubricated. Not running an RV generator for months on end, such as leaving it to sit during winter storage and then getting upset when it won’t start, is an all too common scenario that you can avoid.
Make sure when you run the generator, you turn on an RV appliance so it draws a load and operates entirely.
Onan RV Generator Maintenance
Below are the three most crucial tasks you’ll need to perform to keep your Onan RV generator operating correctly.
How to Change the Oil in an Onan RV Generator
Here are the basic steps to change the oil in your RV Onan generator. Always refer to your specific model’s owner’s manual for more details on maintaining the oil.
Tools and supplies you’ll need before you start:
- 3/8″ drive-9/16″ deep socket
- 1/4″ drive T-30 internal Torx socket
- No. 5 Pipe Thread sealant
- Oil pan and funnel
- 2 quarts of Cummins 3265336 Onan SAE 15W-40 Oil
- Onan replacement oil filter and oil-filter wrench if your generator uses one
Step 1. Run the Generator a Short Time
Before draining the oil, you’ll want to run the generator for about ten minutes to warm it up. Once it’s warm, shut the generator off.
Step 2. Remove the Panel That Covers the Oil Drain Plug
There will be a panel that covers the drain plug for the oil tank that you must remove.
In some instances, the panel is on the underside of the generator, and you’ll need a T-30 Torx bit/socket to fit the screw heads. If you remove one screw and slightly loosen the other, you can swing the panel out of the way, which is helpful to avoid losing parts and is faster to reattach when the oil change is complete.
Some other models of generators, such as the Onan 5500 RV Generator, will have the drain plug access in the lower right-hand portion of the front panel, with the drain tube underneath the unit. This drain plug will have tabs to help turn the fitting so you won’t need a special tool.
Step 3. Remove Oil Drain Plug and Drain the Tank
To remove the drain plug from the generator, use a 9/16 socket. Have your oil pan situated to catch the fluid, and let it drain completely.
Step 4. Re-Install the Drain Plug
Before you reinstall the drain plug in your Onan RV generator, add pipe thread sealant to the screw threads to ensure a leak-proof seal.
If you have a torque wrench, use it to tighten the drain plug to the manufacturer’s recommendation, so it’s not overtight.
Step 5. Fill RV Generator with Fresh Oil
To add in fresh oil, remove the oil tank cover. Then, insert the funnel into the opening and pour in the new oil.
Many Onan RV generator oil reservoirs hold 1.6 quarts, but check your manual for the exact amount. It’s best to always use synthetic oil in the generator, with Cummins 3265336 Onan SAE 15W-40 Oil highly recommended.
After filling, check the level to ensure you didn’t overfill the tank. Once you verify the correct oil level, put the oil tank cap back on.
Step 6. Run the Generator and Check for Leaks
Before you reinstall the panel that covers the oil drain plug, run the generator for a few minutes so you can check it for leakage.
If you don’t see any oil dripping from the plug, you can turn the generator off and screw the panel back into place to finish the job of changing the oil in your Onan RV generator.
Step 7. Change the Generator Oil Filter (If Necessary)
Some Cummins Onan RV generator models, especially larger units, have an oil filter you’ll want to replace at this time.
To access the filter, you’ll reach underneath the generator, just inside the edge of the recreational vehicle.
Use your oil-filter wrench to unscrew the filter from the generator. Please note that if this is the first time you’re replacing the oil filter after factory installation, it tends to be very difficult, so expect to use more force than usual.
Do yourself a favor, and invest the few dollars in a universal oil filter wrench attachment.
This tool is much easier to use on RV generators due to the oil filter’s location and depth within the unit. In addition, you can use the device on all sizes of oil filters for other vehicles and equipment.
How to Replace the Air Filter in an Onan RV Generator
Changing out the air filter in your Onan RV generator is very straightforward.
Once you remove the generator’s front panel to access the working components, you will see a vertically-placed flat black box with a plastic lid that covers the air filter.
Remove the cover by flipping open the latches on the sides and pulling it forward. Underneath, you will see the air filter for the generator sitting inside the housing.
Grasp the edges of the filter and pull it towards you to remove it from the housing.
Turn the filter over to check how dirty it is. If it shows signs of obvious dirt and discoloration, replace it with a new OEM Onan air filter for your size of RV generator.
If the air filter looks clean, you can reuse it. Before putting the new or old air filter back into the housing, clear away any bugs or loose debris you see inside.
Place the filter into the housing and reinstall the cover by first slipping the tabs on the top into the corresponding holes on the generator, then bringing it down and latching the side and bottom clips.
The whole process of changing the RV generator air filter should only take a couple of minutes to complete.
How to Change the Spark Plugs in an Onan RV Generator
To prepare to change the spark plug on your Onan recreational vehicle generator, you’ll need a 13/16″ spark plug socket and ratchet, swivel, extension, and an Onan replacement spark plug. Check your owner’s manual for the correct Onan spark plug number, as they sell a few different types.
Follow the steps below to change your Onan RV generator spark plug.
Step 1. Turn Off the Generator
Always turn off the generator and unplug your RV before you attempt to check or change out your RV generator spark plug. If the unit was running, give it time to cool down before starting this spark plug inspection or replacement.
Step 2. Remove the Main Generator Panel and Spark Plug Cover
You’ll need to remove the front access panel to reach the spark plug or plugs on your Onan generator.
Check your owner’s manual for the diagram of spark plug locations on the generator, but typically one will be found on the upper right-hand side next to a silver panel. In addition, you may find a secondary plug on the upper-left side near the back of the unit on some Onan RV generator models.
The spark plugs will have a black wire running to them and a rubber boot over the top you need to remove carefully to avoid damaging the wire.
Step 3. Remove the Spark Plug(s) From the Generator and Insert New One
Using your socket and ratchet, remove the spark plug from the generator by unscrewing it from its port.
Insert and tighten up the replacement generator spark plug.
Reattach the wire and boot, which may be challenging due to tight quarters, but getting a snug fit is crucial for optimal performance. You should hear a click when it makes the proper connection.
Step 4. Start the Generator
After you reinstall the new spark plug, power on and start the generator to ensure the connections are solid.
If the generator misfires, you’ll need to tighten the plug or the wire connector and try again until it runs smoothly.
Step 5. Replace Front Access Panel
Once your new spark plugs are in and working correctly, you can turn the generator off and replace the front access panel to complete the job.
Oil Change Annual Service Oil Spark Plug Air Filter (Video)
How to Clean the Onan RV Generator Spark Arrestor
A spark arrestor on the generator aims to prevent fires by stopping any hot particles from exiting the engine. Deposits can build on this screen and cause issues.
To clean the spark arrestor on your Onan RV generator, follow these steps:
Step 1. Allow the Generator to Cool Down
Never try to perform maintenance tasks on a hot generator. Instead, turn the unit off, and give it enough time to cool down so any metal components you need to handle aren’t hot so that you can avoid burns.
Step 2. Unscrew and Clean the Generator Spark Arrestor
Remove the screws that hold the spark arrestor screen bracket in place and pull it off the generator.
Take a small wire brush and gently scrub at the screen from both sides to remove carbon and rust buildup. If the spark arrestor screen has holes or is torn, replace the part.
Step 3. Re-Install the Spark Arrestor
After the screen is as clean as possible, replace it over the hole, insert the round bracket over the edges, and tighten up the screws.
Onan RV Generator Maintenance || Change the Oil, Replace the Air Filter, & Clean the Spark Arrestor (Video)
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Onan RV generators have a reputation for being extremely reliable and powerful, but they will only remain that way if you maintain them properly.
Taking care of the tasks above in this Onan RV generator maintenance guide, as well as any other measures set in the owner’s manual, is part of keeping your recreational vehicle in safe working order.
I do hope this guide encourages you to stay on top of this crucial DIY RV generator maintenance, so you can be sure your generator will work when you need it most!
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-- Andre Gide