Onan RV Generator Maintenance — DIY or Take It To The Pros? Plus Onan Specials!

RV generators are a common topic of discussion among RVers because of the dependable power they deliver at the touch of a button, or the pull of a cord. But a generator is a complex machine that requires routine care and exercise. That’s why we take our Onan RV generator maintenance pretty seriously.

Our RV is almost 16 years old, and our Onan generator is the original unit that came with our rig. It’s never failed us, probably because it’s a high-quality brand, and we give it the respect and attention it deserves. Whether you refer to it as a generator, a genset, or a genny, it’s a great piece of gear.

Even though we often talk about the use of solar panels reducing the need for running a generator, we still wouldn’t travel without one. After all, clouds, trees, and nighttime can all hamper solar power (especially that last one). But as long as you have fuel, and take good care of it, RV generator power is super reliable.

If you want your generator to start right up and charge your batteries, or power your air conditioner or microwave, at a moment’s notice for many years to come, you’ve come to the right place. In the sections below, we’ll provide you with step-by-step video tutorials for each of the regular maintenance tasks needed by an RV generator. You’ll be able to determine whether you’d like to tackle any parts of the regular maintenance of your Onan RV generator in DIY fashion, or whether you’d prefer to let the pros keep your generator running like new.

For a summary and overview of the topic, watch the video above!

One quick note: the service intervals and procedures we reference below are for our era of Onan 7.5kW QuietDiesel generator. Be sure to check your generator’s owner’s manual for the recommended service intervals and specifics for your generator, as they may differ.

Leave RV Generator Maintenance To The Pros?

DIY videos and text serve two purposes. Obviously, they provide step-by-step tutorials for how to do a certain task. But they also can help you decide if you even want to take on that task in the first place.

Maybe you don’t have the necessary tools, and would rather not buy them. Maybe you don’t have a suitable location to do the work. Maybe you’re just not confident that you can safely and successfully complete the job. Or maybe you just don’t want to be bothered.

Regardless of YOUR reason, there are definitely times when it’s best to let the professionals handle a repair or maintenance task, instead of tackling it yourself.

Exercise Is Good For You, AND Your RV Generator

Before we dive into routine maintenance, there’s one important aspect of owning an RV generator that warrants some discussion: Exercise. We’ve heard from many RV technicians that the most problematic generators are the ones with the fewest hours on them.

Loading up on solar panels to reduce the need for running the genny is all well and good. We did that ourselves. But reducing does not mean eliminating. Like all engines, generators work best when they’re used periodically. It helps prevent “lot rot” that comes from disuse.

Best practices call for exercising (running) your generator at least once per month, under load. That means not just firing it up, but turning on enough high-draw items to ramp up the power. With our Onan 7.5kW QuietDiesel unit, we typically start the generator, let it warm up for a few minutes, and then begin to add loads. The battery charger, the electric side of the water heater, and an air conditioner or heat pump.

Don’t just start the genny and let it idle. It needs a substantial load put on it. And don’t just run it for a few minutes. The best thing you can do for your generator is to run it under high load for at least an hour or two, once a month. And then shut the loads off, and let the genny cool down for a few minutes before shutting it off.

Of course, if you run it regularly for routine use (maybe you haven’t gotten that bank of solar panels installed yet!), you won’t need to exercise it, since it’s getting all the use it needs anyway.

Oil, Air, and Spark Arrestor Care For Your Onan Generator

The first area of business on our generator maintenance schedule involves the oil and oil filter, the air filter, and the spark arrestor. We do them all at the same time because the recommended service interval is the same for all three jobs. For these tasks, you’ll need an oil drain pan, replacement oil, a new oil filter, a socket wrench, a new air filter, some nitrile gloves, a rag, a ⅜-inch socket, an 11/16-inch socket, and a socket wrench with a very long extension on it. You’ll also want something to lie on while you’re working under the RV.

Changing the Oil and Oil Filter

Service Interval: every year or every 150 hours of run time, whichever comes first.

Changing the oil in an engine, including an RV generator, is probably one of the most common DIY tasks that owners tackle. With the right tools and the ability to access the underside of your generator, it’s a fairly easy job. In our case, our generator is on a slide-out which makes access much easier than those that are fixed in place. But even if your generator isn’t on a slide, access for this task is usually pretty easy.

Cleaning the Spark Arrestor

Service Interval: every year or every 150 hours of run time, whichever comes first.

We perform this task at the same time we change the engine oil & filter. The spark arrestor traps carbon particles from the exhaust system, preventing them from being blown out of the exhaust pipe (and potentially igniting dry grass, etc). You’ll understand why this task is an important piece of Onan RV generator maintenance when you see a fair amount of soot emerging from the arrestor. Without proper maintenance, the soot is likely to plug your exhaust, causing your generator to run poorly.

If left untouched long enough, the soot can completely plug the exhaust, causing your generator to run rough or shut-down. You may then find yourself with a spark arrestor that’s rusted in place and can’t be removed. To avoid this, and poor generator performance, we clean our spark arrestor on the recommended schedule.

Replacing the Air Filter

Service Interval: every 500 hours or every year (more often if operated in dusty environments).

Other than the replacement air filter itself, you don’t need any tools for this task. It’s one of the easiest scheduled maintenance projects on our RV. A couple of wing nuts are all that hold the cover and air filter in place, so it’s easy to make quick work of the replacement.

If you’d like to watch as we complete these three annual Onan RV generator maintenance tasks to see if you’d like to tackle some (or all) of them on your generator, follow along with the video below. Again, be sure to check the owner’s manual for your generator for any additional steps that may be necessary.

Changing the Fuel Filter

Service Interval: every 500 hours, or every two years, whichever comes first.

Depending on what make and model generator your RV is equipped with, and where it’s located, your fuel filter may be more difficult to access. Check your owner’s manual for more details, and to determine if you’re comfortable tackling this procedure. You’ll also want the manual in order to confirm the exact part number for the fuel filter your generator requires.

On our Onan 7.5kW QuietDiesel generator, the fuel filter is a snap to reach. That should be true even if your genset isn’t on a slide-out, because it’s accessed from underneath.

For this task, you’ll once again need to be able to lie under the RV, so you’ll want to have a mat of some kind available. You’ll also need the following tools: an oil drain pan, a set of open-end wrenches, a socket wrench, an expendable rag, a pair of nitrile gloves, and the replacement fuel filter.

You should be aware that a small amount of fuel is going to drain from the fuel lines as you take on the task of removing the fuel filter. You’ll have the oil drain pan ready to catch most of the draining fuel, but as you turn your wrench to loosen the nuts, and as you remove the fuel filter itself, some fuel is likely to run onto your hands. You’ll want to position your hands carefully so the fuel doesn’t run down to your elbow, so be prepared for this ahead of time.

To follow along with this bit of Onan RV generator maintenance, check out this step-by-step tutorial video:

Flushing and Changing the Coolant

Service Interval: every 1,000 hours or every two years, whichever comes first.

This is the most time-consuming and involved generator maintenance task we undertake, so we’re pretty glad not to have to do it more often. Every two years is enough! (Note… we’ve since switched to using OAT long-life coolant, and therefore doubled our maintenance interval to four years. Yay!)

If your RV is not in a location where you have ready access to fresh water, or if the necessary tools and a considerable amount of time aren’t available to you, you may want to consider leaving this one to the pros.

For those of you who’d like to know more about this Onan RV generator maintenance task, here’s what you’ll need: a mat for working under the RV, some good quality antifreeze with rust and corrosion inhibitor but with NO stop-leak additives, (in this older video we used 50/50 antifreeze that gets mixed with water, but we’d recommend using OAT long-life pre-mixed, which is what we do now), some distilled or de-ionized water (if you’re not using pre-mixed antifreeze), some radiator flush, a new radiator pressure cap, a 10mm socket wrench, a clean funnel, rubber gloves, a spare rag, a pan to catch the used antifreeze, and some fresh water. You may also need a short length of plastic tubing to siphon coolant from the overflow tank.

There will be a significant amount of coolant draining into your pan in this process, so be prepared for this ahead of time, and if any coolant splashes onto your skin, be sure to wash it off immediately.

NOTE: You’ll need to run the generator several times during this process. Be sure to only handle the coolant when the engine is cold. Hot coolant is dangerous.

If you’d like to follow along as we undertake this task, including the replacement of the thermostat (which requires replacement every five years), check out this step-by-step video tutorial:

Conclusion About Onan RV Generator Maintenance

Of course, not everyone is in a position (or inclined) to go DIY on the regular maintenance for their Onan RV generator. These tasks require tools, the ability to crawl under the RV to access various parts of the generator, a location that’s conducive to working on the RV, and the time and inclination to do it all. You may decide to leave any or all of these maintenance tasks to the pros.

Even though we’re experienced DIY’ers, there are still tasks that we won’t even attempt to undertake. Both of our motorhomes were powered by Cummins diesel engines and we always left our engine, chassis, and drive train inspection, maintenance, and repairs to the pros, as we’ve explained in previous videos. We’ve had service and inspections performed by Cummins Coach Care more than any other shop, and our experience with them has been excellent over many years.

But, regardless of whether you perform your own maintenance on your RV, or take it to the professionals, you still need to keep track of what needs to be done and when. The easiest we we can recommend is to try using the RV Life Maintenance Tracker, a part of the RV Life PRO suite of tools (which we ALSO recommend).

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