Friday, June 2, 2023


Ask Dave: I can’t exercise my generator as usual. What should I do?

Dear Dave,
We store our RV inside over the winter and do not have access to it for 4 months. We are wondering what problems we might expect from our generator. Normally, we try to start it every 30–60 days and put a load on it for 15–20 minutes. But with the new inside storage we do not have that option. Your suggestions? —Bradley

Dear Bradley,
It is recommended to run the generator under load for 30 minutes once a month to lubricate the seals in diesel, gasoline, and propane generators and reduce varnishing in gasoline-powered generators. And that’s not just at idle, but rather turning on the roof air conditioner or heat pump if possible. I have talked with several diesel pusher owners that had issues with their diesel generator spilling out black smoke for several minutes and it just kept getting worse. They would run the generator going down the road several miles from the spot they were heading and it did not help. That is because they were running it in idle, not under load.

My folks had an issue with their gasoline generator when they headed to Alaska with the WIT caravan. The generator would not stay running. The Onan rep stated it was because it was not “exercised” and had varnished. Luckily, we found an “old timer” that the dealership sent us to that cleaned the carb and they were good for the rest of the trip.

I know several owners that are doing what you had been doing, going to the storage facility and running the generator for at least 30 minutes. They have not had any issues. However, you bring up a good discussion point as to what to do when this is not possible.

Winterizing your Onan generator

During an Onan Technical Certification training program that I took, they recommended changing the oil and having full fuel in the fuel tank when winterizing. They also recommended disconnecting the fuel line at the fuel filter and running the genset until it runs out of fuel. Then add Onan fuel stabilizer to the line and run it until the genset runs and get some into the fuel system. Then remove the line and run it out of fuel. It should then be OK to leave it for several months without issue. I know several people that put either STA-BIL or Sea Foam in the fuel tank and have not had a problem.

Onan also recommends to remove the spark plug and spray Onan’s Onagard Storage Fogging Spray to reduce rust and condensation in the cylinder.

Check your owner’s manual for any specifics. Let’s see what our readers are finding with their rigs.

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.

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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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Thomas D
1 year ago

MY motorhome uses the same tank for the generator. I dose the tank with seafoam about a can and a half. 1oz per gal.,then i run the onan under load ( i use a 1500 watt heater. 1/2 hour or so. Then forget it. Never do anything again until next fall when I put it away again. And I buy only no ethanol gas. The seafoam works for the coach engine too.
And if youve fail and need a new carburetor you can buy one from Amazon 1/2 price or less than from onan Cummings.

1 year ago

Sea Foam all the time when filling up the take. Turn off valve, run dry and make sure tank is full. Spring pull plug, replace turn in valve and start running 15 minutes under no load then 30 minutes under load. Ready for the season. do this with all my gens.

1 year ago

How do I say “Fake information” Run your generator one a month for 30 minutes! On our first motor home that had a generator, I was told by Onan & Winnebago to run it for 1 hour monthly under about 50% load & that was a gas gen. We now have a Diesel motor home with a Diesel generator & Onan says run the generator one a month for TWO hours…PIA, but its way too expensive to have work performed on your generators. Maybe I’m all wrong but will keep on running gen. for TWO hours once a month!

Charlie Sullivan
1 year ago

We also have a diesel generator in our motorhome, and run it 2 hours, under load, every month. This is the recommendation in the service manual and what we were told upon picking up our motorhome. We have had no problems in the 9 years we’ve owned this rig.

1 year ago

Really, disconnect the fuel line in my propane generator & run it dry? What will that do?
what are you supposed to do with propane generators? Manual does not address propane.

1 year ago
Reply to  Harry

You should still exercise it once per month under load. That will drive off moisture on the generating side and keep the slip rings in good shape. Obviously, a propane fueled generator doesn’t suffer from fuel varnishing problems like a gasoline model.

Thomas D
1 year ago
Reply to  Harry

Run the genny,turn off the gas. You do have a shut off for the genny,right. It’ll stop. You’re done. It’s the gasoline that varnish up the work’s.

1 year ago

After having to replace the carb on my gasoline 5500, I installed a toggle switch on the fuel pump power. Now when I shut the engine down I turn off main breakers and the fuel pump power. Generator runs under no load until it runs out of gas and dies. Turn the switches back on and I’m ready for the generator when needed. No problems with carb since.

Bob p
1 year ago

As far as the gas, find a station that sells non-ethanol gas to fill your tank, then run it to get the gas through the carburetor. The ethanol is what makes the gas go bad inside of 6 weeks, I’ve done that with a motorcycle that sat all winter and started up in the spring. Gas will go bad after a couple of years but nobody is going to wait that long before using their generator.

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